ERRORS IN 'PROCESS SYNCHRONIZATION IN DATABASE SYSTEMS' by

This paper disproves several results pertaining to database concurrency control that are claimed in [8]. The results we disprove are • theorems 3.1, 3.2, 3.6-- which claim a polynomial time algorithm for testing whether transaction schedules are serializable, and • theorems 4.2 and 4.7-- which claim a necessary and suff ic ient mechanism for preserving the "weak consistency " of databases. In addition, we demonstrate that the notion of "weak consistency " introduced in [8] admits database states that are strictly inconsistent. I0 In a recent paper [8], G. Schlageter introduced a formal theory of database concurrency control that is similar in appearance to the seriali-zability theory developed in [1,2,3,5,6,7,9] and elsewhere. One of the results claimed in [8] implies that segializability of transaction schedule