Graph-Based Protocols Graph-based protocols are an alternative to two-phase locking Impose a partial ordering->on the set D={d,d2,...,dh}of all data items. If d;->d;then any transaction accessing both d;and d;must access d;before accessing di. Implies that the set D may now be viewed as a directed acyclic graph,called a database graph. The tree-protocol is a simple kind of graph protocol. Database System Concepts-5th Edition,Oct 5,2006 16.16 @Silberschatz,Korth and SudarshanDatabase System Concepts - 5 16.16 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Graph-Based Protocols Graph-based protocols are an alternative to two-phase locking Impose a partial ordering → on the set D = {d1 , d2 ,..., dh } of all data items. If di → dj then any transaction accessing both di and dj must access di before accessing dj . Implies that the set D may now be viewed as a directed acyclic graph, called a database graph. The tree-protocol is a simple kind of graph protocol