The Formal Semantics of Program Slicing for Non-Terminating Computations

Since the original development of program slicing in 1979 [.Weiser slices 1979.] there have been many attempts to define a suitable semantics which will precisely define the meaning of a slice. Particular issues include handling termination and non-termination, slicing non-terminating programs and slicing nondeterministic programs. In this paper we review and critique the main attempts to construct a semantics for slicing and present a new operational semantics which correctly handles slicing for non-terminating and nondeterministic programs. We also present a modified denotational semantics which we prove to be equivalent to the operational semantics. This provides programmers with two different methods to prove the correctness of a slice or a slicing algorithm, and means that the program transformation theory and FermaT transformation system, developed over the last 25 years of research, and which has proved so successful in analysing terminating programs, can now be applied to non-terminating interactive programs

A general algebra of business rules for heterogeneous systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A wide spectrum type system for transformation theory

One of the most difficult tasks a programmer can be confronted with is the migration of a legacy system. Usually, these systems are unstructured, poorly documented and contain complex program logic. The reason for this, in most cases, is an emphasis on raw performance rather than on clean and structured code as well as a long period of applying quick fixes and enhancements rather than doing a proper software reengineering process including a full redesign during major enhancements. Nowadays, the old programming paradigms are becoming an increasingly serious problem. It has been identified that 90% of the costs of a typical software system arise in the maintenance phase. Many companies are simply too afraid of changing their software infrastructure and prefer to continue with principles like "never touch a running system". These companies experience growing pressure to migrate their legacy systems onto newer platforms because the maintenance of such systems is expensive and dangerous as the risk of losing vital parts of sources code or its documentation increases drastically over time. The FermaT transformation system has shown the ability to automatically or semi-automatically restructure and abstract legacy code within a special intermediate language called WSL (Wide Spectrum Language). Unfortunately, the current transformation process only supports the migration of assembler as WSL lacks the ability to handle data types properly. The data structures in assembler are currently directly translated into C data types which involves many assumptional “hard coded” conversions. The absence of an adequate type system for WSL caused several flaws for the whole transformation process and limits its abilities significantly. The main aim of the presented research is to tackle these problems by investigating and formulating how a type system can contribute to a safe and reliable migration of legacy systems. The described research includes the definition of key aspects of type related problems in the FermaT migration process and how to solve them with a suitable type system approach. Since software migration often includes a change in programming language the type system for WSL has to be able to support various type system approaches including the representation of all relevant details to avoid assumptions. This is especially difficult as most programming languages are designed for a special purpose which means that their possible programming constructs and data types differ significantly. This ranges from languages with simple type systems whose program sare prone to unintended side-effects, to languages with strict type systems which are constrained n their flexibility. It is important to include as many type related details as necessary to avoid making assumptions during language to language translation. The result of the investigation is a novel multi layered type system specifically designed to satisfy the needs of WSL for a sophisticated solution without imposing too many limitations on its abilities. The type system has an adjustable expressiveness, able to represent a wide spectrum of typing approaches ranging from weak typing which allows direct memory access and down casting, via very strict typing with a high diversity of data types to object oriented typing which supports encapsulation and data hiding. Looking at the majority of commercial relevant statically typed programming languages, two fundamental properties of type strictness and safety can be identified. A type system can be either weakly or strongly typed and may or may not allow unsafe features such as direct memory access. Each layer of the Wide Spectrum Type System has a different combination of these properties. The approach also includes special Type System Transformations which can be used to move a given WSL program among these layers. Other emphasised key features are explicit typing and scalability. The whole approach is based on a sound mathematical foundation which assures correctness and integrates seamlessly into the present mathematical definition of WSL. The type system is formally introduced to WSL by constructing an attribute grammar for the language. Type checking and type inference are used to annotate the Abstract Syntax Tree of a given WSL program with type derivations which can be used to reveal and indicate possible typing errors or to infer types if the program did not feature explicit type declarations in the first place. Notable in this approach is also the fact that object orientation is introduced to a procedural programming language without the introduction of new semantics. It is shown that object orientation can be introduced just by adjusting type checking rules and adding some syntactical notations. The approach was implemented and tested on two case studies. The thesis describes and discusses both cases in detail and shows how a migration which ignores type systems could accidentally introduce errors due to assumptions during translation. Both case studies use all important aspects of the approach, Including type transformations and object identification. The thesis finalises by summarising the whole work, identifying limitations, presenting future perspectives and drawing conclusion

