DSpace Community:
http://hdl.handle.net/2381/316
2015-03-27T20:55:02Z
2015-03-27T20:55:02Z
From Communicating Machines to Graphical Choreographies
Lange, Julien
Tuosto, Emilio
Yoshida, Nobuko
http://hdl.handle.net/2381/31932
2015-03-27T15:39:14Z
2015-03-27T15:38:12Z
Title: From Communicating Machines to Graphical Choreographies
Authors: Lange, Julien; Tuosto, Emilio; Yoshida, Nobuko
Editors: Rajamani, S. K.; Walker, D.
Abstract: Graphical choreographies, or global graphs, are general multiparty session specifications featuring expressive constructs such as forking, merging, and joining for representing application-level protocols. Global graphs can be directly translated into modelling notations such as BPMN and UML. This paper presents an algorithm whereby a global graph can be constructed from asynchronous interactions represented by communicating finite-state machines (CFSMs). Our results include: a sound and complete characterisation of a subset of safe CFSMs from which global graphs can be constructed; an algorithm to translate CFSMs to global graphs; a time complexity analysis; and an implementation of our theory, as well as an experimental evaluation.
2015-03-27T15:38:12Z
Resolving non-determinism in choreographies
Bocchi, L.
Melgratti, H.
Tuosto, Emilio
http://hdl.handle.net/2381/31873
2015-03-17T02:02:13Z
2015-03-16T11:59:32Z
Title: Resolving non-determinism in choreographies
Authors: Bocchi, L.; Melgratti, H.; Tuosto, Emilio
Abstract: Resolving non-deterministic choices of choreographies is a crucial task. We introduce a novel notion of realisability for choreographies -called whole-spectrum implementation- that rules out deterministic implementations of roles that, no matter which context they are placed in, will never follow one of the branches of a non-deterministic choice. We show that, under some conditions, it is decidable whether an implementation is whole-spectrum. As a case study, we analyse the POP protocol under the lens of whole-spectrum implementation. © 2014 Springer-Verlag.
2015-03-16T11:59:32Z
Inferring Extended Finite State Machine Models from Software Executions
Walkinshaw, Neil
Taylor, R.
Derrick, J.
http://hdl.handle.net/2381/31765
2015-03-05T02:02:28Z
2015-03-04T16:59:57Z
Title: Inferring Extended Finite State Machine Models from Software Executions
Authors: Walkinshaw, Neil; Taylor, R.; Derrick, J.
Editors: Robbes, R.; Oliveto, R.; Di Penta, M.
Abstract: The ability to reverse-engineer models of software behaviour is valuable for a wide range of software maintenance, validation and verification tasks. Current reverse-engineering techniques focus either on control-specific behaviour (e.g., in the form of Finite State Machines), or data-specific behaviour (e.g., as pre / post-conditions or invariants). However, typical software behaviour is usually a product of the two; models must combine both aspects to fully represent the software's operation. Extended Finite State Machines (EFSMs) provide such a model. Although attempts have been made to infer EFSMs, these have been problematic. The models inferred by these techniques can be non-deterministic, the inference algorithms can be inflexible, and only applicable to traces with specific characteristics. This paper presents a novel EFSM inference technique that addresses the problems of inflexibility and non-determinism. It also adapts an experimental technique from the field of Machine Learning to evaluate EFSM inference techniques, and applies it to three diverse software systems.
Description: INSPEC Accession Number: 13916984
2015-03-04T16:59:57Z
Minimum Spanning Tree Verification under Uncertainty
Erlebach, Thomas R.
Hoffmann, Michael
http://hdl.handle.net/2381/31666
2015-02-14T02:01:26Z
2015-02-13T11:59:12Z
Title: Minimum Spanning Tree Verification under Uncertainty
Authors: Erlebach, Thomas R.; Hoffmann, Michael
Abstract: In the verification under uncertainty setting, an algorithm is given, for each input item, an uncertainty area that is guaranteed to contain the exact input value, as well as an assumed input value. An update of an input item reveals its exact value. If the exact value is equal to the assumed value, we say that the update verifies the assumed value. We consider verification under uncertainty for the minimum spanning tree (MST) problem for undirected weighted graphs, where each edge is associated with an uncertainty area and an assumed edge weight. The objective of an algorithm is to compute the smallest set of updates with the property that, if the updates of all edges in the set verify their assumed weights, the edge set of an MST can be computed. We give a polynomial-time optimal algorithm for the MST verification problem by relating the choices of updates to vertex covers in a bipartite auxiliary graph. Furthermore, we consider an alternative uncertainty setting where the vertices are embedded in the plane, the weight of an edge is the Euclidean distance between the endpoints of the edge, and the uncertainty is about the location of the vertices. An update of a vertex yields the exact location of that vertex. We prove that the MST verification problem in this vertex uncertainty setting is NP-hard. This shows a surprising difference in complexity between the edge and vertex uncertainty settings of the MST verification problem.
2015-02-13T11:59:12Z
Query-competitive algorithms for cheapest set problems under uncertainty
Erlebach, Thomas
Hoffmann, Michael
Kammer, F.
http://hdl.handle.net/2381/31664
2015-02-14T02:01:39Z
2015-02-13T10:03:39Z
Title: Query-competitive algorithms for cheapest set problems under uncertainty
Authors: Erlebach, Thomas; Hoffmann, Michael; Kammer, F.
Abstract: Considering the model of computing under uncertainty where element weights are uncertain but can be obtained at a cost by query operations, we study the problem of identifying a cheapest (minimum-weight) set among a given collection of feasible sets using a minimum number of queries of element weights. For the general case we present an algorithm that makes at most d·OPT+d queries, where d is the maximum cardinality of any given set and OPT is the optimal number of queries needed to identify a cheapest set. For the minimum multi-cut problem in trees with d terminal pairs, we give an algorithm that makes at most d·OPT+1 queries. For the problem of computing a minimum-weight base of a given matroid, we give an algorithm that makes at most 2·OPT queries, generalizing a known result for the minimum spanning tree problem. For each of our algorithms we give matching lower bounds.
2015-02-13T10:03:39Z
Computational complexity of traffic hijacking under BGP and S-BGP
Chiesa, M.
Di Battista, G.
Patrignani, M.
Erlebach, Thomas
http://hdl.handle.net/2381/31661
2015-02-13T02:01:28Z
2015-02-12T15:21:43Z
Title: Computational complexity of traffic hijacking under BGP and S-BGP
Authors: Chiesa, M.; Di Battista, G.; Patrignani, M.; Erlebach, Thomas
Abstract: Harmful Internet hijacking incidents put in evidence how fragile the Border Gateway Protocol (BGP) is, which is used to exchange routing information between Autonomous Systems (ASes). As proved by recent research contributions, even S-BGP, the secure variant of BGP that is being deployed, is not fully able to blunt traffic attraction attacks. Given a traffic flow between two ASes, we study how difficult it is for a malicious AS to devise a strategy for hijacking or intercepting that flow. We show that this problem marks a sharp difference between BGP and S-BGP. Namely, while it is solvable, under reasonable assumptions, in polynomial time for the type of attacks that are usually performed in BGP, it is NP-hard for S-BGP. Our study has several by-products. E.g., we solve a problem left open in the literature, stating when performing a hijacking in S-BGP is equivalent to performing an interception.
2015-02-12T15:21:43Z
Approximation algorithms for disjoint st-paths with minimum activation cost
Alqahtani, Hasna Mohsen
Erlebach, Thomas
http://hdl.handle.net/2381/31648
2015-02-12T02:01:29Z
2015-02-11T13:28:34Z
Title: Approximation algorithms for disjoint st-paths with minimum activation cost
Authors: Alqahtani, Hasna Mohsen; Erlebach, Thomas
Abstract: In network activation problems we are given a directed or undirected graph G = (V,E) with a family {f (x, x) : (u,v) ∈ E} of monotone non-decreasing activation functions from D to {0,1}, where D is a constant-size domain. The goal is to find activation values x for all v ∈ V of minimum total cost Σ x such that the activated set of edges satisfies some connectivity requirements. Network activation problems generalize several problems studied in the network literature such as power optimization problems. We devise an approximation algorithm for the fundamental problem of finding the Minimum Activation Cost Pair of Node-Disjoint st-Paths (MA2NDP). The algorithm achieves approximation ratio 1.5 for both directed and undirected graphs. We show that a ρ-approximation algorithm for MA2NDP with fixed activation values for s and t yields a ρ-approximation algorithm for the Minimum Activation Cost Pair of Edge-Disjoint st-Paths (MA2EDP) problem. We also study the MA2NDP and MA2EDP problems for the special case |D| = 2.
