Showing papers on "Operational semantics published in 1995"

The Syntax and Semantics of μCRL

Abstract: A simple specification language based on CRL (Common Representation Language)and therefore called μCRL (micro CRL) is proposed. It has been developed to study processes with data. So the language contains only basic constructs with an easy semantics. To obtain executability, effective μCRL has been defined. In effective μCRL equivalence between closed data-terms is decidable and the operational behaviour is finitely branching and computable. This makes effective μCRL a good platform for tooling activities.

Knowledge of Meaning: An Introduction to Semantic Theory

Abstract: Current textbooks in formal semantics are all versions of, or introductions to, the same paradigm in semantic theory: Montague Grammar. Knowledge of Meaning is based on different assumptions and a different history. It provides the only introduction to truth- theoretic semantics for natural languages, fully integrating semantic theory into the modern Chomskyan program in linguistic theory and connecting linguistic semantics to research elsewhere in cognitive psychology and philosophy. As such, it better fits into a modern graduate or undergraduate program in linguistics, cognitive science, or philosophy. Furthermore, since the technical tools it employs are much simpler to teach and to master, Knowledge of Meaning can be taught by someone who is not primarily a semanticist. Linguistic semantics cannot be studied as a stand-alone subject but only as part of cognitive psychology, the authors assert. It is the study of a particular human cognitive competence governing the meanings of words and phrases. Larson and Segal argue that speakers have unconscious knowledge of the semantic rules of their language, and they present concrete, empirically motivated proposals about a formal theory of this competence based on the work of Alfred Tarski and Donald Davidson. The theory is extended to a wide range of constructions occurring in natural language, including predicates, proper nouns, pronouns and demonstratives, quantifiers, definite descriptions, anaphoric expressions, clausal complements, and adverbs. Knowledge of Meaning gives equal weight to philosophical, empirical, and formal discussions. It addresses not only the empirical issues of linguistic semantics but also its fundamental conceptual questions, including the relation of truth to meaning and the methodology of semantic theorizing. Numerous exercises are included in the book.

A Classification Theory Of Semantics Of Normal Logic Programs: I. Strong Properties

Abstract: Our aim in this article is to present a method for classifying and characterizing the various different semantics of logic programs with negation that have been considered in the last years. Instead of appealing to more or less questionable intuitions, we take a more structural view: our starting point is the observation that all semantics induce in a natural way non-monotonic entailment relations “ |˜ ”. The novel idea of our approach is to ask for the properties of these |˜ -relations and to use them for describing all possible semantics. The main properties discussed in this paper are adaptations of rules that play a fundamental role in general non-monotonic reasoning: Cumulativity and Rationality. They were introduced and investigated by Gabbay, Kraus, Lehmann, Magidor and Makinson. We show that the 3-valued version COMP 3 of Clark's completion, the stratified semantics M supp P as well as the well-founded semantics WFS and two extensions of it behave very regular: they are cumulative, rational and one of them is even supraclassical. While Pereira's recently proposed semantics O-SEM is not rational it is still cumulative. Cumulativity fails for the regular semantics REG-SEM of You/Yuan (recently shown to be equivalent to three other proposals). In a second article we will supplement these strong rules with a set of weak rules and consider the problem of uniquely describing a given semantics by its strong and weak properties together.

The expressive powers of the logic programming semantics

Abstract: We study the expressive of two semantics far deductive databases and logic programming: the well-founded semantics and the stable semantics. We compare them especially to two older semantics, the two-valued and three-valued program completion semantics. We identify the expressive power of the stable semantics and, in fairly general circumstances, that of the well-founded semantics. In particular, over infinite Herbrand universes, the four semantics all have the same expressive power. We discuss a feature of certain logic programming semantics, which we call the Principle of Stratification, a feature allowing a program to be built easily in modules. The three-valued program completion and well-founded semantics satisfy this principle. Over infinite Herbrand models, we consider a notion of translatability between the three-valued program completion and well-founded semantics which is in a sense uniform in the strata. In this sense of uniform translatability we show the well-founded semantics to be more expressive than the three-valued program completion. The proof is a corollary of our result that over non-Herbrand infinite models, the well-founded semantics is more expressive than the three-valued program completion semantics.

