Joseph C. Okika

Modelling with Relational Calculus of Object and Component Systems - rCOS

This chapter presents a formalization of functional and behavioural requirements, and a refinement of requirements to a design for CoCoME using the Relational Calculus of Object and Component Systems(rCOS). We give a model of requirements based on an abstraction of the use cases described in Chapter 3.2. Then the refinement calculus of rCOS is used to derive design models corresponding to the top level designs of Chapter 3.4. We demonstrate how rCOS supports modelling different views and their relationships of the system and the separation of concerns in the development.

Classification of SOA Contract Specification Languages

There are numerous existing notations and standards in the Web service community. These may be grouped broadly into three competing families, namely; Web services, semantic Web, and electronic business. Although the families are competing, we expect that applications will cut across them and there is a need to map from one to another and to analyze compatibility and other properties. Therefore we survey how they deal with different aspects. We then illustrate with examples, the aspects of contracts captured by one language from each of the three competing families in addition to WSDL, the core standard for Web services description. The result is a classification based on the aspects of computations: functionality, protocol, and for instance performance covered by the languages. The classification is used to identify similarities between semantic models and thus find potential mappings between the families. Furthermore, this gives a handle on analysis techniques that may apply to the aspects in a particular family.

On the Specification of Full Contracts

Contracts specify properties of an interface to a software component. We consider the problem of defining a full contract that specifies not only the normal behaviour, but also special cases and tolerated exceptions. In this paper we focus on the behavioural properties of use cases taken from the Common Component Modelling Example (CoCoME), proposed as a benchmark to compare different component models. We first give the full specification of the use cases in the deontic-based specification language CL, and then we concentrate on three particular properties in order to compare deontic and operational specifications. We conjecture that operational specifications are well suited for normal cases, but are less easily extended for exceptional cases. This hypothesis is investigated by comparing specifications in CSP (operational) with specifications in CL. The outcome of the experiment supports the conjecture and demonstrates clear differences in the basic descriptive power of the formalisms.

Analyzing Web Service Contracts

Web services should be dependable, because businesses rely on them. For that purpose the service oriented architecture has standardized specifications at a syntactical level. In this paper, we demonstrate how such specifications are used to derive semantic models in the form of (timed) automata. These can be used to model check functional and behavioural properties of a given service. Since there might be several specifications dealing with different aspects, one must also check that these automata are consistent, where we propose to set up a suitable simulation relation. The proposed techniques are illustrated with a small case study.