Lamia Labed Jilani

Defining and applying measures of distance between specifications

Echoing Louis Pasteurs quote, we submit the premise that it is advantageous to define measures of distance between requirements specifications because such measures open up a wide range of possibilities both in theory and in practice. The authors present a mathematical basis for measuring distances between specifications and show how their measures of distance can be used to address concrete problems that arise in the practice of software engineering.

Retrieving software components that minimize adaptation effort

Given a software library whose entries are represented by formal specifications, we distinguish between two retrieval procedures: exact retrieval, whereby, given a query K, we identify all the library components that are correct with respect to K; approximate retrieval, which is invoked when exact retrieval fails, and identifies the library components that minimize adaptation effort. To this effect, we define four measures of functional distance between specifications, and discuss algorithms that minimize these measures over a set of components; then we discuss whether these measures can be used to predict adaptation effort.

Invariant assertions, invariant relations, and invariant functions

Abstract Invariant assertions play an important role in the analysis and documentation of while loops of imperative programs. Invariant functions and invariant relations are alternative analysis tools that are distinct from invariant assertions but are related to them. In this paper we discuss these three concepts and analyze their relationships. The study of invariant functions and invariant relations is interesting not only because it provides alternative means to analyze loops, but also because it gives us insights into the structure of invariant assertions, hence it may help us enhance techniques for generating invariant assertions.

Computing preconditions and postconditions of while loops

Weakest preconditions were introduced by Dijkstra as a tool to define the semantics of programming constructs, and thereby as a means to prove the correctness of programs; the dual concept of strongest postcondition was introduced subsequently as an alternative means for the same ends. In this paper, we present and discuss a method to compute weakest preconditions and strongest postconditions of while loops in a C-like programming language; to this effect, we use the concept of invariant relation. Whereas the task of computing weakest preconditions and strongest postconditions of while loops is usually approached by limiting the number of iterations and applying successive sequential compositions, invariant relations afford us a crisper, closed form solution.

A versatile concept for the analysis of loops

Abstract Ever since their introduction by Hoare in 1969, invariant assertions have, justifiably, played a key role in the analysis of while loops. In this paper, we discuss a distinct but related concept, viz invariant relations, and show how these can be used to answer many questions pertaining to the analysis of loops, including: how to compute the function of the loop; how to compute an invariant assertion of the loop; how to compute a weakest precondition of the loop; how to compute a strongest postcondition of the loop; how to compute the termination condition of a loop; how to verify whether the loop computes a given function; how to verify whether the loop is correct with respect to a given specification; and finally how to compute an invariant function for the loop. Using a tool we have developed at the University of Tunis to derive invariant relations, we show how all these tasks can be automated by means of a computer algebra system, viz Mathematica (©Wolfram Research). Whenever applicable, we compare the performance of our tool against the performance of others.

Verifying while loops with invariant relations

Traditionally, invariant assertions are used to verify the partial correctness of while loops with respect to pre/post specifications. In this paper we discuss a related but distinct concept, namely invariant relations, and show how invariant relations are a more potent tool in the analysis of while loops: whereas invariant assertions can only be used to prove partial correctness, invariant relations can be used to prove total correctness; also, whereas invariant assertions can only be used to prove correctness, invariant relations can be used to prove correctness and can also be used to prove incorrectness; finally, where traditional studies of loop termination equate termination with iterating a finite number of times, we broaden the definition of termination to also capture the condition that each individual iteration proceeds without raising an exception.

Invariant functions and invariant relations: An alternative to invariant assertions

Whereas the analysis of loops in imperative programs is, justifiably, dominated by the concept of invariant assertion, we submit a related but different concept, of invariant relation, and show how it can be used to analyze diverse aspects of a while loop. We also introduce the concept of invariant function, which is used to generate a broad class of invariant relations.

A Study of E-Government Architectures

The success of an e-government initiative depends on different factors such as economic strategies, countries political and decisions initiatives, countries readiness to citizen connectivity, etc. We concentrate in this paper on architectural design of e-government systems according to a software engineering point of view which among all other considerations promises also the success of the final operational platform. In fact, architectural design is a key factor for a success of any system. The purpose of this paper is to study and analyze existing (software) architectures of e-government systems in order to have a better vision of the architecture underlying and characterizing an EGP (E-Government Platform). This is fundamental before proposing our own architecture, particularly for a federated project of research S2EG, conducted in the context of Tunisia country e-government initiative. In this presented work, we particularly want to highlight architectural design principles, the high level components that constitute the architecture, specifically the software components and the used technology.

Modeling security as a dependability attribute: a refinement-based approach

As distributed, networked computing systems become the dominant computing platform in a growing range of applications, they increase opportunities for security violations by opening hitherto unknown vulnerabilities. Also, as systems take on more critical functions, they increase the stakes of security by acting as custodians of assets that have great economic or social value. Finally, as perpetrators grow increasingly sophisticated, they increase the threats on system security. Combined, these premises place system security at the forefront of engineering concerns. In this paper, we introduce and discuss a refinement-based model for one dimension of system security, namely survivability.

Invariant relations, invariant functions, and loop functions

The increasing criticality of software applications, the increasing size and complexity of such applications, and the increasing reliance of software engineering paradigms on third party software assets combine to place a high premium on the ability to analyze software products to an arbitrary level of thoroughness and precision. Yet despite several decades of research, the goal of analyzing the functional properties of software products to an arbitrary level of thoroughness and precision remains unfulfilled. In this paper, we discuss the use of a relation-theoretic approach inspired from Mills’ logic to analyze while loops, and we support our approach by an operational prototype tool. The proposed method and tool have applications in program comprehension, reverse engineering, program verification, software maintenance, and programmer education.