2015-02-11T13:28:34Z
Multi-Type Display Calculus for Propositional Dynamic Logic
Frittella, S.
Greco, G.
Kurz, Alexander
Palmigiano, A.
http://hdl.handle.net/2381/31644
2015-02-12T02:01:31Z
2015-02-11T11:12:31Z
Title: Multi-Type Display Calculus for Propositional Dynamic Logic
Authors: Frittella, S.; Greco, G.; Kurz, Alexander; Palmigiano, A.
Abstract: We introduce a multi-type display calculus for Propositional Dynamic
Logic (PDL). This calculus is complete w.r.t. PDL, and enjoys Belnap-style
cut-elimination and subformula property.
2015-02-11T11:12:31Z
A Multi-type Display Calculus for Dynamic Epistemic Logic
Frittella, S.
Greco, G.
Kurz, Alexander
Palmigiano, A.
Sikimić, V.
http://hdl.handle.net/2381/31643
2015-02-12T02:01:30Z
2015-02-11T11:06:46Z
Title: A Multi-type Display Calculus for Dynamic Epistemic Logic
Authors: Frittella, S.; Greco, G.; Kurz, Alexander; Palmigiano, A.; Sikimić, V.
Abstract: In the present paper, we introduce a multi-type display calculus for dynamic
epistemic logic, which we refer to as Dynamic Calculus. The displayapproach
is suitable to modularly chart the space of dynamic epistemic logics
on weaker-than-classical propositional base. The presence of types endows
the language of the Dynamic Calculus with additional expressivity, allows
for a smooth proof-theoretic treatment, and paves the way towards a general
methodology for the design of proof systems for the generality of dynamic
logics, and certainly beyond dynamic epistemic logic. We prove that
the Dynamic Calculus adequately captures Baltag-Moss-Solecki’s dynamic
epistemic logic, and enjoys Belnap-style cut elimination.
2015-02-11T11:06:46Z
Establishing the Source Code Disruption Caused by Automated Remodularisation Tools
Hall, M.
Khojaye, Muhammad
Walkinshaw, Neil
McMinn, P.
http://hdl.handle.net/2381/31618
2015-02-06T02:01:58Z
2015-02-05T14:45:08Z
Title: Establishing the Source Code Disruption Caused by Automated Remodularisation Tools
Authors: Hall, M.; Khojaye, Muhammad; Walkinshaw, Neil; McMinn, P.
Editors: Poshyvanik, D.; Zaidman, A.
Abstract: Current software remodularisation tools only operate on abstractions of a software system. In this paper, we investigate the actual impact of automated remodularisation on source code using a tool that automatically applies remodularisations as refactorings. This shows us that a typical remodularisation (as computed by the Bunch tool) will require changes to thousands of lines of code, spread throughout the system (typically no code files remain untouched). In a typical multi-developer project this presents a serious integration challenge, and could contribute to the low uptake of such tools in an industrial context. We relate these findings with our ongoing research into techniques that produce iterative commit friendly code changes to address this problem.
2015-02-05T14:45:08Z
A Proof-Theoretic Semantic Analysis of Dynamic Epistemic Logic
Frittella, S.
Greco, G.
Kurz, Alexander H.
Palmigiano, A.
Sikimić, V.
http://hdl.handle.net/2381/31596
2015-02-05T02:01:33Z
2015-02-04T16:21:31Z
Title: A Proof-Theoretic Semantic Analysis of Dynamic Epistemic Logic
Authors: Frittella, S.; Greco, G.; Kurz, Alexander H.; Palmigiano, A.; Sikimić, V.
Editors: Aucher, G.; Hjortland, O.; Roy, O.
Abstract: The present article provides an analysis of the existing proof systems for dynamic epistemic logic from the viewpoint of proof-theoretic semantics. Dynamic epistemic logic is one of the best-known members of a family of logical systems that have been successfully applied to diverse scientific disciplines, but the proof-theoretic treatment of which presents many difficulties. After an illustration of the proof-theoretic semantic principles most relevant to the treatment of logical connectives, we turn to illustrating the main features of display calculi, a proof-theoretic paradigm that has been successfully employed to give a proof-theoretic semantic account of modal and substructural logics. Then, we review some of the most significant proposals of proof systems for dynamic epistemic logics, and we critically reflect on them in the light of the previously introduced proof-theoretic semantic principles. The contributions of the present article include a generalization of Belnap's cut-elimination metatheorem for display calculi, and a revised version of the display-style calculus D.EAK [30]. We verify that the revised version satisfies the previously mentioned proof-theoretic semantic principles, and show that it enjoys cut-elimination as a consequence of the generalized metatheorem.
2015-02-04T16:21:31Z
Minimum activation cost node-disjoint paths in graphs with bounded treewidth
Alqahtani, Hasna Mohsen
Erlebach, Thomas
http://hdl.handle.net/2381/31524
2015-01-31T02:01:32Z
2015-01-30T12:01:13Z
Title: Minimum activation cost node-disjoint paths in graphs with bounded treewidth
Authors: Alqahtani, Hasna Mohsen; Erlebach, Thomas
Abstract: In activation network problems we are given a directed or undirected graph G = (V,E) with a family {f uv : (u,v) ∈ E} of monotone non-decreasing activation functions from D2 to {0,1}, where D is a constant-size subset of the non-negative real numbers, and the goal is to find activation values xv for all v ∈ V of minimum total cost ∑ v ∈ V x v such that the activated set of edges satisfies some connectivity requirements. We propose algorithms that optimally solve the minimum activation cost of k node-disjoint st-paths (st-MANDP) problem in O(tw ((5 + tw)|D|)2tw + 2|V|3) time and the minimum activation cost of node-disjoint paths (MANDP) problem for k disjoint terminal pairs (s 1,t 1),…,(s k ,t k ) in O(tw ((4 + 3tw)|D|)2tw + 2|V|) time for graphs with treewidth bounded by tw.
2015-01-30T12:01:13Z
Nominal Lambda Calculus
Nebel, Frank
http://hdl.handle.net/2381/31396
2015-01-09T02:01:53Z
2015-01-08T15:07:38Z
Title: Nominal Lambda Calculus
Authors: Nebel, Frank
Abstract: Since their introduction, nominal techniques have been widely applied in computer
science to reason about syntax of formal systems involving name-binding operators.
The work in this thesis is in the area of “nominal" type theory, or more precisely the
study of “nominal" simple types.
We take Nominal Equational Logic (NEL), which augments equational logic with
freshness judgements, as our starting point to introduce the Nominal Lambda Calculus
(NLC), a typed lambda calculus that provides a simple form of name-dependent
function types. This is a key feature of NLC, which allows us to encode freshness in
a novel way.
We establish meta-theoretic properties of NLC and introduce a sound model theoretic
semantics. Further, we introduce NLC[A], an extension of NLC that captures
name abstraction and concretion, and provide pure NLC[A] with a strongly
normalising and confluent βη-reduction system.
A property that has not yet been studied for “nominal" typed lambda calculi is
completeness of βη-conversion for a nominal analogue of full set-theoretic hierarchies.
Aiming towards such a result, we analyse known proof techniques and identify various
issues. As an interesting precursor, we introduce full nominal hierarchies and
demonstrate that completeness holds for βη-conversion of the ordinary typed lambda
calculus.
The notion of FM-categories was developed by Ranald Clouston to demonstrate
that FM-categories correspond precisely to NEL-theories. We augment FM-categories
with equivariant exponentials and show that they soundly model NLC-theories. We
then outline why NLC is not complete for such categories, and discuss in detail an
approach towards extending NLC which yields a promising framework from which we
aim to develop a future (sound and complete) categorical semantics and a categorical
type theory correspondence.
Moreover, in pursuit of a categorical conservative extension result, we study (enriched/
internal) Yoneda isomorphisms for “nominal" categories and some form of
“nominal" gluing.
2015-01-08T15:07:38Z
CMMI-CM compliance checking of formal BPMN models using Maude
El-Saber, Nissreen A. S.
http://hdl.handle.net/2381/31390
2015-01-09T02:02:03Z
2015-01-08T12:29:00Z
Title: CMMI-CM compliance checking of formal BPMN models using Maude
Authors: El-Saber, Nissreen A. S.
