Several scientific bottlenecks have been identified in existing component-based approaches. Among them, we focus on the identification of a relevant abstraction for the component expression and verification of properties like substitutivity: When is it possible to formally accept or reject the substitution of a component in a composition? This paper suggests max/plus automata to tackle this problem when considering a new factor – Quality of Service (QoS). Four notions of simulation-based substitutivity managing QoS aspects are proposed, and related complexity issues on max/plus automata are investigated.

Web services (WSs) are used more and more as components of distributed applications with a goal to resolve complex tasks that simple services cannot. This use of WSs is connected to the emergence of languages like WS-BPEL which allows describing the external behaviour of WSs on top of the service interfaces. The use of WSs as components of distributed applications implies the possibility to change a failing service for another which can do at least the same thinks as the replaced service. Different solutions have been proposed during the last years to check such properties, but, to our knowledge, none of them take QoS aspects into account. This paper introduces a set of tools and techniques for verifying WSs substitutivity while taking into account service costs such as the execution time of the different operations provided by WSs.

Web services (WSs) are used more and more as components of distributed applications with a goal to resolve complex tasks that simple services cannot. This use of WSs is connected to the emergence of languages like WS-BPEL which allows describing the external behaviour of WSs on top of the service interfaces. The use of WSs as components of distributed applications implies the possibility to change a failing service for another which can do at least the same things as the replaced service. The composition issues are also of particular interest to WSs users. Different solutions have been proposed during the last years to check such properties, but, to our knowledge, none of them takes QoS aspects into account. This paper introduces underpinnings and a tool for verifying WSs substitutivity and well-formed composition while considering WSs costs such as the execution time of the different operations provided by WSs.