An Operational Semantics for Timed CSP

Abstract: An operational semantics is defined for the language of timed CSP, in terms of two relations: an evolution relation, which describes when a process becomes another simply by allowing time to pass; and a timed transition relation, which describes when a process may become another by performing an action at a particular time. It is shown how the timed behaviours used as the basis for the denotational models of the language may be extracted from the operational semantics. Finally, the failures model for timed CSP is shown to be equivalent to may-testing and, thus, to trace congruence.

Semantics of inhibitor nets

Abstract: We discuss an abstract semantics of concurrent systems generalising causal partial orders. The new semantics employs relational structures-called stratified order structures-which comprise causal partial orders and weak causal partial orders. Stratified order structures can be represented by certain equivalence classes of step sequences-comtraces-directly generalising Mazurkiewicz traces. We use Elementary Net Systems with inhibitor arcs as a system model and show that stratified order structures can provide an abstract semantics which is consistent with their operational semantics expressed in terms of step sequences. Two different types of operational rules are considered. We also construct occurrence nets to enable the generation of stratified order structures for a given run of the net.

Formal Syntax and Semantics of Programming Languages: A Laboratory Based Approach

Abstract: From the Publisher: Formal Syntax and Semantics of Programming Languages: A Laboratory Based Approach presents a panorama of techniques in formal syntax, operational semantics and formal semantics. Using a teaching/learning perspective rather than a research-oriented approach, an understanding of the meta-languages is accessible to anyone with a basic grounding in discrete mathematics and programming language concepts. Throughout the book, valuable hands-on laboratory exercises provide the opportunity for practical application of difficult concepts. Various exercises and examples, implementing syntactic and semantic specifications on real systems, give students hands-on practice. Supplemental software is available on disk or via file transfer protocol. This book is suitable for an advanced undergraduate or introductory graduate level course on the formal syntax and semantics of programming languages.

Functional Programming and Input/Output

Abstract: A common attraction to functional programming is the ease with which proofs can be given of program properties. A common disappointment with functional programming is the difficulty of expressing input/output (I/O) while at the same time being able to verify programs. Here, the author shows how a theory of functional programming can be smoothly extended to admit both an operational semantics for functional I/O and verification of programs engaged in I/O. He obtains, for the first time, operational semantics for the three most widely implemented I/O mechanisms for lazy languages, and proves that the three are equivalent in expressive power. He also develops semantics for a form of monadic I/O and verifies a simple programming example. These theories of functional I/O are based on an entirely operational theory of functional programming, developed using Abramsky's "applicative bisimulation." Graduate students and researchers will gain much from reading this book.

Object-based models and languages for concurrent systems : ECOOP '94 Workshop on Models and Languages for Coordination of Parallelism and Distribution, Bologna, Italy, July 5, 1994 : proceedings

Abstract: Rule-based object coordination.- Sender-initiated and receiver-initiated coordination in a global object space.- Correctness-preserving transformations for the design of parallel programs.- Distributed conflicts in communicating systems.- Bauhaus Linda.- On the operational semantics of a coordination language.- Abstracting interactions based on message sets.- Law-governed linda as a coordination model.- Requirements for a composition language.- A model for active object coordination and its use for distributed multimedia applications.- A machine for uncoupled coordination and its concurrent behavior.

Objects and classes, co-algebraically

Abstract: The coalgebraic perspective on objects and classes in object-oriented programming is elaborated: objects consist of a (unique) identifier, a local state, and a collection of methods described as a coalgebra; classes are coalgebraic (behavioural) specifications of objects. The creation of a ``new'''' object of a class is described in terms of the terminal coalgebra satisfying the specification. We present a notion of ``totally specified'''' class, which leads to particularly simple terminal coalgebras. We further describe local and global operational semantics for objects. Associated with the local operational semantics is a notion of bisimulation (for objects belonging to the same class), expressing observational indistinguishability.