Constraint based program transformation theory

Software Migration Lt

Provably Correct Derivation of Algorithms Using FermaT

The transformational programming method of algorithm derivation starts with a formal specification of the result to be achieved, plus some informal ideas as to what techniques will be used in the implementation. The formal specification is then transformed into an implementation, by means of correctness-preserving refinement and transformation steps, guided by the informal ideas. The transformation process will typically include the following stages: (1) Formal specification (2) Elaboration of the specification, (3) Divide and conquer to handle the general case (4) Recursion introduction, (5) Recursion removal, if an iterative solution is desired, (6) Optimisation, if required. At any stage in the process, sub-specifications can be extracted and transformed separately. The main difference between this approach and the invariant based programming approach (and similar stepwise refinement methods) is that loops can be introduced and manipulated while maintaining program correctness and with no need to derive loop invariants. Another difference is that at every stage in the process we are working with a correct program: there is never any need for a separate "verification" step. These factors help to ensure that the method is capable of scaling up to the development of large and complex software systems. The method is applied to the derivation of a complex linked list algorithm and produces code which is over twice as fast as the code written by Donald Knuth to solve the same problem

Slicing techniques applied to architectural analysis of legacy software

Tese de doutoramento em Informática (ramo de conhecimento em Fundamentos da Computação)Program understanding is emerging as a key concern in software engineering. In a situation in which the only quality certificate of the running software artifact still is life-cycle endurance, customers and software producers are little prepared to modify or improve running code. However, faced with so risky a dependence on legacy software, managers are more and more prepared to spend resources to increase confidence on - i.e., the level of understanding of - their (otherwise untouchable) code. In fact the technological and economical relevance of legacy software as well as the complexity of their re-engineering entails the need for rigour. Addressing such a scenario, this thesis advocates the use of direct source code analysis for both the process of understanding and transformation of software systems. In particular, the thesis focuses on the development and application of slicing techniques at both the “micro" and “macro" structural levels of software. The former, deals with fine-grained structures of programs, slicing operating over elementary program entities, such as types, variables or procedure identifiers. The latter, on the other hand, addresses architectural issues and interaction modes across modules, components or services upon which a system is decomposed. At the \micro" level this thesis delves into the problem of slicing functional programs, a paradigm that is gaining importance and was generally neglected by the slicing community. Three different approaches to functional slicing are proposed, accompanied by the presentation of the HaSlicer application, a software tool developed as a proof-of-concept for some of the ideas discussed. A comparison between the three approaches, their practical application and the motivational aspects for keeping investigating new functional slicing processes are also discussed. Slicing at a \macro" level is the theme of the second part of this thesis, which addresses the problem of extracting from source code the system's coordination model which governs interaction between its components. This line of research delivers two approaches for abstracting software systems coordination models, one of the most vital structures for software architectural analysis. Again, a software tool – CoordInspector – is introduced as a proof-of-concept.A compreensão de sistemas de software reveste-se de uma cada vez maior importância no campo da engenharia de software. Numa situação em que a única garantia de funcionamento dos diversos componentes de software reside apenas na metodologia de desenvolvimento adoptada, tanto clientes bem como produtores de software encontram-se pouco preparados para modificar ou melhorar os seus programas. No entanto, face a uma tão grande dependência em relação ao código legado, os gestores estão cada vez mais receptivos a gastar recursos de forma a aumentar a confiança - i.e., o nível de compreensão - dos seus (de outra forma intocáveis) programas. De facto, a relevância tecnológica e económica do software legado bem como a complexidade associada à sua reengenharia provocam uma urgente necessidade de rigor. Tendo este cenário como contexto, esta tese advoga o uso de uma análise directa de código fonte com o objectivo de compreender e transformar sistemas de software. Em particular, esta tese debruça-se sobre o desenvolvimento e a aplicação de técnicas de slicing aos níveis “micro" e “macro" das estruturas de software. A análise efectuada ao nível “micro" lida com estruturas de programas de pequena granularidade, onde o slicing opera sobre entidades elementares dos programas, tais como tipos, variáveis ou identificadores de procedimentos. Por outro lado, o nível de análise “macro" aborda questões arquitecturais, tais como as interacção entre módulos, componentes ou serviços sobre os quais um sistema de software pode ser decomposto. Ao nível “micro", esta tese aborda o problema de efectuar slicing a programas funcionais, um paradigma que se reveste de uma cada vez maior importância e o qual tem sido negligenciado pela comunidade de slicing. Neste sentido, esta tese apresenta três diferentes abordagens ao slicing funcional, acompanhadas pela apresentação da aplicação HaSlicer, uma ferramenta de software desenvolvida como prova de conceito para algumas das ideias expostas. No decorrer da apresentação destas propostas de abordagem ao slicing funcional, efectua-se ainda uma comparação entre os diversos processos, as suas aplicações práticas bem como os aspectos motivacionais que levaram à investigação de novos processos de slicing funcional. As operações de slicing ao nível “macro" constituem o tema da segunda parte desta tese, onde se aborda o problema específico da extracção de arquitecturas de sistemas de software. Neste sentido, são desenvolvidas duas abordagens distintas para a abstracção do modelo de coordenação de um sistema de software, o que constitui uma das mais vitais estruturas para a análise de sistemas de software. Mais uma vez, é apresentada uma ferramenta de software – CoordInspector – como prova de conceito.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/19127/200

