Service Verification Research Articles

A snapshot of public web services

Web Service Technology has been developing rapidly as it provides a flexible application-to-application interaction mechanism. Several ongoing research efforts focus on various aspects of web service technology, including the modeling, specification, discovery, composition and verification of web services. The approaches advocated are often conflicting---based as they are on differing expectations on the current status of web services as well as differing models of their future evolution. One way of deciding the relative relevance of the various research directions is to look at their applicability to the currently available web services. To this end, we took a snapshot of the currently publicly available web services. Our aim is to get an idea of the number, type, complexity and composability of these web services and see if this analysis provides useful information about the near-term fruitful research directions.

Discussion summary

This is a summary of the comments from a discussion session at the end of the Workshop on Testing, Analysis and Verification of Web Services (TAV-WEB) 2004. The comments were made by the workshop participants, and were compiled and edited by the workshop organizers.TAV-WEB 2004 was held in conjunction with ISSTA 2004 in Boston, Massachusetts on July 11, 2004. The abstracts of the papers presented in TAV-WEB 2004 appear in the September issue of SEN.

Requirements-Driven Verification of Web Services

We propose a requirements-driven approach to the design and verification of Web services. The proposed methodology starts from a requirements model, which defines a business domain at a “strategic” level, describing the participating actors, their mutual dependencies, goals, require- ments, and expectations. This business requirements model is then refined into a business process model. In this refinement, definitions of the processes carried out by the actors of the domain are added to the model in the form of BPEL4WS code. We show how to exploit model checking tech- niques for the verification of the specification, both at the requirements and at the process level. At the requirements level, model checking is used to validate the specification against a set of queries specified by the designer; at the process level, it is used to verify if the BPEL4WS processes satisfy the constraints described in the requirements model.

Conversation protocols: a formalism for specification and verification of reactive electronic services

This paper focuses on the realizability problem of a framework for modeling and specifying the global behaviors of reactive electronic services (e-services). In this framework, Web accessible programs ( peers) communicate by asynchronous message passing, and a virtual global watcher silently listens to the network. The global behavior is characterized by a “conversation”, which is the infinite sequence of messages observed by the watcher. We show that given a Büchi automaton specifying the desired set of conversations, called a “conversation protocol”, it is possible to realize the protocol using a set of finite state peers if three realizability conditions are satisfied. In particular, the synthesized peers will conform to the protocol by generating only those conversations specified by the protocol. Our results enable a top-down verification strategy where (1) A conversation protocol is specified by a realizable Büchi automaton, (2) The properties of the protocol are verified on the Büchi automaton specification, and (3) The peer implementations are synthesized from the protocol via projection.

Formal verification of dependable distributed protocols

Dependable distributed systems often employ a hierarchy of protocols to provide timely and reliable services. Such protocols have both dependability and real-time attributes, and the verification of such composite services is a problem of growing complexity even when using formal approaches. Our intention in this paper is to exploit the modular design aspects appearing in most dependable distributed protocols to provide formal level of assurance for their correctness. We highlight the capability of our approach through a case study in formal modular specification and tool-assisted verification of a timestamp-based checkpointing protocol. Furthermore, during the process of verification, insights gained in such a stack of protocols have assisted in validating some additional properties those dealing with failure recovery.

Network integration testing: concepts, test specifications and tools for automatic telecommunication services verification

The purpose of this tutorial is to provide concepts and historical background of the “network integration testing” (NIT) methodology. NIT is a “grey box” testing technique that is aimed at verifying the correct behaviour of interconnected networks (operated by different operators) in provisioning services to end users, or the behaviour of a complex network operated by a unique operator. The main technical concepts behind this technique are presented along with the history of some International projects that have contributed to its early definition and application. European Institute for Research and Strategic Studies in Telecommunication (EURESCOM) has actually been very active, with many projects, in defining the NIT basic methodology and providing actual NIT specifications (for narrow-band and broad-band services, covering both voice and data). EURESCOM has also been acting as a focal point in the area, e.g., encouraging the Industry in developing commercial tools supporting NIT. In particular, the EURESCOM P412 project (1994–1996) first explicitly defined the NIT methodology (the methodological aspects include test notation, test implementation, test processes, distributed testing and related co-ordination aspects). P412 applied the methodology to ISDN whilst another project, P410, applied NIT to data services. The P613 project (1997–1999) extended the basic NIT methodology to the broad band and GSM. More into details, the areas covered currently by NIT test specifications developed by EURESCOM projects include N-ISDN, N-ISUP, POTS, B-ISDN, B-ISUP, IP over ATM, ATM/FR, GSM, focusing also on their “inter-working” cases (e.g., ISDN/ISDN, ISDN/GSM, etc.). ETSI, the European Telecommunication Standards Institute, also contributed to NIT development (e.g., the definition of the TSP1+ protocol, used for the functional co-ordination and timing synchronisation of all tools involved in a distributed testing session). The paper also discusses NIT in relation to the recent major changes (processes) within the telecommunication (TLC) community. Beyond the new needs coming from the pure technical aspects (integration of voice and data, fixed mobile convergence, etc.) the full deregulation of the TLC sector has already generated new processes and new testing needs (e.g., Interconnection Testing) that had a significant influence on the methodology. NIT is likely to continue to develop further in the future according to the needs of telecom operators, authorities, user’s associations and suppliers.

Manipulator system for constructing overhead distribution lines

Two manipulator systems differing in operating method were developed. Their serviceability verification using real-scale model distribution lines revealed that both systems can perform a series of work elements of test operation, offering the prospect that the remote operation system can be introduced in distribution line construction work. The on-boom operation system needs TV cameras to be arranged to obtain the necessary visual information from behind the work place. However, it enables the operator to make direct visual inspection of the work and offers the ease of having depth perception and shifting the observing point.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Manipulator System for Constructing Overhead Distribution Lines

Two manipulator systems differing in operating method were developed. Their serviceability verification using real-scale model distribution lines revealed that both systems can perform a series of work elements of test operation, offering the prospect that the remote operation system can be introduced in distribution line construction work. The on-boom operation system needs TV cameras to be arranged to obtain the necessary visual information from behind the work place. However, it enables the operator to make direct visual inspection of the work and offers the ease of having depth perception and shifting the observing point. >

Pricing Health Services Verification of a Monopoly Pricing Model for Dentistry

A model of monopoly with constant marginal costs is used to derive a price function for dental services. The implications of the model are tested using data on individual practitioners from a national survey. The implications of the model are met by the data, providing strong evidence of the appropriateness of the monopoly model to analyses of the market for dental services. The empirical evidence also provides substantial information on the determinants of dental fees.