Abstract: Fundamentally, semantic grid database is about bringingglobally distributed databases together in order to coordinate resourcesharing and problem solving in which information is given well-definedmeaning, and DartGrid II is the implemented database gird system whosegoal is to provide a semantic solution for integrating databaseresources on the Web. Although many algorithms have been proposed foroptimizing query-processing in order to minimize costs and/or responsetime, associated with obtaining the answer to query in a distributeddatabase system, database grid query optimization problem isfundamentally different from traditional distributed queryoptimization. These differences are shown to be the consequences ofautonomy and heterogeneity of database nodes in database grid.Therefore, more challenges have arisen for query optimization indatabase grid than traditional distributed database. Following thisobservation, the design of a query optimizer in DartGrid II is presented,and a heuristic, dynamic and parallel query optimization approach toprocessing query in database grid is proposed. A set of semantic toolssupporting relational database integration and semantic-basedinformation browsing has also been implemented to realize the above vision.