EG-ICE 2021 Workshop on Intelligent Computing in Engineering

The 28th EG-ICE International Workshop 2021 brings together international experts working at the interface between advanced computing and modern engineering challenges. Many engineering tasks require open-world resolutions to support multi-actor collaboration, coping with approximate models, providing effective engineer-computer interaction, search in multi-dimensional solution spaces, accommodating uncertainty, including specialist domain knowledge, performing sensor-data interpretation and dealing with incomplete knowledge. While results from computer science provide much initial support for resolution, adaptation is unavoidable and most importantly, feedback from addressing engineering challenges drives fundamental computer-science research. Competence and knowledge transfer goes both ways

EG-ICE 2021 Workshop on Intelligent Computing in Engineering

The 28th EG-ICE International Workshop 2021 brings together international experts working at the interface between advanced computing and modern engineering challenges. Many engineering tasks require open-world resolutions to support multi-actor collaboration, coping with approximate models, providing effective engineer-computer interaction, search in multi-dimensional solution spaces, accommodating uncertainty, including specialist domain knowledge, performing sensor-data interpretation and dealing with incomplete knowledge. While results from computer science provide much initial support for resolution, adaptation is unavoidable and most importantly, feedback from addressing engineering challenges drives fundamental computer-science research. Competence and knowledge transfer goes both ways

Computer Aided Verification

This open access two-volume set LNCS 10980 and 10981 constitutes the refereed proceedings of the 30th International Conference on Computer Aided Verification, CAV 2018, held in Oxford, UK, in July 2018. The 52 full and 13 tool papers presented together with 3 invited papers and 2 tutorials were carefully reviewed and selected from 215 submissions. The papers cover a wide range of topics and techniques, from algorithmic and logical foundations of verification to practical applications in distributed, networked, cyber-physical, and autonomous systems. They are organized in topical sections on model checking, program analysis using polyhedra, synthesis, learning, runtime verification, hybrid and timed systems, tools, probabilistic systems, static analysis, theory and security, SAT, SMT and decisions procedures, concurrency, and CPS, hardware, industrial applications