The Computer Journal Advance Access originally published online on July 31, 2007
The Computer Journal 2007 50(5):522-534; doi:10.1093/comjnl/bxm014
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Service Availability in Concurrent Systems—Part I: A Theory of Hierarchical Services of Interacting Processes
1 Department of IT and Computer Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran
2 Department of Electrical and Computer Engineering, Tarbiat Modares University, Tehran, Iran
* Corresponding author: sharafat{at}isc.iranet.net
Received 27 May 2006; revised 28 December 2006
A novel formal model is introduced that is tailored to the treatment of the service availability problem in concurrent systems. This model, called hierarchical services of interacting processes (HSIP), incorporates the hierarchy of services, processes, shared variables, and dense time to reason about services quantitatively. The underlying concept is that a service, via its hierarchy, relates to a number of so-called ‘atomic services’ at the bottom of the hierarchy that are the outcomes of actions having no subaction within. The services in a hierarchy are the results 
of processes acting and interacting with each other to provide the service at the top of the hierarchy. These processes can completely be described by actions resulting in atomic services. The main features of HSIP are twofold. First, through this model, a wide range of quasi-isolated problems such as mutual exclusion, system reconfiguration, fault tolerance, resource allocation, denial of service, and quality of service can be stated and analyzed in a cohesive manner. Second, it retains the use of shared variables, but resolves the main shortcoming of the shared-variable approach, which is the implicitness of interactions among system components.
Key Words: axiomatic method • concurrent systems • requirement specification • service availability