Extended OQL for Object Oriented Parallel Query Processing
Data Science Journal
Herein, an extension to the object query language (OQL) for incorporating binary relational expressions is investigated. The extended query language is suitable for query submissions to an object oriented database, whose functionality is based upon the algebra of binary relations. Algebraic expressions, consisting of simple and multiple merged chains of binary relations, are stated in SQL syntax-based object queries, which are utilized by a multiwavefront algorithm mapped on a multi-directional
... multi-functional engine(M 2 FE), for object oriented parallel query processing. The proposed extension also attempts to solve other object oriented database issues, such as inheritance, relationships between objects and literals, and recursive queries. Keywords: Object oriented databases, Object query language extension, Object oriented recursive queries, Parallel query processing, Algebra of binary relations Attempts to use the algebra of binary relations for object manipulation purposes resulted in graph-oriented systems, where graphs were used for querying object databases (Gyssens, 1994a; Gyssens, 1994b; Sarathy, 1993) or structural manipulation of software system architectures (Hold, 1998; Fahmy, 2000) . These graph systems obviously have serious disadvantages, because the large number of derived objects results in large scheme graphs, which are difficult to understand, handle or even to be displayed. To avoid graph complexities and disadvantages in querying object-oriented databases, an extension to the existing OQL (Cattell, 2000) for incorporating expressions of binary relations algebra in queries, is proposed. Because OQL has adopted the use of the SQL form, the algebraic expressions can be stated using SQL syntax, which can also facilitate users familiarized with legacy database systems. Connecting a series of binary relations through the algebraic composition operator, simple and multiple chains are formed. The multiple chains can be merged for query optimization purposes. These chains are stated in queries using SQL syntax. A multiwavefrontlike algorithm, which is mapped on a multi-directional multi-functional engine, is proposed for efficient query processing purposes. This algorithm (and engine) processes the simple and multiple merged chains of binary relations introduced in the OQL extension and stated in queries. The basic elements of the multi-functional engine architecture can be of two types of array processors: a (synchronous) square systolic device for wavefront-like computations -S 2 DWC (Fountoukis, 2004) or a bidirectional parallel cubic engine -BPCE (Fountoukis, 2005) .