A compensation mechanism in GIS web service composition

With the evolution of GIS front stand-alone systems with geo-data tightly coupled with systems to an increasingly distributed model based on independently-provided, interoperable GIS Web Service, much more research has been focused on GIS Web Service Composition. However, little research works concern on control mechanisms of improving availability and reliability in GIS Web Service Composition. Considering that GIS Web Services are in essence loosely-coupled and hosted by different providers. As a result, any update of any service, might affect critically. the overall composition consistency and execution; Moreover because most of geographic operations are CPU-intensive, it means that GIS Web Service Compositions consisting of basic geographic operations are more CPU-intensive will perhaps take several days to finish the execution of one sin-le GIS Web Service Composition! Without support of high availability and reliability, any mistake will lead to the failure of the whole composition execution and the waste of much computing resource. So availability and reliability in GIS Web Service Composition should be paid more attention. This paper proposes a mechanism of service compensation to achieve high availability and reliability in GIS Web Service Composition. The basic idea is that when one web service of composition fails, the execution of the whole composition is not aborted immediately; on the contrary, the compensation mechanism tries to find another web service which can provide the same function to "compensate" it. The abortion of composition only happens when the "compensating" web services can not be found or all of them fail.