Dependability Assessment of Services

N. Looker “Dependability Assessment of Services ,” presented at Seventh SOSoRNet Workshop on Dependable, Dynamic Distributed Services and Systems, 6th November 2007, Woodhouse Rooms, University House, University of Leeds.

Abstract: Web Services are a heavily used middleware in eCommerce and also make a major contribution to Grid computing. Given the prominence of this technology it is vital that methods are developed to ensure that dependable services and middleware products are deployed.

Dependability is a discipline that provides an assessment of how much trust can be placed on a service to deliver its specified function. Systems need not be fault free but should deliver their required functionality when required. This is because it is virtually impossible to engineer a system that can be guaranteed to be fault free; so dependability assumes that faults exist in a system but mechanisms exist to either eliminate them or tolerate their presence. In either case a dependable system will perform its intended function.

Validation and verification techniques attempt to determine that a system contains no faults, which is an important discipline and increases the overall reliability of a system, but is difficult to achieve with current techniques. Dependability is a more realistic approach since it measures the reliance that can be placed upon a system rather than validating it against its specification and includes methods that increase this.