Jjm Jozef Hooman

Verification and improvement of the sliding window protocol

The well-known Sliding Window protocol caters for the reliable and efficient transmission of data over unreliable channels that can lose, reorder and duplicate messages. Despite the practical importance of the protocol and its high potential for errors, it has never been formally verified for the general setting. We try to fill this gap by giving a fully formal specification and verification of an improved version of the protocol. The protocol is specified by a timed state machine in the language of the verification system PVS. This allows a mechanical check of the proof by the interactive proof checker of PVS. Our modelling is very general and includes such important features of the protocol as sending and receiving windows of arbitrary size, bounded sequence numbers and channels that may lose, reorder and duplicate messages.

Process Algebra in PVS

The aim of this work is to investigate mechanical support for process algebra, both for concrete applications and theoretical properties. Two approaches are presented using the verification system PVS. One approach declares process terms as an uninterpreted type and specifies equality on terms by axioms. This is convenient for concrete applications where the rewrite mechanisms of PVS can be exploited. For the verification of theoretical results, often induction principles are needed. They are provided by the second approach where process terms are defined as an abstract datatype with a separate equivalence relation.

Incorporating Formal Techniques into Industrial Practice: an Experience Report

We report about experiences at Philips Healthcare with component-based development supported by formal techniques. The formal Analytical Software Design (ASD) approach of the company Verum has been incorporated into the industrial workflow. The commercial tool ASD:Suite supports both compositional verification and code generation for control components. For other components test-driven development has been used. We discuss the results of these combined techniques in a project which developed the power control service of an interventional X-ray system.

Evaluating the effect of a lightweight formal technique in industry

We evaluate the effect of applying the commercial formal technique Analytical Software Design (ASD) to an industrial project. In ASD, interfaces and software designs are modelled using a formal tabular notation. The ASD tool set supports formal checks of these models, such as deadlock freedom and interface compliance. In addition, full code can be generated from design models. ASD has been applied at Philips Healthcare to develop parts of the software of interventional X-ray systems. We report about the experiences with the embedding of ASD into the development processes. The quality of the resulting code and the productivity has been analysed and compared to code developed with other techniques. We observe that the use of ASD leads to a strong reduction of the number of defects and an increase in productivity. The results are also compared to the literature about standards and related projects at other companies.

Semantic models of a timed distributed dataspace architecture

We investigate various formal aspects of a distributed dataspace architecture in which data storage is based on time stamps. An operational and a denotational semantics have been defined and the equivalence of these two formulations has been proved. Moreover, the denotational semantics is fully abstract with respect to the observation of produced data items. It is used as a basis for compositional reasoning about components, supported by the interactive theorem prover PVS. We use this framework for a small example where components make mutual assumptions about each others output.

Serializability Preserving Extensions of Concurrency Control Protocols

The verification system PVS is used to obtain mechanized support for the formal specification and verification of concurrency control protocols, concentrating on database applications. A method to verify conflict serializability has been formulated in PVS and proved to be sound and complete with the interactive proof checker of this tool. The method has been used to verify a few basic protocols. Next we present a systematic way to extend these protocols with new actions and control information. We show that if such an extension satisfies a few simple correctness conditions, the new protocol is serializable by construction.