Abstract: From the perspective of business process improvement models, a business process
which is compliant with best practices and standards (e.g. CMMI) is necessary for defining
almost all types of contracts and government collaborations. In this thesis, we propose
a formal pre-appraisal approach for Capability Maturity Model Integration (CMMI)
compliance checking based on a Maude-based formalization of business processes in
Business Process Model and Notation (BPMN). The approach can be used to assess
the designed business process compliance with CMMI requirements as a step leading
to a full appraisal application. In particular, The BPMN model is mapped into Maude,
and the CMMI compliance requirements are mapped into Linear Temporal Logic (LTL)
then the Maude representation of the model is model checked against the LTL properties
using the Maude’s LTL model checker.
On the process model side, BPMN models may include structural issues that hinder
their design. In this thesis, we propose a formal characterization and semantics specification
of well-formed BPMN processes using the formalization of rewriting logic (Maude)
with a focus on data-based decision gateways and data objects semantics. Our formal
specification adheres to the BPMN standards and enables model checking using Maude’s
LTL model checker. The proposed semantics is formally proved to be sound based on the
classical workflow model soundness definition. On the compliance requirements side,
CMMI configuration management process is used as a source of compliance requirements
which then are mapped through compliance patterns into LTL properties. Model
checking results of Maude based implementation are explained based on a compliance
grading scheme. Examples of CMMI configuration management processes are used to
illustrate the approach.
2015-01-08T12:29:00Z
Management concerns in service-driven applications
Alghamdi, Ahmed Musfer
http://hdl.handle.net/2381/30107
2014-12-16T02:17:29Z
2014-12-15T10:36:12Z
Title: Management concerns in service-driven applications
Authors: Alghamdi, Ahmed Musfer
Abstract: With the abundance of functionally-similar Web-Services, the offered or agreed-on qualities are becoming decisive factors in attracting private as well as corporate customers to a given service, among all others. Nevertheless, the state-of-art in handling qualities, in this emerging service paradigm, remains largely bound to the aspects of technology and their standards (e.g. time-response, availability, throughputs). However, current approaches still ignore capital domain-based business qualities and management concerns (e.g. customer profiles, business deadlines). The main objective of this thesis is to leverage the handling of quality and management issues in service-driven business applications toward the intuitive business level supported by a precise and flexible conceptualisation. Thus, instead of addressing qualities using just rigid IT-SLA (service-level agreements) as followed by Web Services technology and standards, we propose to cope with more abstract and domain-dependent and adaptive qualities in an intuitive, yet conceptual, manner. The approach is centred on evolving business rules and policies for management, with a clean separation of functionalities as specific rules. At the conceptual level, we propose specialised architectural connectors called management laws that we also separate from coordination laws for functionality issues. We further propose a smooth and compliant mapping of the conceptualisation toward service technology, using existing rule-based standards.
2014-12-15T10:36:12Z
Flexibo : language and its application to static analysis
Zhou, Jianguo
http://hdl.handle.net/2381/30106
2014-12-16T02:17:28Z
2014-12-15T10:36:12Z
Title: Flexibo : language and its application to static analysis
Authors: Zhou, Jianguo
Abstract: This thesis introduces a new object-based language FlexibO to support prototype development paradigm and more importantly, program static analysis. FlexibO offers extreme flexibility and hence enables developers to write programs that contain rich information for further analysis and optimization. FlexibO interpreter's seamless integration with Java (including direct access to Java classes and methods and direct inheritance of Java classes) makes it a suitable tool for fast prototype software development. FlexibO's extreme flexibility allows developers to redefine the behavior of program evaluation by overriding its default evaluation method. This mechanism can be used to translate FlexibO to other efficient languages. In this thesis we design a translator in FlexibO to translate Bulk-Synchronous Parallel specifications (expressed in FlexibO) to executable C pro grams linked with BSPLib. Before translation, the tool first checks syntax and type, then statically analyzes potential communication conflicts, and finally generates C code. The translation process can accurately analyze primitive commands but require approximation (using abstract interpretation) for more advanced commands such as loops. The appropriateness of the translator and the associated static analysis can be formally analyzed using the technique of normal form.
2014-12-15T10:36:12Z
Automatic presentations of groups and semigroups
Oliver, Graham
http://hdl.handle.net/2381/30105
2014-12-16T02:17:27Z
2014-12-15T10:36:10Z
Title: Automatic presentations of groups and semigroups
Authors: Oliver, Graham
Abstract: Effectively deciding the satisfiability of logical sentences over structures is an area well-studied in the case of finite structures. There has been growing work towards considering this question for infinite structures. In particular the theory of automatic structures, considered here, investigates structures representable by finite automata. The closure properties of finite automata lead naturally to algorithms for deciding satisfiability for some logics. The use of finite automata to investigate infinite structures has been inspired by the interplay between the theory of finite automata and the theory of semigroups. This inspiration has come in particular from the theory of automatic groups and semigroups, which considers (semi)groups with regular sets of normal forms over their generators such that generator-composition is also regular. The work presented here is a contribution to the foundational problem for automatic structures: given a class of structures, classify those members that have an automatic presentation. The classes considered here are various interesting subclasses of the class of finitely generated semigroups, as well as the class of Cayley Graphs of groups. Although similar, the theories of automatic (semi)groups and automatic presentation differ in their construction. A classification for finitely generated groups allows a direct comparison of the theory of automatic presentations with the theory of automatic groups.
2014-12-15T10:36:10Z
Formal languages and the irreducible word problem in groups
Fonseca, Ana
http://hdl.handle.net/2381/30103
2014-12-16T02:17:23Z
2014-12-15T10:36:09Z
Title: Formal languages and the irreducible word problem in groups
Authors: Fonseca, Ana
Abstract: There exist structural classifications of groups with a regular, one-counter or context-free word problem. Following on from this, the main object of the work presented here has been the irreducible word problem of a group, a notion introduced by Haring-Smith, who denned it as the subset of the word problem consisting of the non-empty words which have no non-empty proper subword equal to the identity. He proved that the groups with a finite irreducible word problem with respect to some group generating set are exactly the plain groups.;We know that the class of groups with a context-free irreducible word problem is a proper subclass of the virtually free groups. We look at direct products of finitely generated free groups by finite groups and also at the plain groups and consider their irreducible word problems with respect to minimal group generating sets. We prove that, of all the direct products of the infinite cyclic group by a non-trivial finite group, only Z x Z2 and Z x Z 3 have context-free irreducible word problem (and only with respect to a few group generating sets). We also exhibit a plain group that has context-free irreducible word problem with respect to every minimal group generating set.;Looking at the direct products of finitely generated free groups by non-trivial finite groups, we have found that the only irreducible word problem that is one-counter is that of Z x Z2 with respect to the canonical group generating set.;As for irreducible word problems lying in classes of languages above context-free, on one hand, we prove that having a recursive irreducible word problem is equivalent to having a recursive word problem. On the other hand, we prove that, while there are groups such that the fact that their irreducible word problem is recursively enumerable implies that they are recursive, that is not always the case.
2014-12-15T10:36:09Z
Optimization problems in communication networks
Mihalak, Matus
http://hdl.handle.net/2381/30104
2014-12-16T02:17:26Z
2014-12-15T10:36:09Z
Title: Optimization problems in communication networks
Authors: Mihalak, Matus
Abstract: We study four problems arising in the area of communication networks. The minimum-weight dominating set problem in unit disk graphs asks, for a given set D of weighted unit disks, to find a minimum-weight subset D' âŠ† D such that the disks D' intersect all disks D. The problem is NP-hard and we present the first constant-factor approximation algorithm. Applying our techniques to other geometric graph problems, we can obtain better (or new) approximation algorithms. The network discovery problem asks for a minimum number of queries that discover all edges and non-edges of an unknown network (graph). A query at node v discovers a certain portion of the network. We study two different query models and show various results concerning the complexity, approximability and lower bounds on competitive ratios of online algorithms. The OVSF-code assignment problem deals with assigning communication codes (nodes) from a complete binary tree to users. Users ask for codes of a certain depth and the codes have to be assigned such that (i) no assigned code is an ancestor of another assigned code and (ii) the number of (previously) assigned codes that have to be reassigned (in order to satisfy (i)) is minimized. We present hardness results and several algorithms (optimal, approximation, online and fixed-parameter tractable). The joint base station scheduling problem asks for an assignment of users to base stations (points in the plane) and for an optimal colouring of the resulting conflict graph: user u with its assigned base station b is in conflict with user v, if a disk with center at 6, and u on its perimeter, contains v. We study the complexity, and present and analyse optimal, approximation and greedy algorithms for general and various special cases.
