Christine Choppy

Abstract data types with exception handling: an initial approach based on a distinction between exceptions and errors

Abstract In this paper, a new semantics for exception handling in algebraic specifications is provided. Our formalism allows all forms of exception and error handling (several error messages, implict error propagation rule, exception recovery policy), while preserving the existence of initial models. The main concepts of our approach are: the distinction between exception and error, and the introduction of exception labelling allowing to formalize various error messages. This formalism allows use of congruences in a similar manner as in the classical abstract data type theory. Moreover, we show how a functional semantics of enrichment can be carried over to our framework, and we show how hierarchical consistency and sufficient completeness can be redefined. Then, we briefly sketch out how abstract implementations can be extended in order to include exception handling. Indeed, abstract implementation of specifications including exception handling was one of main motivations for the work reported here.

The ASSPEGIQUE Specification Environment - Motivations and Design

In this paper we describe ASSPEGIQUE, an integrated environment for the development of large algebraic specifications and the management of a specification data base. We focus on what motivated us when designing this environment, some crucial design choices and the specific CIGALE parser tool which is extensively used in ASSPEGIQUE.

Abstract implementations and correctness proofs

In this paper, we present a new semantics for the implementation of abstract data types. This semantics leads to a simple, exhaustive description of the abstract implementation correctness criteria. These correctness criteria are expressed in terms of sufficient completeness and hierarchical consistency. Thus, correctness proofs of abstract implementations can always be handled using classical tools such as theorem proving methods, structural induction methods or syntactical methods (e.g. fair presentations). The main idea of our approach is the use of intermediate “concrete sorts”, which synthesize the available values used by implementation. Moreover, we show that the composition of several correct abstract implementations is always correct. This provides a formal foundation for a methodology of program development by stepwise refinement.

About the “correctness” and “adequacy” of PLUSS specifications

In the context of algebraic specifications written in Pluss, this paper investigates various issues raised by the question: “Is my specification correct?”. Up to now the only ways to check the adequacy of a specification with respect to the problem to be solved are through running a prototype on appropriate examples, or through the use of the specification to prove consequent (expected) properties. Before this problem may be fully addressed, issues regarding the specification consistency and the correctness of the prototype w.r.t. the specification must be studied. In this paper, various issues concerning checking consistency and proving properties of PLUSS specifications are presented. It is investigated how general properties can be proved using an appropriate presentation of the specification that may be understood by a prototyping tool. While this study is done in the framework of the pluss specification language, it should be clear that most of the issues considered here arise in a similar way with other specification languages.

Algorithmic Complexity of Term Rewriting Systems

For the class of the regular term rewriting systems, we have provided ways of obtaining asymptotic evaluations of the cost series. The user does not need to actually manipulate formal series, since our results are given under the form of ready-to-use formulae. These results solely depend on physical characteristics of the system, easily obtainable : number of variables and of constructors in the lefthand sides, occurrences of derived operators in the right-hand sides. Then, the average cost is constant, polynomial or exponential, according to the position of the singularity of the expressions Qi(N(z)) closest to the origin.

Recent Trends in Data Type Specification

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Integrating ASSPEGIQUE and LP

In this paper, we present various issues w.r.t. proving properties of PLUSS specifications with LP, and building an integrated interface between ASSPEGIQUE (the environment that supports PLUSS) and LP. We investigate how general properties can be proved using an adequate presentation of the specification that may be understood by LP. We address the issue of interfacing the two environments in a way that would be as “transparent” to the user as possible.

Algebraic Semantics of Exception Handling

In this paper, a new semantics for exception handling in algebraic specifications is provided. Our formalism allows all forms of exception and error handling (several error messages, implicit error progagation rule, exception recovery policy), while preserving the existence of initial models. It handles complex examples where various exceptional cases (leading to different processings) can be specified. The main concept of our approach is the distinction between exception and error. This formalism allows use of congruences in a similar manner as in the classical abstract data type theory. Moreover, we show how a functorial semantics of enrichment can be carried over to our framework, and we show how hierarchical consistency and sufficient completeness can be redefined. These results provide a firm basis for writing modular, structured specifications with exception handling features.

The design and specification of the ASSPEGIQUE database

Among the design issues for symbolic computation systems, a non trivial one is the design of the database where informations (specifications, proofs, test sets, program modules, etc.) that are necessary to use the various tools available are stored. In this paper we address the design of a database for an algebraic specification environment, and provide an algebraic specification for this database management. One of the issues in this design is to distinguish between “static” aspects, i.e. the attribute updating that is necessary to preserve the database consistency when a single action takes place, and the “dynamic” aspects, that take into account the management of concurrent accesses to the database. The specification language modularity was crucial in order to correctly specify such notions as “coherent list of attributes”, “coherent list of modules”, etc. Since various cases of attribute dependencies were studied (transitive dependence of a given module attributes, and dependence w.r.t. other module attributes), the specification may be easily modified to take into account modifications in the environment architecture (when new tools are added, some new attributes may be necessary). In the same way, this specification could be adapted to specify other symbolic computation systems database management.