A data allocation algorithm for distributed hypermedia documents

Abstract

A major cost in executing queries in a distributed database system is the data transfer cost incurred in transferring relations (fragments) accessed by a query from different sites to the site where the query is initiated. The objective of a data allocation algorithm is to locate the fragments at different sites so as to minimize the total data transfer cost incurred in executing a set of queries. This is equivalent to minimizing the average query execution time, which is of primary importance in a wide class of distributed systems. The data allocation problem, however, is NP-complete, and thus requires fast heuristics to generate efficient solutions. The problem becomes more complex in the context of hypermedia documents (Web pages), within which the multimedia data objects (MDOs) need to be synchronized during presentation to the end users. Since the basic problem of data allocation in distributed database systems is NP-complete, we need heuristics which can generate near-optimal MDO allocations. In this paper, we propose a navigational model to represent hypermedia documents and their access behaviour from end users. We also formulate the problem by developing a base-case cost model for the response time, and we design an algorithm to find near-optimal solutions for allocating MDOs of the hypermedia documents while adhering to the synchronization requirements. We compare the algorithmic solution with an exhaustive solution over a set of experiments.