Slicing for modern program structures: a theory for eliminating irrelevant loops

Slicing is a program transformation technique with numerous applications, as it allows the user to focus on the parts of a program that are relevant for a given purpose. Ideally, the slice program should have the same termination properties as the original program, but to keep the slices manageable, it might be preferable to slice away loops that do not affect the values of relevant variables. This paper provides the first theoretical foundation to reason about non-termination insensitive slicing without assuming the presence of a unique end node. A slice is required to be closed under data dependence and under a recently proposed variant of control dependence, called weak order dependence. This allows a simulation-based correctness proof for a correctness criterion stating that the observational behavior of the original program must be a prefix of the behavior of the slice program.     

An alternative characterization of weak order dependence

Control dependence forms the basis for many program analyses, such as program slicing. Recent work on control dependence analysis has led to new definitions of dependence that can allow for reactive programs with their necessarily non-terminating computations. One important such definition is the definition of Weak Order Dependence, which was introduced to generalize classical control dependence for a Control Flow Graph (CFG) without end nodes. In this paper we show that for a CFG where all nodes are reachable from each other, weak order dependence can be expressed in terms of traditional control dependence where one node has been converted into an end node.     

A framework for modular ERDF ontologies

The success of the Semantic Web is impossible without any form of modularity, encapsulation, and access control. In an earlier paper, we extended RDF graphs with weak and strong negation, as well as derivation rules. The ERDF #n-stable model semantics of the extended RDF framework (ERDF) is defined, extending RDF(S) semantics. In this paper, we propose a framework for modular ERDF ontologies, called modular ERDF framework, which enables collaborative reasoning over a set of ERDF ontologies, while support for hidden knowledge is also provided. In particular, the modular ERDF stable model semantics of modular ERDF ontologies is defined, extending the ERDF #n-stable model semantics. Our proposed framework supports local semantics and different points of view, local closed-world and open-world assumptions, and scoped negation-as-failure. Several complexity results are provided.     

Why-provenance information for RDF,rules, and negation

The provenance (i.e., origins) of derived information on the Web is crucial in many applications to allow information quality assessment, trust judgments, accountability, as well as understanding the temporal and spatial status of the information. On the other hand, the inclusion of negative information in knowledge representation both in the form of negation-as-failure and explicit negation is also important to allow various forms of reasoning, provided that weakly negated information is associated with the sources (contexts) in which it holds. In this work, we consider collections of g-RDF ontologies, distributed over the web, along with a set of conflict statements expressing that information within a pair of g-RDF ontologies cannot be combined together for deriving new information. A g-RDF ontology is the combination of (i) a g-RDF graph G (i.e., a set of positive and strongly negated RDF triples, called g-RDF triples) and (ii) a g-RDF program P containing derivation rules with possibly both explicit and scoped weak negation. Information can be inferred through the g-RDF graphs or the derivation rules of the g-RDF ontologies, or through the RDFS derivation rules. We associate each derived grounded g-RDF triple [¬] p(s, o) with the set of names S of the g-RDF ontologies that contributed to its derivation. To achieve this, we define the provenance stable models of a g-RDF ontology collection. We show that our provenance g-RDF semantics faithfully extends RDFS semantics. Finally, we provide an algorithm based on Answer Set Programming that computes all provenance stable models of a g-RDF ontology collection and provides the answer to various kinds of queries. Various complexity results are provided.     

