Bases De Datos Distiibuidas

ABSTRACTS

from other ACM Publications
consequences of base relation constraints. A technique for determming such valid view constraints is presented in tbis paper. A generalization of the tableau chase is used The idea of the method is to generate a tableau for the expression whose summary violates the test constraint in a "canonical" way. The case then tries to remove this violation. It isalso shown how this method has applications to schema design. Relations not in normal form or havmg other deficiencies can be replaced by normal form projections without losing the ability to represent all constraint information. Categories and Subject Descriptors: H.2.! [Database Management]: Logical Design—schema and subschema General Terms: Algorithms, Theory Additional Key Words and Phrases:Relational algebra, dependencies, tableaux, chase, relational model For Correspondence: A Klug, Computer Sciences Department, University of Wisconsin-Madison, Madison, WI 53706.

In the ACM Transactions on Database Systems/September Issue
Transactions and Consistency in Distributed Database Systems by Irving L. Traiger, Jim Gray, Cesare A. Galtieri, and Bruce G. Lindsay
The concepts oftransaction and of data consistency are defmed for a distributed system. The cases of partitioned data, where fragments of a file are stored at multiple nodes, and replicated data, where a fde is replicated at several nodes, are discussed. It is argued that the distribution and replication of data should be transparent to ihe programs which use tbe data. That is, the programming i^nterface should providelocation transparency, replica transparency, concurrency transparency, and failure transparency. Techniques for providing such transparencies are abstracted and discussed. By extending the notions of system schedule and system clock to handle multiple nodes, it is shown that a distributed system can be modeled as a single sequential execution sequence. This model is then used to discuss simpletechniques for implementing the various forms of transparency. Categories and Subject Descriptors: H.2.4 [Database Management]: Systems—distributed systems, transaction processing General Terms: None Additional Key Words and Phrases: Data replication, data partitioning, concurrency control, recovery For Correspondence: I.L. Traiger, IBM Research Laboratory, San Jose, CA 95193.

On the CorrectTranslation of Update Operations on Relational Views by Umeshwar Dayal and Philip A. Bernstein
Most relational database systems provide a facility for supporting user views. Permitting tbis 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 thispaper is to formalize the notion of update translation and derive conditions under which translation procedures will produce correct translations of view updates. Categories and Subject Descriptors: H.2.1 [Database Maoagement|: Logical Design^—schema and subschema: H.23. [Database Management]: Languages—data maniputation tanguages (DML): H.2.4 [Database Management]: Systems; H.2.5 [DatabaseManagement]: Heterogeneous Databases^—program translation: 1.2.2 [Artificial IntelligeDcej: Automatic Programming—/jro^ram transformation General Terms: Theory Additional Key Words and Phrases; User views, extemal schemata, relational databases, update translation, schema mapping For Correspondence: U. Dayal, Computer Corporation of America, 575 Technology Square, Cambridge, MA 02139.

A SimplifiedUniversal Relation Assumption and Its Properties by Ronald Fagin, Alberto O. Mendelzon, and Jeffrey D. UUman
One problem concerning the universal relation assumption is the inability of known methods to obtain a database scheme design in the general case, where the real-world constraints are given by a set of dependencies that includes embedded multivalued dependencies. We propose a simpler...