Quality of Service Contracts
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(1) speaks also about Quality of Service Contracts. In my understanding these questions need to be answered: Is the service synchronous or asynchronous. If it is asynchronous, are there queues (serialization contexts) or not? If there are queues, which type of queues like exactly once in order (EOIO) or Exactly Latest (EL). Also the question is relevant which granularity do the queues have.
Why is this relevant? Why can this not merely be ignored as a technical detail of the implementation?
It can not be ignored at the time of design of a contract, because it determines the possible situations (states of the process) that may occur and that need to be resolved in the design of the contract which implies the ability to design choreographies.
To make an example. If it is only possible to update a sales order synchronously, then the contract needs not to be designed in a way to deal with a concurrent asynchronous cancellation of a previous sales confirmation, that might have happened in an asynchronous update scenario. And the resolution is not merely a technical resolution, but the resolution is better done on the business level – as for example discussed in (2). Therefore the QoS Contract implies needed resolutions on the business level – that need to be designed into the behavioral contract and into the syntactical contract.
Bibliography
1. Beugnard, Antoine, et al. Making Components Contract Aware. Computer. 1999, Vol. 32, 7, pp. 38 – 45. http://portal.acm.org/citation.cfm?id=621275.
2. Lecture Notes in Computer Science: Non-desynchronizable Service Choreographies. Decker, Gero and Alistair Barros, Frank Michael Kraft and Niels Lohmann. Berlin / Heidelberg : Springer, 2008. Service-Oriented Computing – ICSOC 2008. Vol. 5364/2008, pp. 331-346. http://www.springerlink.com/content/9055736715131767/. ISSN 0302-9743 (Print) 1611-3349 (Online).