The knowledge acquisition and representation language, KARL

Abstract: The Knowledge Acquisition and Representation Language (KARL) combines a description of a knowledge based system at the conceptual level (a so called model of expertise) with a description at a formal and executable level. Thus, KARL allows the precise and unique specification of the functionality of a knowledge based system independent of any implementation details. A KARL model of expertise contains the description of domain knowledge, inference knowledge, and procedural control knowledge. For capturing these different types of knowledge, KARL provides corresponding modeling primitives based on Frame Logic and Dynamic Logic. A declarative semantics for a complete KARL model of expertise is given by a combination of these two types of logic. In addition, an operational definition of this semantics, which relies on a fixpoint approach, is given. This operational semantics defines the basis for the implementation of the KARL interpreter, which includes appropriate algorithms for efficiently executing KARL specifications. This enables the evaluation of KARL specifications by means of testing.

A congruence theorem for structured operational semantics with predicates and negative premises

Abstract: We proposed a syntactic format, the panth format, for structured operational semantics in which besides ordinary transitions also predicates, negated predicates, and negative transitions may occur such that if the rules are stratifiable, strong bisimulation equivalence is a congruence for all the operators that can be defined within the panth format. To show that this format is useful we took some examples from the literature satisfying the panth format but no formats proposed by others. The examples touch upon issues such as priorities, termination, convergence, discrete time, recursion, (infinitary) Hennessy-Milner logic, and universal quantification.

An argumentation-theoretic foundation for logic programming

Abstract: Logic programs are considered as abductive programs with negative literals as abductive hypotheses. A simple framework for semantics of logic programming is introduced based on the notion of acceptable hypotheses. We show that our framework captures, generalizes, and unifies different semantic concepts (e.g., well-founded models, stable models, stationary semantics, etc.) in logic programming. We demonstrate that our framework accommodates in a natural way both the minimalism and maximalism intuitions to semantics of logic programming. Further, we show that Eshghi and Kowalski's procedure is a proof procedure for the abductive semantics. We also give sufficient conditions for the coincidence between different semantics.

The Semantics of Syntax: A Minimalist Approach to Grammar

Abstract: Acknowledgements Pt. I: The Relationship between Form and Meaning 1: The Semantics of Syntax: Defining the Object of Inquiry 2: Selective Semantics and Syntactic Correspondence Pt. II: Selective Semantics and the Lexicon 3: A Case Study of Six French Verbs Pt. III: Selective Semantics and Syntax 4: Psych Verbs 5: Verb Movement Afterword Notes References

Formal Semantics for VHDL

Abstract: From the Publisher: It is recognized that formal design and verification methods are an important requirement for the attainment of high quality system designs. The field has evolved enormously during the last few years, resulting in the fact that formal design and verification methods are nowadays supported by several commercially- and academically-based tools. Having different tools and users generating and reading the same language requires that the same semantics is assigned by them to all constructs and elements of the language. The current IEEE standard VHDL language reference manual (LRM) tries to define VHDL as well as possible in a descriptive way, explaining the semantics in English. But rigor and clarity is very hard to maintain in a semantics defined in this way, and that has already given rise to many misconceptions and contradictory interpretations. Formal Semantics for VHDL is the first book that puts forward a cohesive set of semantics for the VHDL language. The chapters describe several semantics each based on a different underlying formalism: two of them use Petri nets as target language, and two of them higher order logic. Two use functional concepts, and finally another uses the concept of evolving algebras. Formal Semantics for VHDL is essential reading for researchers in Formal Methods and can be used as a text for an advanced course on the subject.

The semantics of future and its use in program optimization

Abstract: The future annotations of MultiLisp provide a simple method for taming the implicit parallelism of functional programs. Past research concerning futures has focused on implementation issues. In this paper, we present a series of operational semantics for an idealized functional language with futures with varying degrees of intensionality. We develop a set-based analysis algorithm from the most intensional semantics, and use that algorithm to perform touch optimization on programs. Experiments with the Gambit compiler indicates that this optimization substantially reduces program execution times.

A Delegation-based Object Calculus with Subtying

Abstract: This paper presents an untyped object calculus that reflects the capabilities of so-called delegation-based object-oriented languages. A type inference system allows static detection of errors, such as message not understood, while at the same time allowing the type of an inherited method to be specialized to the type of the inheriting object. The main advance over previous work is the provision for subtyping in the presence of delegation primatives. This is achieved by distinguishing a prototype, whose methods may be extended or replaced, from an object, which only responds to messages for which it already has methods. An advantage of this approach is that we have full subtyping without restricting the “runtime” use of inheritance. Type soundness is proved using operational semantics and an analysis of typing derivations.

