A TWO-LEVEL METADATA DICTIONARY APPROACH FOR SEMANTIC QUERY PROCESSING IN MULTIDATABASE SYSTEMS

作     者：MIIN-JENG PAN SHI-KUO CHANG CHIEN-CHIAO YANG 

作者机构：Department of Electronic Engineering National Taiwan Institute of Technology 43 Keelung Road Section 4 Taipei 10772 Taiwan R.O.C. phone: (412)–624–8423 fax: (412)–624–8465. Department of Computer Science University of Pittsburgh Pittsburgh PA 15260 USA 

出 版 物：《International Journal of Software Engineering and Knowledge Engineering》 

年 卷 期：1993年第3卷第2期

页      面：231-255页

学科分类：08[工学] 0812[工学-计算机科学与技术（可授工学、理学学位）] 

主　　题：multidatabase system metadata dictionary Horn clause database integration deductive database system semantic query optimization 

摘      要：A multidatabase system (MDBS) is a system that integrates several autonomous database systems and provides users with a uniform access to all the databases. In this paper we developed a two-level active metadata dictionary approach for semantic query processing. To capture the global view of data schemas of participating databases which may be heterogeneous, a Hornclause data model is used. The lower-level metadata dictionaries (LLMDs) keep metadata for each corresponding local database in MDBS. The higher-level metadata dictionary (HLMD) integrates the metadata about all LLMDs. The database integration strategy includes two phases: schema translation and schema integration. It is a bottom-up approach integrating schema from the underlying database schemas. The evaluation strategy is a top-down approach. It starts with a query as a global goal to be achieved, unifies and optimizes the query to decompose the goal into subgoals that can be evaluated against extensional database, then translates these subgoals into corresponding queries against underlying DBMSs. To solve the control problem, we employ a G-net model for procedure control and inference control. An experimental implementation in Prolog is described.