On temporal path conditions in dependence graphs

Program dependence graphs are a well-established device to represent possible information flow in a program. Path conditions in dependence graphs have been proposed to express more detailed circumstances of a particular flow; they provide precise necessary conditions for information flow along a path or chop in a dependence graph. Ordinary boolean path conditions, however, cannot express temporal properties, e.g. that for a specific flow it is necessary that some condition holds, and later another specific condition holds. In this contribution, we introduce temporal path conditions, which extend ordinary path conditions by temporal operators in order to express temporal dependencies between conditions for a flow. We present motivating examples, generation and simplification rules, application of model checking to generate witnesses for a specific flow, and a case study. We prove the following soundness property: if a temporal path condition for a path is satisfiable, then the ordinary boolean path condition for the path is satisfiable. The converse does not hold, indicating that temporal path conditions are more precise. An extended abstract of the present article appeared in the 2007 Proceedings of the Seventh IEEE International Working Conference on Source Code Analysis and Manipulation (SCAM 2007). The research of A. Lochbihler was partially supported by Deutsche Forschungsgemeinschaft, grant Sn11/9-1.     

Two-level grammar as an implementable metalanguage for axiomatic semantics

Two-level grammars can define the syntax and the operational semantics of programming languages and these definitions are directly executable by interpretation. In this paper it is shown that axiomatic semantics can also be defined using a two-level grammar with the result being a partially automatic program verification system accomplished within the framework of a language definition. These results imply that a programming language can be defined operationally and axiomatically together in complementary definitions as advocated by Hoare and Lauer. Because two-level grammars are executable, these complementary definitions accomplish a system for interpreting and verifying programs.     

Opacity of discrete event systems and its applications

In this paper, we investigate opacity of discrete event systems. We define two types of opacities: strong opacity and weak opacity. Given a general observation mapping, a language is strongly opaque if all strings in the language are confused with some strings in another language and it is weakly opaque if some strings in the language are confused with some strings in another language. We show that security and privacy of computer systems and communication protocols can be investigated in terms of opacity. In particular, two important properties in security and privacy, namely anonymity and secrecy, can be studied as special cases of opacity. We also show that by properly specifying the languages and the observation mapping, three important properties of discrete event systems, namely observability, diagnosability, and detectability, can all be reformulated as opacity. Thus, opacity has a wide range of applications. Also in this paper we provide algorithms for checking strong opacity and weak opacity for systems described by regular languages and having a generalized projection as the observation mapping.     

Detecting value-based scalar dependence

Precise value-based data dependence analysis for scalars is useful for advanced compiler optimizations. The new method presented here for flow and output dependence uses Factored Use and Def chains (FUD chains), our interpretation and extension of Static Single Assignment. It is precise with respect to conditional control flow and dependence vectors. Our method detects dependences which are independent with respect to arbitrary loop nesting, as well as loop-carried dependences. A loop-carried dependence is further classified as being carried from the previous iteration, with distance 1, or from any previous iteration, with direction <. This precision cannot be achieved by traditional analysis, such as dominator information or reaching definitions. To compute anti- and input dependence, we use Factored Redef-Use chains, which are related to FUD chains. We are not aware of any prior work which explicitly deals with scalar data dependence utilizing a sparse graph representation. A preliminary version of this paper appeared in theSeventh Anual Workshop on Languages and Compilers for Parallel Computing, August 1994. Supported in part by NSF Grant CCR-9113885 and a grant from Intel Corporation and the Oregon Advanced Computing Institute.     

基于符号迁移图的互模拟验证算法

符号迁移图是传值进程的一种直观而简洁的语义表示模型，该模型由Hennessy和Lin首先提出，随后又被Lin推广至带赋值的符号迁移图，本文不但定义了符号迁移图各种版本（基／符号）的强操作语义和强互模拟，提出了相互的强互模拟算法，而且通过引入符号观察图和符号同余图，给出了其弱互模拟等价和观察同余的验证算法，给出并证明了了τ－循环和τ－边消去定理，在应用任何弱互模拟观察同余验证算法之前，均可利用这些定理对所给符号迁移图进行化简。     

Strong order equivalence

Recently, strong equivalence for Answer Set Programming has been studied intensively, and was shown to be beneficial for modular programming and automated optimization. In this paper we define the novel notion of strong order equivalence for logic programs with preferences (ordered logic programs). Based on this definition we give, for several semantics for preference handling, necessary and sufficient conditions for programs to be strongly order equivalent. These results allow us also to associate a so-called SOE structure to each ordered logic program, such that two ordered logic programs are strongly order equivalent if and only if their SOE structures coincide. We also present the relationships among the studied semantics with respect to strong order equivalence, which differs considerably from their relationships with respect to preferred answer sets. Furthermore, we study the computational complexity of several reasoning tasks associated to strong order equivalence. Finally, based on the obtained results, we present – for the first time – simplification methods for ordered logic programs.     

