An entity-based approach to query processing in relational databases: Part I: Entity type representation

摘要

An entity-based query interface to relational databases is developed. The interface combines some object-oriented features with the strengths of universal relation DBMSs (UR-DBMSs) by a value-oriented high-level representation of complex entity types. It enhances logical data independence by hiding their implementation in a relational database. The abstraction level of the entity representation lies between the relations of the relational model and the universal relation. This allows higher level expressions than the relational model but avoids the weaknesses of the UR-DBMSs. The interface supports a declarative entity-based query language of the level of Quel (described in Part II). The key features of the interface are: (1) the entity type representation and associated operations which allow the derivation of the entity types of the results of entity-based queries, and (2) and unambiguous and optimizing solution to the query interpretation problem of UR-DBMSs. The interface constructs equivalent RA expressions for entity queries to be evaluated by relational DBMSs (RDBMSs).The interface is specified in a formal and general way. It has essential benefits, which support further processing of query results, improve query efficiency, clarify query semantics, enhance logical data independence, and allow use of existing RDBMS software by interfacing them to the entity level processing in a systematic way. It separates the entity type and relational levels into different domains and integrates them together through a well-defined interface. The interface exploits fully and easily the optimization capabilities of universal relation-based systems.The entity types provide the users with a high-level and natural view of the database. The users express their queries in terms of the entity types. This simplifies the expression of complex queries considerably w.r.t. conventional query systems. The interface exploits this knowledge in an effective way.