Analysis of Query Optimization Technique over Web Services

The query optimizer is the component of a database management system that attempts to determine the most efficient way to execute a query. The high quality, structured data from Web structured sources is invaluable for many applications. A critical but still largely unresolved question is: how to efficiently acquire the structured information inside Web databases through iteratively issuing meaningful queries? So, a general purpose Web Service Management System (WSMS) that enables querying multiple web services in a transparent and integrated fashion is analyzed. This paper tackles a first basic WSMS problem: query optimization for Select-Project-Join queries spanning multiple web services. Our main result is an algorithm for arranging a query’s web service calls into a pipelined execution plan that optimally exploits parallelism among web services to minimize the query’s total running time. Surprisingly, the optimal plan can be found in polynomial time even in the presence of arbitrary precedence constraints among web services, in contrast to traditional query optimization where the analogous problem is NP-hard.