Concurrent execution of Prolog transaction

Abstract

Information systems are composed of multiple heterogeneous database systems and workstations interconnected by communication networks. Users want to manipulate data in multiple database systems in a common form. In our system, database systems are viewed to be fact base systems (FBSs), which provide sets of Prolog ground unit clauses, and retrieval and update operations on them. Transactions composed of multiple update operations on facts are written as Prolog rule clauses. In the Prolog system, atoms in a goal clause are selected from left to right. This means read/write operations on facts are sequentially executed. In this paper, we try to execute the transaction in parallel by multiple FBSs. In the sequence of atoms in the Prolog transaction, we define two types of meaningful sequences, i.e. conflict and flow ones. In this paper, we present how to decompose transactions into subtransactions, each of which is locally executed by one FBS, so as to preserve the meaningful sequences in the transaction. Also, we show that any parallel execution of the subtransactions is free of deadlock on send-receive relations.