Strong Paraconsistency and the Basic Constructive Logic for an Even Weaker Sense of Consistency

In a standard sense, consistency and paraconsistency are understood as the absence of any contradiction and as the absence of the ECQ (‘E contradictione quodlibet’) rule, respectively. The concepts of weak consistency (in two different senses) as well as that of F-consistency have been defined by the authors. The aim of this paper is (a) to define alternative (to the standard one) concepts of paraconsistency in respect of the aforementioned notions of weak consistency and F-consistency; (b) to define the concept of strong paraconsistency; (c) to build up a series of strongly paraconsistent logics; (d) to define the basic constructive logic adequate to a rather weak sense of consistency. All logics treated in this paper are strongly paraconsistent. All of them are sound and complete in respect a modification of Routley and Meyer’s ternary relational semantics for relevant logics (no logic in this paper is relevant).     

Session types for safe Web service orchestration

We address the general problem of interaction safety in Web service orchestrations. By considering an essential subset of the BPEL orchestration language, we define SeB, a session based style of this subset. We discuss the formal semantics of SeB and present its main properties. We take a new approach to address the formal semantics which is based on a translation into so-called control graphs. Our semantics accounts for BPEL control links and addresses the static semantics that prescribes the valid usage of variables. We also provide the semantics of service configurations.During a session, a client and a service can engage in a complex series of interactions. By means of the provided semantics, we define precisely what is meant by interaction safety. We then introduce session types in order to prescribe the correct orderings of these interactions. Service providers must declare their provided and required session types. We define a typing algorithm that checks if a service orchestration behaves according to its declared provided and required types.Using a subtyping relation defined on session types, we show that any configuration of well-typed service partners with compatible session types are interaction safe, i.e., involved partners never receive unexpected messages.     

基于程序依赖图的静态BPEL程序切片技术

传统程序切片技术在计算BPEL程序切片时会产生切片不完备问题,为此,提出一种基于程序依赖图的BPEL静态程序切片技术。该技术根据BPEL语言的特点,通过建立BPEL程序依赖图,计算BPEL程序切片。案例分析表明,该技术能够获得更加全面的程序切片,从而可以帮助软件工程人员更好地测试、调试和维护BPEL程序。     

A non-standard semantics for program slicing and dependence analysis

We introduce a new non-strict semantics for a simple while language. We demonstrate that this semantics allows us to give a denotational definition of variable dependence and neededness, which is consistent with program slicing. Unlike other semantics used in variable dependence, our semantics is substitutive. We prove that our semantics is preserved by traditional slicing algorithms.     

Symbolic graphs for attributed graph constraints

In this paper we present a new class of graphs, called symbolic graphs, to define a new class of constraints on attributed graphs. In particular, in the first part of the paper, we study the category of symbolic graphs showing that it satisfies some properties, which are the basis for the work that we present in the second part of the paper, where we study how to reason with attributed graph constraints. More precisely, we define a set of inference rules, which are the instantiation of the inference rules defined in a previous paper, for reasoning about constraints on standard graphs, showing their soundness and (weak) completeness. Moreover, the proof of soundness and completeness is also an instantiation of the corresponding proof for standard graph constraints, using the categorical properties studied in the first part of the paper. Finally, we show that adding a new inference rule makes our system sound and strongly complete.     