On the equivalence of semantics for normal logic programs

Abstract: Despite the frequent comment that there is no general agreement on the semantics of logic programs, this paper shows that a number of independently proposed extensions to the stable model semantics coincide: the regular model semantics proposed by You and Yuan, the partial stable model semantics by Sacca and Zaniolo, the preferential semantics by Dung, and a stronger version of the stable class semantics by Baral and Subrahmanian. We show that these equivalent semantics can be characterized simply as selecting a particular kind of stable classes, called normal alternating fixpoints . In addition, we indicate that almost all of the previously proposed semantic frameworks coincide with that of normal alternating fixpoints. Due to its simplicity and naturalness, the framework of normal alternating fixpoints offers great potential in the study of the semantics for various nonmonotonic systems.

Time and space profiling for non-strict, higher-order functional languages

Abstract: We present the first profiler for a compiled, non-strict, higher-order, purely functional language capable of measuring time as well as space usage. Our profiler is implemented in a production-quality optimising compiler for Haskell, has low overheads, and can successfully profile large applications.A unique feature of our approach is that we give a formal specification of the attribution of execution costs to cost centres. This specification enables us to discuss our design decisions in a precise framework. Since it is not obvious how to map this specification onto a particular implementation, we also present an implementation-oriented operational semantics, and prove it equivalent to the specification.

A fully abstract semantics of classes for Object-Z

Abstract: This paper presents a fully abstract semantics of classes for the object oriented formal specification language Object-Z. Such a semantics includes no unnecessary syntactic details and, hence, describes a class in terms of the external behaviour of its objects only. The semantics, based on an extension of existing process models, defines a notion of behavioural equivalence which is stronger than that of CSP and weaker than that of CCS.

A Stack-Based Approach to Query Languages

Abstract: Scoping, naming and binding are central concepts in the definition and understanding of programming languages. With the introduction of sophisticated data models, these issues become important for query languages as well. Additionally, the goal of integrating query and programming languages requires a common basis for their operational semantics. We offer here an approach to the definition of the operational semantics of query languages based on an abstract machine, in which names, their bindings, and scopes defined by query and data structure are central. The machine has own simple data model for its store, and has a stack for dealing with scopes. We argue for the generality of the approach and illustrate it by defining the semantics of many query language primitives. Finally, we briefly consider how assignment and procedures can be neatly added.

A theory of higher order communicating systems

Abstract: A calculus of higher order communicating systems (CHOCS) was presented by the author in ["Proceedings of POPL 89," pp. 143-154, Assoc. Computing Machinery, New York]. This calculus considers sending and receiving processes to be as fundamental as nondeterminism and parallel composition. In this paper we present an investigation of the foundation of the theory of this calculus, together with the full proofs of all major theorems. CHOCS is an extension of Milner′s Calculus of Communicating Systems (CCS) in the sense that all the constructions of CCS are included or may be derived from more fundamental constructs. Most of the mathematical framework of CCS carries over almost unchanged. The operational semantics of CHOCS is given as a labelled transition system and it is a direct extension of the semantics of CCS with value passing. A set of algebraic laws satisfied by the calculus is presented. These are similar to the CCS laws, varying only by introducing obvious extra laws for sending and receiving processes. The power of process passing is underlined by a result showing that recursion can be simulated by means of process passing and communication.

Nondeterministic Extensions of Untyped λ-Calculus

Abstract: The main concern of this paper is the interplay between functionality and nondeterminism. We ask whether the analysis of parallelism in terms of sequentiality and nondeterminism, which is usual in the algebraic treatment of concurrency, remains correct in the presence of functional application and abstraction, We argue in favour of a distinction between nondeterminism and parallelism, due to the conjunctive nature of the former in contrast to the disjunctive character of the latter. This is the basis of our analysis of the operational and denotational semantics of the nondeterministic ?-calculus, which is the classical calculus plus a choice operator, and of our election of bounded indeterminacy as the semantic counterpart of conjunctive nondeterminism. This leads to operational semantics based on the idea of must preorder, coming from the classical theory of solvability and from the theory of process algebras. To characterize this relation, we build a model using the inverse limit construction over nondeterministic algebras, and we prove it fully abstract using a generalization of Bohm trees. We further prove conservativity theorems for the equational theory of the model and for other theories related to nondeterministic ?-calculus with respect to classical ?-theories.

