Transaction Control Mechanism for the Object Cache Interface of R²D^2*

Abstract

R²D² is an object-oriented database system intended for engineering applications that is based on the nested relational data model. R²D² provides a two layer architecture for engineering application programming: a public database to globally store the engineering objects and a private database consisting of a local database and an object cache that are local to the application program. This paper is concerned with the transaction control mechanisms needed to control concurrent transactions that access the public database system. Objects are requested by a transaction to be transferred from the public database into the transaction's local database connected with an object cache, which together form the private data repository. Upon release of the objects from the cache they are checked back into the public database. The central implementation idea forms a modified intention locking scheme to provide for a high level of concurrency in accessing objects that are represented in nested relational structure, the underlying data model of R²D². This scheme facilitates the (exclusive or shared) locking of subobjects within an abstraction hierarchy while the remainder of the hierarchical object is still accessible by other transactions.