No abstract

In this paper we survey, consolidate, and present the state of the art in distributed database concurrency control. The heart of our analysts is a decomposition of the concurrency control problem into two major subproblems: read-write and write-write synchronization. We describe a series of synchromzation techniques for solving each subproblem and show how to combine these techniques into algorithms for solving the entire concurrency control problem. Such algorithms are called "concurrency control methods." We describe 48 principal methods, including all practical algorithms that have appeared m the literature plus several new ones. We concentrate on the structure and correctness of concurrency control algorithms. Issues of performance are given only secondary treatment.

The semi-join is a relational algebraic operation that selects a set of tuples in one relation that match one or more tuples of another relation on the joining domains. Semi-joins have been used as a basic ingredient in query processing strategies for a number of hardware and software database systems. However, not all queries can be solved entirely using semi-joins. In this paper the exact class of relational queries that can be solved using semi-joins is shown. It is also shown that queries outside of this class may not even be partially solvable using "short" semi-join programs. In addition, a linear-time membership test for this class is presented.KEY WORDS AND PHRASES: semi-join, relational database, relational query processing cR CATEGORIES: 3.74, 4.33, 5.25

Problems related to functional dependencies and the algorithmic design of relational schemas are examined. Specifically, the following results are presented: (1) a tree model of derivations of functional dependencies from other functional dependencies; (2) a linear-time algorithm to test if a functional dependency is in the closure of a set c,f functional dependencies; (3) a quadratic-time implementation of Bernstein's third normal form schema synthesis algorithm.Furthermore, it is shown that most interesting algorithmic questions about Boyce-Codd normal form and keys are &?-complete and are therefore probably not amenable to fast algorithmic solutions.

Most relational database systems provide a facility for supporting user views. Permitting this level of abstraction has the danger, however, that update requests issued by a user within the context of his view may not translate correctly into equivalent updates on the underlying database. The purpose of this paper is to formalize the notion of update translation and derive conditions under which translation procedures will produce correct translations of view updates.