2014-12-15T10:36:09Z
Categories of containers
Abbott, Michael Gordon
http://hdl.handle.net/2381/30102
2014-12-16T02:17:23Z
2014-12-15T10:36:09Z
Title: Categories of containers
Authors: Abbott, Michael Gordon
Abstract: This thesis develops a new approach to the theory of datatypes based on separating data and storage resulting in a class of datatype called a container. The extension of a container is a functor which can be regarded as a generalised polynomial functor in type variables. A representation theorem allows every natural transformation between container functors to be represented as a unique pair of morphisms in a category.;Under suitable assumptions on the ambient category container functors are closed under composition, limits, coproducts and the construction of initial algebras and final coalgebras. These closure properties allow containers to provide a functorial semantics for an important class of polymorphic types including the strictly positive types.;Since polymorphic functions between functorial polymorphic types correspond to natural transformations, every polymorphic function can be represented as a container morphism; this simplifies reasoning about such functions and provides a framework for developing concepts of generic programming.;Intuitionistic well-founded trees or W-types are the initial algebras of container functors in one parameter; the construction of the initial algebra of a container in more than one parameter leads to the solution of a problem left incomplete by earlier work of Dybjer.;We also find that containers provide a suitable framework to define the derivative of a functor as a kind of linear exponential. We show that the use of containers is essential for this approach.;The theory is developed in the context of a fairly general category to allow for a wide choice of applications. We use the language of dependent type theory to develop the theory of containers in an arbitrary extensive locally cartesian closed category; much of the development in this thesis can also be generalised to display map categories. We develop the appropriate internal language and its interpretation in a category with families.
2014-12-15T10:36:09Z
Alternative approaches to optophonic mappings
Capp, Michael.
http://hdl.handle.net/2381/30101
2014-12-16T02:17:22Z
2014-12-15T10:36:08Z
Title: Alternative approaches to optophonic mappings
Authors: Capp, Michael.
Abstract: This thesis presents a number of modifications to a blind aid, known as the video optophone, which enables a blind user to more readily interpret that local environment for enhanced mobility and navigation. Versions of this form of blind aid are generally both difficult to use and interpret, and are therefore inadequate for safe mobility. The reason for this severe problem lies in the complexity and excessive bandwidth of the optophonic output after the conversion from scene-to-sound.;The work herein describes a number of modifications that can be applied to the current optophonic process to make more efficient use of the limited bandwidth provided by the auditory system when converting scene images to sound. Various image processing and stereo techniques have been employed to artificially emulate the human visual system through the use of depth maps that successfully fade out the quantity of relatively unimportant image features, whilst emphasising the more significant regions such as nearby obstacles.;A series of experiments was designed to test these various modifications to the optophonic mapping by studying important factors of mobility and subject response whilst going about everyday life. The devised system, labelled DeLIA for the Detection, Location, Identification, and Avoidance (or Action) of obstacles, provided a means for gathering statistical data on users' interpretation of the optophonic output. An analysis of this data demonstrated a significant improvement when using the stereo cartooning technique, developed as part of this work, over the more conventional plain image as an input to an optophonic mapping from scene-to-sound.;Lastly, conclusions were drawn from the results, which indicated that the use of a stereo depth map as an input to a video optophone would improve its usefulness as an aid to general mobility. For the purposes of detecting and determining text or similar detail, either a plain unmodified image or some form of edge (depth) image were found to produce the best results.
2014-12-15T10:36:08Z
Multimodal human-computer interaction for enhancing customers’ decision-making and experience on B2C e-commerce websites
Al Sokkar, Abdullah Ahmad Musa
http://hdl.handle.net/2381/29330
2014-12-10T02:01:46Z
2014-12-09T11:49:14Z
Title: Multimodal human-computer interaction for enhancing customers’ decision-making and experience on B2C e-commerce websites
Authors: Al Sokkar, Abdullah Ahmad Musa
Abstract: The main aim of this thesis was to identify, complement and refine the factors that contribute to users’ intention to purchase, satisfaction and attitude toward using a particular B2C online environment, as well as the causal relationships between these factors. A systematic literature review on Information System (IS), Market Research, and User Experience (UX), which has informed the design and development of a pilot study, has been conducted. Results have led to the conception of an online shopping decision-making (OSDM) model called ‘Episodic UX Model on Decision-Making’ (EUX-DM). It has been developed by integrating the established Technology Acceptance Model (TAM) as well as Information System Success Model (ISSM), and emerging UX models, and Expectation-Confirmation Theory (ECT). Results from analysing 305 responses to the web-based questionnaire aimed to evaluate EUX-DM verified its validity. In addition, after investigating the users’ preferences for the possible modifications related to the use of visual avatar in a particular B2C e-Commerce website for information presentation, another research focus has been placed on identifying the real conversational functions and their related communicational behaviour in designing male and female visual avatars’ facial expressions and body gestures. Following this, four different types of information presentations have been developed to be used in a contrived B2C online shopping environment, namely: (i) 2D static graphical and textual information, (ii) non-expressive avatars, (iii) avatars with facial expressions, (iv) and avatars with facial expressions and body gestures information presentations. Consequently, these information presentations were empirically investigated through two experimental studies. The outcomes of these studies indicated that the gender of the avatar and participants were found to be insignificant factors for any of the measured qualities, and the use of visual avatars with animated facial expressions and body gestures positively influenced customers’ usage attitude, intention to purchase and satisfaction.
2014-12-09T11:49:14Z
Lem : Reusable engineering of real-world semantics
Mulligan, Dominic P.
Gray, Kathryn E.
Sewell, Peter
Owens, Scott
Ridge, Tom
http://hdl.handle.net/2381/29328
2014-12-10T02:01:48Z
2014-12-09T10:33:34Z
Title: Lem : Reusable engineering of real-world semantics
Authors: Mulligan, Dominic P.; Gray, Kathryn E.; Sewell, Peter; Owens, Scott; Ridge, Tom
Abstract: Recent years have seen remarkable successes in rigorous engineering: using mathematically rigorous semantic models (not just idealised calculi) of real-world processors, programming languages, protocols, and security mechanisms, for testing, proof, analysis, and design. Building these models is challenging, requiring experimentation, dialogue with vendors or standards bodies, and validation; their scale adds engineering issues akin to those of programming to the task of writing clear and usable mathematics. But language and tool support for specification is lacking. Proof assistants can be used but bring their own difficulties, and a model produced in one, perhaps requiring many person-years effort and maintained over an extended period, cannot be used by those familiar with another. We introduce Lem, a language for engineering reusable large-scale semantic models. The Lem design takes inspiration both from functional programming languages and from proof assistants, and Lem definitions are translatable into OCaml for testing, Coq, HOL4, and Isabelle/HOL for proof, and LaTeX and HTML for presentation. This requires a delicate balance of expressiveness, careful library design, and implementation of transformations - akin to compilation, but subject to the constraint of producing usable and human-readable code for each target. Lem's effectiveness is demonstrated by its use in practice. © 2014 ACM.
2014-12-09T10:33:34Z
Simple, efficient, sound and complete combinator parsing for all context-free grammars, using an oracle
Ridge, Tom
http://hdl.handle.net/2381/29327
2014-12-10T02:01:48Z
2014-12-09T10:20:37Z
Title: Simple, efficient, sound and complete combinator parsing for all context-free grammars, using an oracle
Authors: Ridge, Tom
Abstract: Parsers for context-free grammars can be implemented directly and naturally in a functional style known as “combinator parsing”, using recursion following the structure of the grammar rules. Traditionally parser combinators have struggled to handle all features of context-free grammars, such as left recursion.
Previous work introduced novel parser combinators that could be used to parse all context-free grammars. A parser generator built using these combinators was proved both sound and complete in the HOL4 theorem prover. Unfortunately the performance was not as good as other parsing methods such as Earley parsing.
In this paper, we build on this previous work, and combine it in novel ways with existing parsing techniques such as Earley parsing. The result is a sound-and-complete combinator parsing library that can handle all context-free grammars, and has good performance.
Description: timestamp: Tue, 09 Sep 2014 10:57:11 +0200 biburl: http://dblp.uni-trier.de/rec/bib/conf/sle/Ridge14 bibsource: dblp computer science bibliography, http://dblp.org
2014-12-09T10:20:37Z
On the Synthesis of Choreographies
Lange, Julien
http://hdl.handle.net/2381/29310
2014-12-05T02:01:48Z
2014-12-04T12:10:48Z
Title: On the Synthesis of Choreographies
Authors: Lange, Julien
Abstract: The theories based on session types stand out as effective methodologies
to specify and verify properties of distributed systems. A key result in the area shows the
suitability of choreography languages and session types as a basis for a choreography-driven
methodology for distributed software development. The methodology it advocates
is as follows: a team of programmers designs a global view of the interactions to be
implemented (i.e., a choreography), then the choreography is projected onto each role.