Bundle event structures: A revised cpo approach

Bundle event structures equipped with a partial order ? have been used to give a true concurrency denotational semantics for LOTOS. This model has also been extended by time and stochastic information. Unfortunately it fails to yield a complete partial order (cpo) as we illustrate by an example.We propose a subset of all bundle event structures such that it forms a cpo. This subset is closed under the usual operators on bundle event structures. And as a consequence these operators are continuous. Therefore, this subset can be used to give a denotational semantics of LOTOS.     

Reducts of propositional theories,satisfiability relations,and generalizations of semantics of logic programs

Over the years, the stable-model semantics has gained a position of the correct (two-valued) interpretation of default negation in programs. However, for programs with aggregates (constraints), the stable-model semantics, in its broadly accepted generalization stemming from the work by Pearce, Ferraris and Lifschitz, has a competitor: the semantics proposed by Faber, Leone and Pfeifer, which seems to be essentially different. Our goal is to explain the relationship between the two semantics. Pearce, Ferraris and Lifschitz's extension of the stable-model semantics is best viewed in the setting of arbitrary propositional theories. We propose here an extension of the Faber–Leone–Pfeifer semantics, or FLP semantics, for short, to the full propositional language, which reveals both common threads and differences between the FLP and stable-model semantics. We use our characterizations of FLP-stable models to derive corresponding results on strong equivalence and on normal forms of theories under the FLP semantics. We apply a similar approach to define supported models for arbitrary propositional theories, and to study their properties.     

Fixed point theorems on fuzzy normed linear spaces

In this paper, definitions of strongly fuzzy convergent sequence, l-fuzzy weakly convergent sequence and l-fuzzy weakly compact set are given in a fuzzy normed linear space. The concepts of fuzzy normal structure, fuzzy non-expansive mapping, uniformly convex fuzzy normed linear space are introduced and fixed point theorems for fuzzy non-expansive mappings are proved.     

Satisfiability and containment of recursive SHACL

The Shapes Constraint Language (SHACL) is the recent W3C recommendation language for validating RDF data, by verifying certain shapes on graphs. Previous work has largely focused on the validation problem, while the standard decision problems of satisfiability and containment, crucial for design and optimisation purposes, have only been investigated for simplified versions of SHACL. Moreover, the SHACL specification does not define the semantics of recursively-defined constraints, which led to several alternative recursive semantics being proposed in the literature. The interaction between these different semantics and important decision problems has not been investigated yet. In this article we provide a comprehensive study of the different features of SHACL, by providing a translation to a new first-order language, called SCL, that precisely captures the semantics of SHACL. We also present MSCL, a second-order extension of SCL, which allows us to define, in a single formal logic framework, the main recursive semantics of SHACL. Within this language we also provide an effective treatment of filter constraints which are often neglected in the related literature. Using this logic we provide a detailed map of (un)decidability and complexity results for the satisfiability and containment decision problems for different SHACL fragments. Notably, we prove that both problems are undecidable for the full language, but we present decidable combinations of interesting features, even in the face of recursion.     

Strong equivalence of logic programs under the infinite-valued semantics

We consider the notion of strong equivalence [V. Lifschitz, D. Pearce, A. Valverde, Strongly equivalent logic programs, ACM Transactions on Computational Logic 2 (4) (2001) 526-541] of normal propositional logic programs under the infinite-valued semantics [P. Rondogiannis, W.W. Wadge, Minimum model semantics for logic programs with negation-as-failure, ACM Transactions on Computational Logic 6 (2) (2005) 441-467] (which is a purely model-theoretic semantics that is compatible with the well-founded one). We demonstrate that two such programs are strongly equivalent under the infinite-valued semantics if and only if they are logically equivalent in the corresponding infinite-valued logic. In particular, we show that strong equivalence of normal propositional logic programs is decidable, and more specifically coNP-complete. Our results have a direct implication for the well-founded semantics since, as we demonstrate, if two programs are strongly equivalent under the infinite-valued semantics, then they are also strongly equivalent under the well-founded semantics.