Active Database Rules with Transaction-Conscious Stable-Model Semantics

Abstract: Semantics represents a major problem area for active databases in as much as (i) there is no formal framework for defining an implementation-independent semantics of active rules, and (ii) the various systems developed so far have ad-hoc operational semantics that are widely different from each other. This situation contributes to the difficulty of predicting the run-time behavior of sets of rules: thus, ensuring the termination of a given set of rules is currently viewed as a major research issue. In this paper, we introduce a durable change semantics for active database rules; this semantics improves Starburst's deferred activation notion with concepts taken from Postgres and Heraclitus and the semantic foundations of deductive databases. We provide a formal logic-based model for this transaction-oriented semantics, show that it is amenable to efficient implementation, and prove that it solves the non-termination problem.

CoLan: a functional constraint language and its implementation

Abstract: This paper is about the definition of CoLan, a high-level declarative Constraint Description Language, for use with an Object-Oriented Database (OODB). CoLan has features of both first-order logic and functional programming and is based on Daplex. CoLan expressions are translated into Prolog code that implements the operational semantics of the constraint. Pieces of generated code are cached inside the class descriptor of the ‘host’ class attached to appropriate slots. The pieces of code are retrieved along an inheritance path when an update on the database is attempted. If the update violates any of the retrieved constraints then it is rejected with an informative message. Thus constraints are expressed declaratively and they can even be retracted individually. However, they are implemented efficiently as code-generated methods, triggered selectively by an update. The implementation is described for the ADAM OODB, which uses meta-classes of the CoLan system to generate class descriptions.

Proof theoretic approach to specification languages

Abstract: In this thesis I study FORUM as a specification language. FORUM is a higher-order logic based on the logical connectives of Linear Logic. As an initial example, I demonstrate that FORUM is well suited for specifying concurrent computations by specifying the higher-order $\pi$ calculus. Next, I focus on the problem of specifying programming languages with higher-order functions, and imperative features such as assignable variables, exceptions and first-class continuations. I provide a modular and declarative specification of an untyped programming language, UML, which contains the above mentioned features. Further, I use the proof theory of FORUM to study program equivalence for the functional core of UML augmented with assignable variables. Using my compositional specifications in FORUM, I prove equivalence of programs that have been challenging for other specification languages. Finally I study the operation semantics of DLX, a prototypical RISC machine. I specify the sequential and pipelined operational semantics of DLX with important optimizations such as call-forwarding and early branch resolution, and prove them to be equivalent. Furthermore, I study the problem of code equivalence via the FORUM specification, and, in particular, analyze the problem of code rescheduling for DLX.

CCS with priority choice

Abstract: This paper investigates an extension of Milner′s CCS with a priority choice operator called prisum: this operator is very similar to the PRIALT construct of Occam. The new binary prisum operator only allows execution of its second component in the case where the environment is not ready to allow the first component to proceed. This dependency on the set of actions the environment is ready to perform goes beyond that encountered in traditional CCS. Its expression leads to a novel operational semantics in which transitions carry ready-sets (of the environment) as well as the normal action symbols from CCS. A notion of strong bisimulation is defined on agents with priority via this semantics. It is a congruence and satisfies new equational laws (including a new expansion law) which are shown to be complete for finite agents with prisum. The laws are conservative over agents of traditional CCS.

On the declarative and procedural semantics of deductive object-oriented systems

Abstract: We present declarative and procedural semantics for a deductive object-oriented language, Gulog. The declarative semantics is based on preferred minimal models. We describe both bottom-up and top-down query evaluation procedures and show that they are sound with respect to the declarative semantics. The results contribute to our understanding of the interaction of inheritance, overriding and deduction in the presence of both functional and set-valued methods, and multiple inheritance.