Finally, each program implementing one or more roles in the choreography is validated
against its corresponding projection(s).
This is an ideal methodology but it may not always be possible to design one set of
choreographies that will drive the overall development of a distributed system. Indeed,
software needs maintenance, specifications may evolve (sometimes also during the development),
and issues may arise during the implementation phase. Therefore, there is a
need for an alternative approach whereby it is possible to infer a choreography from local
behavioural specifications (i.e., session types).
We tackle the problem of synthesising choreographies from local behavioural specifications
by introducing a type system which assigns – if possible – a choreography to
set of session types. We demonstrate the importance of obtaining a choreography from
local specifications through two applications. Firstly, we give three algorithms and a
methodology to help software designers refine a choreography into a global assertion,
i.e., a choreography decorated with logical formulae specifying senders’ obligations and
receivers’ requirements. Secondly, we introduce a formal model for distributed systems
where each participant advertises its requirements and obligations as behavioural contracts
(in the form of session types), and where multiparty sessions are started when a set
of contracts allows to synthesise a choreography.
2014-12-04T12:10:48Z
User Activity Recognition through Software Sensors
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/29228
2015-01-01T02:45:05Z
2014-10-30T10:28:23Z
Title: User Activity Recognition through Software Sensors
Authors: Reiff-Marganiec, Stephan
Abstract: Context-aware systems are an instance of the ubiquitous or pervasive computing vision. They sense the users’ physical and virtual surrounding to identify the best system support for that user and adapt the system behaviour accordingly. The overall architecture of a context aware system can be broken into a number of logical aspects: gathering context data, storing the data, deriving knowledge through reasoning and mining and retrieving that knowledge to finally adapting system behaviours. Context is anything characterizing the environment of the user – their location, the ambient temperature, the people they are with, their current activity and some even consider the user’s mood. Traditionally context information has been gathered through the use of hardware sensors, such as GPS sensors or smart badges for locations and there has been work to track user’s eye movements at their desk to see which application they are using. However, determining the activity of a user has shown to be elusive to being sensed with hardware sensors. As users use web services more frequently they are exchanging messages with the services through the SOAP protocol. SOAP messages contain data, which is valuable if gathered and interpreted right – especially as this data can be shedding information on the activity of a user that goes beyond “sitting at the computer and typing”. We propose a complimentary sensor technology through the use of software sensors. The software sensors are essentially based on monitoring SOAP messages and inserting data for further reasoning and querying into a semantic context model. In this paper we consider details of extracting the data from SOAP messages in a non-obstructive way and show a solution to map the data from a SOAP message to our OWL ontology model automatically. On the latter, we specifically explain the methodology to map from SOAP messages to an existing structure of knowledge.
Description: The file associated with this record is embargoed until 18 months after the date of publication. The final published version may be available through the links above.
2014-10-30T10:28:23Z
Succinct indices for range queries with applications to orthogonal range maxima
Farzan, Arash
Munro, J. Ian
Raman, Rajeev
http://hdl.handle.net/2381/29206
2014-10-29T02:01:32Z
2014-10-28T10:40:48Z
Title: Succinct indices for range queries with applications to orthogonal range maxima
Authors: Farzan, Arash; Munro, J. Ian; Raman, Rajeev
Abstract: We consider the problem of preprocessing N points in 2D, each endowed with a priority, to answer the following queries: given a axis-parallel rectangle, determine the point with the largest priority in the rectangle. Using the ideas of the effective entropy of range maxima queries and succinct indices for range maxima queries, we obtain a structure that uses O(N) words and answers the above query in O(logN loglogN) time. This a direct improvement of Chazelle's result from 1985 [10] for this problem - Chazelle required O(N/ε) words to answer queries in O((logN)[superscript 1+ε]) time for any constant ε > 0.
2014-10-28T10:40:48Z
Succinct representations of ordinal trees
Raman, Rajeev
Rao, S. Srinivasa
http://hdl.handle.net/2381/29205
2014-10-29T02:01:31Z
2014-10-28T10:33:36Z
Title: Succinct representations of ordinal trees
Authors: Raman, Rajeev; Rao, S. Srinivasa
Abstract: We survey succinct representations of ordinal, or rooted, ordered trees. Succinct representations use space that is close to the appropriate information-theoretic minimum, but support operations on the tree rapidly, usually in O(1) time.
2014-10-28T10:33:36Z
On probabilistic models for uncertain sequential pattern mining
Muzammal, Muhammad
Raman, Rajeev
http://hdl.handle.net/2381/29204
2014-10-30T09:16:46Z
2014-10-28T10:26:52Z
Title: On probabilistic models for uncertain sequential pattern mining
Authors: Muzammal, Muhammad; Raman, Rajeev
Editors: Cao, L.; Feng, Y.; Zhong, J.
Abstract: We study uncertainty models in sequential pattern mining. We consider situations where there is uncertainty either about a source or an event. We show that both these types of uncertainties could be modelled using probabilistic databases, and give possible-worlds semantics for both. We then describe ”interestingness” criteria based on two notions of frequentness (previously studied for frequent itemset mining) namely expected support [C. Aggarwal et al. KDD’09;Chui et al., PAKDD’07,’08] and probabilistic frequentness [Bernecker et al., KDD’09]. We study the interestingness criteria from a complexity-theoretic perspective, and show that in case of source-level uncertainty, evaluating probabilistic frequentness is #P-complete, and thus no polynomial time algorithms are likely to exist, but evaluate the interestingness predicate in polynomial time in the remaining cases.
2014-10-28T10:26:52Z
Encodings for range selection and top-k queries
Grossi, Roberto
Iacono, John
Navarro, Gonzalo
Raman, Rajeev
Rao, S. Srinivasa
http://hdl.handle.net/2381/29203
2014-10-29T02:01:30Z
2014-10-28T10:16:57Z
Title: Encodings for range selection and top-k queries
Authors: Grossi, Roberto; Iacono, John; Navarro, Gonzalo; Raman, Rajeev; Rao, S. Srinivasa
Abstract: We study the problem of encoding the positions the top-k elements of an array A[1..n] for a given parameter 1 ≤ k ≤ n. Specifically, for any i and j, we wish create a data structure that reports the positions of the largest k elements in A[i..j] in decreasing order, without accessing A at query time. This is a natural extension of the well-known encoding range-maxima query problem, where only the position of the maximum in A[i..j] is sought, and finds applications in document retrieval and ranking. We give (sometimes tight) upper and lower bounds for this problem and some variants thereof.
2014-10-28T10:16:57Z
Discovery of network properties with all-shortest-paths queries
Bilo, Davide
Erlebach, Thomas Rainer
Mihalak, Matus
Widmayer, Peter
http://hdl.handle.net/2381/29198
2014-10-24T01:01:32Z
2014-10-23T15:40:02Z
Title: Discovery of network properties with all-shortest-paths queries
Authors: Bilo, Davide; Erlebach, Thomas Rainer; Mihalak, Matus; Widmayer, Peter
Editors: Shvartsman, A. A.; Felber, P.
Abstract: We consider the problem of discovering properties (such as the diameter) of an unknown network G(V,E) with a minimum number of queries. Initially, only the vertex set V
of the network is known. Information about the edges and non-edges of the network can be obtained
by querying nodes of the network. A query at a node q∈V returns the
union of all shortest paths from q to all other nodes in V. We study the
problem as an online problem - an algorithm does not initially know the
edge set of the network, and has to decide where to make the next query
based on the information that was gathered by previous queries. We
study how many queries are needed to discover the diameter, a minimal
dominating set, a maximal independent set, the minimum degree, and
the maximum degree of the network. We also study the problem of deciding with a minimum number of queries whether the network is 2-edge or
2-vertex connected. We use the usual competitive analysis to evaluate the
quality of online algorithms, i.e., we compare online algorithms with optimum offline algorithms. For all properties except maximal independent
set and 2-vertex connectivity we present and analyze online algorithms.
Furthermore we show, for all the aforementioned properties, that "many"
queries are needed in the worst case. As our query model delivers more
information about the network than the measurement heuristics that are
currently used in practise, these negative results suggest that a similar
behavior can be expected in realistic settings, or in more realistic models
derived from the all-shortest-paths query model.
2014-10-23T15:40:02Z
Asympotically optimal encodings for range selection
Navarro, Gonzalo
Raman, Rajeev
Satti, Srinivasa Rao
http://hdl.handle.net/2381/29193
2014-12-15T02:45:04Z
2014-10-22T14:00:04Z
Title: Asympotically optimal encodings for range selection
Authors: Navarro, Gonzalo; Raman, Rajeev; Satti, Srinivasa Rao
Abstract: We consider the problem of preprocessing an array A[1..n] to answer range selection and range top-k queries. Given a query interval [i..j] and a value k, the former query asks for the position of the kth largest value in A[i..j], whereas the latter asks for the positions of all the k largest values in A[i..j]. We consider the encoding version of the problem, where A is not available at query time, and an upper bound kappa on k, the rank that is to be selected, is given at construction time. We obtain data structures with asymptotically optimal size and query time on a RAM model with word size Θ(lg n) : our structures use O(n lg kappa) bits and answer range selection queries in time O(1+ lg k / lg lg n) and range top-k queries in time O(k), for any k ≤ kappa.
Description: The file associated with this record is embargoed until the date of the conference.
2014-10-22T14:00:04Z
Mining state-based models from proof corpora
Gransden, Thomas
Walkinshaw, Neil
Raman, Rajeev
http://hdl.handle.net/2381/29141
2014-10-07T14:59:44Z
2014-10-07T14:53:42Z
Title: Mining state-based models from proof corpora
Authors: Gransden, Thomas; Walkinshaw, Neil; Raman, Rajeev
Abstract: Interactive theorem provers have been used extensively to reason about various software/hardware systems and mathematical theorems. The key challenge when using an interactive prover is finding a suitable sequence of proof steps that will lead to a successful proof requires a significant amount of human intervention. This paper presents an automated technique that takes as input examples of successful proofs and infers an Extended Finite State Machine as output. This can in turn be used to generate proofs of new conjectures. Our preliminary experiments show that the inferred models are generally accurate (contain few false-positive sequences) and that representing existing proofs in such a way can be very useful when guiding new ones.
2014-10-07T14:53:42Z
Dynamizing succinct tree representations
Joannou, Stelios
Raman, Rajeev
http://hdl.handle.net/2381/29103
2014-09-19T01:01:28Z
2014-09-18T08:51:47Z
Title: Dynamizing succinct tree representations
Authors: Joannou, Stelios; Raman, Rajeev
Abstract: We consider succinct, or space-efficient, representations of ordinal trees. Representations exist that take 2n + o(n) bits to represent a static n-node ordinal tree - close to the information-theoretic minimum - and support navigational operations in O(1) time on a RAM model; and some implementations have good practical performance. The situation is different for dynamic ordinal trees. Although there is theoretical work on succinct dynamic ordinal trees, there is little work on the practical performance of these data structures. Motivated by applications to representing XML documents, in this paper, we report on a preliminary study on dynamic succinct data structures. Our implementation is based on representing the tree structure as a sequence of balanced parentheses, with navigation done using the min-max tree of Sadakane and Navarro (SODA '10). Our implementation shows promising performance for update and navigation, and our findings highlight two issues that we believe will be important to future implementations: the difference between the finger model of (say) Farzan and Munro (ICALP '09) and the parenthesis model of Sadakane and Navarro, and the choice of the balanced tree used to represent the min-max tree.
2014-09-18T08:51:47Z
A model for supporting electrical engineering with e-learning
Akaslan, Dursun
http://hdl.handle.net/2381/29066
2014-09-09T01:01:29Z
2014-09-08T14:27:39Z
Title: A model for supporting electrical engineering with e-learning
Authors: Akaslan, Dursun
Abstract: The overall goal of this research work was developing and evaluating a model for supporting electrical engineering with e-learning. The model development was based on the survey data collected from representative teachers and students in Turkey whereas the model evaluation was conducted in the relevant HEIs in Turkey and the United Kingdom. To develop the model, the study investigated the attitudes of representative key stakeholders towards e-learning in Turkey by administrating questionnaires and interviews with teachers and students. Then the responses of the teachers and students were compared. Based on the results, I proposed a model with a multi-dimensional approach to e-learning: (1) self-directed learning by studying e-book, (2) self-assessment by solving e-exercises, (3) teacher-directed learning by attending classroom sessions as an integral part of the blended learning (4) teacher-assessment by solving e-exercises, (5) computer-directed learning by playing e-games and (6) computer-assessment by solving e-exercises.
To evaluate the applicability of the model in different conditions, a case-control study was conducted to determine whether the model had the intended effect on the participating students in HEIs in Turkey and the United Kingdom. As the result of the case-control study, the effects of e-learning, blended learning and traditional learning were verified. However, there were significant differences among the groups. The overall scores indicated that e-learning and blended learning was more effective as compared to the traditional learning. The results of our study indicated that the knowledge increase in e-learners seemed to be gradual because they tended to study daily by completing each activity on time. However, the traditional learners did not have the same pattern because they usually did not read the core text and did not solve e-exercise regularly before the classroom sessions. The results of pre-placement, post-placement tests and middle tests also justified these assumptions.
2014-09-08T14:27:39Z
Compressed representation of XML documents with rapid navigation
Kharabsheh, Mohammad Kamel Ahmad
http://hdl.handle.net/2381/29062
2014-09-06T01:01:27Z
2014-09-05T15:30:29Z
Title: Compressed representation of XML documents with rapid navigation
Authors: Kharabsheh, Mohammad Kamel Ahmad
Abstract: XML(Extensible Markup Language) is a language used in data representation and
storage, and transmission and manipulation of data. Excessive memory consumption
is an important challenge when representing XML documents in main memory.
Document Object Model (DOM) APIs are used in a processing level that provides
access to all parts of XML documents through the navigation operations. Although
DOM serves as a a general purpose tool that can be used in different applications,
it has high memory cost particularly if using na¨ıve. The space usage of DOM has
been reduced significantly while keeping fast processing speeds, by use of succinct
data structures in SiXDOM [1]. However, SiXDOM does not explore in depth XML
data compression principles to improve in-memory space usage. Such XML data
compression techniques have been proven to be very effective in on-disk compression
of XML document. In this thesis we propose a new approach to represent XML
documents in-memory using XML data compression ideas to further reduce space
usage while rapidly supporting operations of the kind supported by DOM.
Our approach is based upon a compression method [2] which represents an XML
document as a directed acyclic graph (DAG) by sharing common subtrees. However,
this approach does not permit the representation of attributes and textual data,
and furthermore, a naive implementation of this idea gives very poor space usage
relative to other space-efficient DOM implementations [1]. In order to realise the
potential of this compression method as an in-memory representation, a number
of optimisations are made by application of succinct data structures and variablelength
encoding. Furthermore, a framework for supporting attribute and textual
data nodes is introduced. Finally, we propose a novel approach to representing the
textual data using Minimal Perfect Hashing(MPH).
We have implemented our ideas in a software library called DAGDOMand performed
extensive experimental evaluation on a number of standard XML files. DAGDOM
yields a good result and we are able to obtain significant space reductions over existing
space-efficient DOM implementations (typically 2 to 5 times space reduction),
with very modest degradations in CPU time for navigational operations.
2014-09-05T15:30:29Z
Backward analysis via over-approximate abstraction and under-approximate subtraction
Piterman, Nir
Bakhirkin, Alexey
Berdine, Josh
http://hdl.handle.net/2381/28950
2014-09-12T13:24:10Z
2014-06-26T14:09:45Z
Title: Backward analysis via over-approximate abstraction and under-approximate subtraction
Authors: Piterman, Nir; Bakhirkin, Alexey; Berdine, Josh
Abstract: We propose a novel approach for computing weakest liberal safe preconditions of programs. The standard approaches, which call for either under-approximation of a greatest fixed point, or complementation of a least fixed point, are often difficult to apply successfully. Our approach relies on a different decomposition of the weakest precondition of loops. We exchange the greatest fixed point for the computation of a least fixed point above a recurrent set, instead of the bottom element. Convergence is achieved using over-approximation, while in order to maintain soundness we use an under-approximating logical subtraction operation. Unlike general complementation, subtraction more easily allows for increased precision in case its arguments are related. The approach is not restricted to a specific abstract domain and we use it to analyze programs using the abstract domains of intervals and of 3-valued structures.
Description: The file associated with this record is embargoed until 12 months after the date of publication. The final published version may be available through the links above.
2014-06-26T14:09:45Z
Mining sequential patterns from probabilistic databases
Muzammal, Muhammad
Raman, Rajeev
http://hdl.handle.net/2381/28949
2014-08-06T10:59:39Z
2014-06-26T13:15:31Z
Title: Mining sequential patterns from probabilistic databases
Authors: Muzammal, Muhammad; Raman, Rajeev
Abstract: This paper considers the problem of sequential pattern mining (SPM) in
probabilistic databases. Specifically, we consider SPM in situations where there is uncertainty
in associating an event with a source, model this kind of uncertainty in the probabilistic
database framework and consider the problem of enumerating all sequences
whose expected support is sufficiently large. We give an algorithm based on dynamic
programming to compute the expected support of a sequential pattern. Next, we propose
three algorithms for mining sequential patterns from probabilistic databases. The
first two algorithms are based on the candidate generation framework – one each based
on a breadth-first (similar to GSP) and a depth-first (similar to SPAM) exploration
of the search space. The third one is based on the pattern growth framework (similar
to PrefixSpan). We propose optimizations that mitigate the effects of the expensive
dynamic programming computation step. We give an empirical evaluation of the probabilistic
SPM algorithms and the optimizations, and demonstrate the scalability of the
algorithms in terms of CPU time and the memory usage. We also demonstrate the
effectiveness of the probabilistic SPM framework in extracting meaningful sequences in
the presence of noise.
Description: The file associated with this record is embargoed until 12 months after the date of publication. The final published version may be available through the links above.
2014-06-26T13:15:31Z
Design-by-contract for software architectures
Poyias, Kyriakos
http://hdl.handle.net/2381/28924
2014-06-17T01:01:58Z
2014-06-16T15:40:37Z
Title: Design-by-contract for software architectures
Authors: Poyias, Kyriakos
Abstract: We propose a design by contract (DbC) approach to specify and maintain architectural
level properties of software. Such properties are typically relevant in the design
phase of the development cycle but may also impact the execution of systems. We give a
formal framework for specifying software architectures (and their refi nements) together
with contracts that architectural con figurations abide by. In our framework, we can
specify that if an architecture guarantees a given pre- condition and a refi nement rule
satisfi es a given contract, then the refi ned architecture will enjoy a given post-condition.
Methodologically, we take Architectural Design Rewriting (ADR) as our architectural
description language. ADR is a rule-based formal framework for modelling (the
evolution of) software architectures. We equip the recon figuration rules of an ADR
architecture with pre- and post-conditions expressed in a simple logic; a pre-condition
constrains the applicability of a rule while a post-condition specifi es the properties
expected of the resulting graphs. We give an algorithm to compute the weakest precondition
out of a rule and its post-condition. Furthermore, we propose a monitoring
mechanism for recording the evolution of systems after certain computations, maintaining
the history in a tree-like structure. The hierarchical nature of ADR allows us to
take full advantage of the tree-like structure of the monitoring mechanism. We exploit
this mechanism to formally defi ne new rewriting mechanisms for ADR reconfi guration
rules. Also, by monitoring the evolution we propose a way of identifying which part of
a system has been a ffected when unexpected run-time behaviours emerge. Moreover,
we propose a methodology that allows us to select which rules can be applied at the
architectural level to reconfigure a system so to regain its architectural style when it
becomes compromised by unexpected run-time recon figurations.
2014-06-16T15:40:37Z
A structured approach to VO reconfigurations through Policies
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/28881
2014-05-31T01:01:22Z
2014-05-30T10:52:19Z
Title: A structured approach to VO reconfigurations through Policies
Authors: Reiff-Marganiec, Stephan
Abstract: One of the strength of Virtual Organisations is their ability to dynamically and rapidly adapt in response
to changing environmental conditions. Dynamic adaptability has been studied in other system
areas as well and system management through policies has crystallized itself as a very prominent solution
in system and network administration. However, these areas are often concerned with very
low-level technical aspects. Previous work on the APPEL policy language has been aimed at dynamically
adapting system behaviour to satisfy end-user demands and – as part of STPOWLA – APPEL
was used to adapt workflow instances at runtime. In this paper we explore how the ideas of APPEL
and STPOWLA can be extended from workflows to the wider scope of Virtual Organisations. We will
use a Travel Booking VO as example.
2014-05-30T10:52:19Z
Maintaining transactional integrity in long running workflow service : a policy-driven framework
Reiff-Marganiec, Stephan
Ali, Manar S.
http://hdl.handle.net/2381/28880
2014-05-30T01:01:22Z
2014-05-29T15:48:08Z
Title: Maintaining transactional integrity in long running workflow service : a policy-driven framework
Authors: Reiff-Marganiec, Stephan; Ali, Manar S.
Abstract: This chapter presents a framework to provide autonomous handling of long running transactions based
on dependencies which are derived from the workflow. Business Processes naturally involve long running
activities and require transactional behaviour across them. This framework presents a solution for forward
recovery from errors by automatic application of compensation to executing instances of workflows. The
mechanism is based on propagation of failures through a recursive hierarchical structure of transaction
components (nodes and execution paths). The authors discuss a transaction management system that is
implemented as a reactive system controller, where system components change their states based on rules
in response to triggering of events, such as activation, failure, force-fail, completion, or compensation
events. One notable feature of the model is the distinction of vital and non-vital components, allowing
the process designer to express the cruciality of activities in the workflow with respect to the business
logic. Another novel feature is that in addition to dependencies arising from the structure of the workflow,
the approach also permits the workflow designer to specify additional dependencies which will also be
enforced. Thus, the authors introduce new techniques and architectures supporting enterprise integration
solutions that cater to the dynamics of business needs. The approach is implemented through workflow
actions executed by services and allows management of faults through a policy-driven framework.
2014-05-29T15:48:08Z
Encoding range minima and range top-2 queries
Davoodi, Pooya
Navarro, Gonzalo
Raman, Rajeev
Rao, S. Srinivasa
http://hdl.handle.net/2381/28856
2014-05-29T01:01:22Z
2014-05-28T10:49:40Z
Title: Encoding range minima and range top-2 queries
Authors: Davoodi, Pooya; Navarro, Gonzalo; Raman, Rajeev; Rao, S. Srinivasa
Abstract: We consider the problem of encoding range minimum queries (RMQs): given an array A[1..n] of distinct totally ordered values, to pre-process A and create a data structure that can answer the query RMQ(i,j), which returns the index containing the smallest element in A[i..j], without access to the array A at query time. We give a data structure whose space usage is 2n+o(n) bits, which is asymptotically optimal for worst-case data, and answers RMQs in O(1) worst-case time. This matches the previous result of Fischer and Heun, but is obtained in a more natural way. Furthermore, our result can encode the RMQs of a random array A in 1.919n+o(n) bits in expectation, which is not known to hold for Fischer and Heun’s result. We then generalize our result to the encoding range top-2 query (RT2Q) problem, which is like the encoding RMQ problem except that the query RT2Q(i,j) returns the indices of both the smallest and second smallest elements of A[i..j]. We introduce a data structure using 3.272n+o(n) bits that answers RT2Qs in constant time, and also give lower bounds on the effective entropy of the RT2Q problem.
2014-05-28T10:49:40Z
Optimal indexes for sparse bit vectors
Golynski, Alexander
Orlandi, Alessio
Raman, Rajeev
Rao, S. Srinivasa
http://hdl.handle.net/2381/28854
2014-05-28T01:01:25Z
2014-05-27T10:19:32Z
Title: Optimal indexes for sparse bit vectors
Authors: Golynski, Alexander; Orlandi, Alessio; Raman, Rajeev; Rao, S. Srinivasa
Abstract: We consider the problem of supporting rank and select operations on a bit vector of length m with n 1-bits. The problem is considered in the succinct index model, where the bit vector is stored in "read-only" memory and an additional data structure, called the index is created during pre-processing to help answer the above queries. We give asymptotically optimal density-sensitive trade-offs, involving both m and n, that relate the size of the index to the number of accesses to the bit vector (and processing time) needed to answer the above queries. The results are particularly interesting for the case where n=o(m).
2014-05-27T10:19:32Z
An empirical evaluation of extendible arrays
Joannou, Stelios
Raman, Rajeev
http://hdl.handle.net/2381/28738
2014-04-10T01:01:14Z
2014-04-09T10:40:44Z
Title: An empirical evaluation of extendible arrays
Authors: Joannou, Stelios; Raman, Rajeev
Editors: Pardalos, PM; Rebennack, S
Abstract: We study the performance of several alternatives for implementing extendible arrays, which allow random access to elements stored
in them, whilst allowing the arrays to be grown and shrunk. The study
not only looks at the basic operations of grow/shrink and accessing data, but also the effects of memory fragmentation on performance.
Description: The final publication is
available at link.springer.com
2014-04-09T10:40:44Z
Cell-cycle regulation of NOTCH signaling during C. elegans vulval development
Nusser-Stein, Stefanie
Beyer, Antje
Rimann, Ivo
Adamczyk, Magdalene
Piterman, Nir
Hajnal, Alex
Fisher, Jasmin
http://hdl.handle.net/2381/28643
2014-03-08T02:01:51Z
2014-03-07T13:50:41Z
Title: Cell-cycle regulation of NOTCH signaling during C. elegans vulval development
Authors: Nusser-Stein, Stefanie; Beyer, Antje; Rimann, Ivo; Adamczyk, Magdalene; Piterman, Nir; Hajnal, Alex; Fisher, Jasmin
Abstract: C. elegans vulval development is one of the best‐characterized systems to study cell fate specification during organogenesis. The detailed knowledge of the signaling pathways determining vulval precursor cell (VPC) fates permitted us to create a computational model based on the antagonistic interactions between the epidermal growth factor receptor (EGFR)/RAS/MAPK and the NOTCH pathways that specify the primary and secondary fates, respectively. A key notion of our model is called bounded asynchrony, which predicts that a limited degree of asynchrony in the progression of the VPCs is necessary to break their equivalence. While searching for a molecular mechanism underlying bounded asynchrony, we discovered that the termination of NOTCH signaling is tightly linked to cell‐cycle progression. When single VPCs were arrested in the G1 phase, intracellular NOTCH failed to be degraded, resulting in a mixed primary/secondary cell fate. Moreover, the G1 cyclins CYD‐1 and CYE‐1 stabilize NOTCH, while the G2 cyclin CYB‐3 promotes NOTCH degradation. Our findings reveal a synchronization mechanism that coordinates NOTCH signaling with cell‐cycle progression and thus permits the formation of a stable cell fate pattern.
2014-03-07T13:50:41Z
Faster temporal reasoning for infinite-state programs
Piterman, Nir
Cook, Byron
Khlaaf, Heidy
http://hdl.handle.net/2381/28591
2014-02-20T14:18:38Z
2014-02-20T14:08:53Z
Title: Faster temporal reasoning for infinite-state programs
Authors: Piterman, Nir; Cook, Byron; Khlaaf, Heidy
Abstract: In many model checking tools that support temporal logic, performance is hindered by redundant reasoning performed in the presence of nested temporal operators. In particular, tools supporting the state-based temporal logic CTL often symbolically partition the system's state space using the sub-formulae of the input temporal formula. This can lead to repeated work when tools are applied to infinite-state programs, as often the characterization of the state-spaces for nearby program locations are similar and interrelated. In this paper, we describe a new symbolic procedure for CTL verification of infinite-state programs. Our procedure uses the structure of the program's control-flow graph in combination with the nesting of temporal operators in order to optimize reasoning performed during symbolic model checking. An experimental evaluation against competing tools demonstrates that our approach not only gains orders-of-magnitude performance speed improvement, but allows for scalability of temporal reasoning for larger programs.
2014-02-20T14:08:53Z
Strongly complete logics for coalgebras
Kurz, Alexander
Rosicky, Jiri
http://hdl.handle.net/2381/28587
2014-02-14T10:52:56Z
2014-02-14T10:52:40Z
Title: Strongly complete logics for coalgebras
Authors: Kurz, Alexander; Rosicky, Jiri
Abstract: Coalgebras for a functor model different types of transition systems in a uniform way. This paper focuses on a uniform account of finitary logics for set-based coalgebras. In particular, a general construction of a logic from an arbitrary set-functor is given and proven to be strongly complete under additional assumptions. We proceed in three parts. Part I argues that sifted colimit preserving functors are those functors that preserve universal algebraic structure. Our main theorem here states that a functor preserves sifted colimits if and only if it has a finitary presentation by operations and equations. Moreover, the presentation of the category of algebras for the functor is obtained compositionally from the presentations of the underlying category and of the functor. Part II investigates algebras for a functor over ind-completions and extends the theorem of J{'o}nsson and Tarski on canonical extensions of Boolean algebras with operators to this setting. Part III shows, based on Part I, how to associate a finitary logic to any finite-sets preserving functor T. Based on Part II we prove the logic to be strongly complete under a reasonable condition on T.
2014-02-14T10:52:40Z
Completeness for the coalgebraic cover modality
Kupke, Clemens
Kurz, Alexander
Venema, Yde
http://hdl.handle.net/2381/28586
2014-02-14T10:41:31Z
2014-02-14T10:40:06Z
Title: Completeness for the coalgebraic cover modality
Authors: Kupke, Clemens; Kurz, Alexander; Venema, Yde
Abstract: We study the finitary version of the coalgebraic logic introduced by L.Moss. The syntax of this logic, which is introduced uniformly with respect to a coalgebraic type functor, required to preserve weak pullbacks, extends that of classical propositional logic with a so-called coalgebraic cover modality depending on the type functor. Its semantics is defined in terms of a categorically defined relation lifting operation. As the main contributions of our paper we introduce a derivation system, and prove that it provides a sound and complete axiomatization for the collection of coalgebraically valid inequalities. Our soundness and completeness proof is algebraic, and we employ Pattinson's stratification method, showing that our derivation system can be stratified in countably many layers, corresponding to the modal depth of the formulas involved. In the proof of our main result we identify some new concepts and obtain some auxiliary results of independent interest. We survey properties of the notion of relation lifting, induced by an arbitrary but fixed set functor. We introduce a category of Boolean algebra presentations, and establish an adjunction between it and the category of Boolean algebras. Given the fact that our derivation system involves only formulas of depth one, it can be encoded as a endo-functor on Boolean algebras. We show that this functor is finitary and preserves embeddings, and we prove that the Lindenbaum-Tarski algebra of our logic can be identified with the initial algebra for this functor.
2014-02-14T10:40:06Z
Activity awareness in context-aware systems using software sensors
Pathan, Kamran Taj
http://hdl.handle.net/2381/28379
2013-11-09T02:02:34Z
2013-11-08T15:49:07Z
Title: Activity awareness in context-aware systems using software sensors
Authors: Pathan, Kamran Taj
Abstract: Context-aware systems being a component of ubiquitous or pervasive computing environment sense the users’ physical and virtual surrounding to adapt their behaviour accordingly. To achieve activity context tracking devices are common practice. Service Oriented Architecture is based on collections of services that communicate with each other. The communication between users and services involves data that can be used to sense the activity context of the user. SOAP is a simple protocol to let applications exchange their information over the web. Semantic Web provides standards to express the relationship between data to allow machines to process data more intelligently.
This work proposes an approach for supporting context-aware activity sensing using software sensors. The main challenges in the work are specifying context information in a machine processable form, developing a mechanism that can understand the data extracted from exchanges of services, utilising the data extracted from these services, and the architecture that supports sensing with software sensors. To address these issues, we have provided a bridge to combine the traditional web services with the semantic web technologies, a knowledge structure that supports the activity context information in the context-aware environments and mapping methods that extract the data out of exchanges occurring between user and services and map it into a context model. The Direct Match, the Synonym Match and the Hierarchical Match methods are developed to put the extracted data from services to the knowledge structure.
This research will open doors to further develop automated and dynamic context-aware systems that can exploit the software sensors to sense the activity of the user in the context-aware environments.
2013-11-08T15:49:07Z
Pure Type Systems with Corecursion on Streams: From Finite to Infinitary Normalisation
Severi, Paula
de Vries, Fer-Jan
http://hdl.handle.net/2381/28332
2013-10-29T02:02:06Z
2013-10-28T15:24:43Z
Title: Pure Type Systems with Corecursion on Streams: From Finite to Infinitary Normalisation
Authors: Severi, Paula; de Vries, Fer-Jan
Abstract: In this paper, we use types for ensuring that programs involving streams are well-behaved.We extend pure type systems with a type constructor for streams, a modal operator next and a fixed point operator for expressing corecursion. This extension is called Pure Type Systems with Corecursion (CoPTS). The typed lambda calculus for reactive programs defined by Krishnaswami and Benton can be obtained as a CoPTS. CoPTSs allow us to study a wide range of typed lambda calculi extended with corecursion using only one framework. In particular, we study this extension for the calculus of constructions which is the underlying formal language of Coq. We use the machinery of infinitary rewriting and formalise the idea of well-behaved programs using the concept of infinitary normalisation. The set of finite and infinite terms is defined as a metric completion. We establish a precise connection between the modal operator (• A) and the metric at a syntactic level by relating a variable of type (• A) with the depth of all its occurrences in a term. This syntactic connection between the modal operator and the depth is the key to the proofs of infinitary weak and strong normalisation.
2013-10-28T15:24:43Z