The declining cost of computer hardware and the increasing data processing needs of geographically dispersed organizations have led to substantial interest in distributed data management. SDD-1 is a distributed database management system currently being developed by Computer Corporation of America. Users interact with SDD-1 precisely as if it were a nondistributed database system because SDD-1 handles all issues arising from the distribution of data. These issues include distributed concurrency control, distributed query processing, resiliency to component failure, and distributed directory management. This paper presents an overview of the SDD-1 design and its solutions to the above problems. This paper is the first of a series of companion papers on SDD-1 (Bernstein and Shipman [2], Bernstein et al. [4], and Hammer and Shipman [14]).

This paper presents the reliability mechanisms of SDD-1, a prototype distributed database system being developed by the Computer Corporation of America. Reliability algorithms in SDD-1 center around the concept of the Reliable Network (RelNet). The RelNet is a communications medium incorporating facilities for site status monitoring, event timestamping, multiply buffered message delivery, and the atomic control of distributed transactions.This paper is one of a series of companion papers on SDD-1 [3,4, 6, 131.

SQUARE (Specifying ~ueries As Relational Expressions) is a set oriented data sublanguage for expressing queries (access, modification, insertion, and deletion) to a data base consisting of a collection of time-varying relations. The language mimics how people use relations or tables to obtain information.It does not require the sophisticated mathematical machinery of the predicate calculus (bound variables, quantifiers, etc.) in order to express simple references to tables. However, the language has been shown to be complete, i.e., any query expressible in the predicate calculus is expressible in SQUARE.I.

SQUARE (<u>S</u>pecifying <u>Q</u>ueries <u>A</u>s <u>R</u>elational <u>E</u>xpressions) is a set oriented data sublanguage for expressing queries (access, modification, insertion, and deletion) to a data base consisting of a collection of time-varying relations. The language mimics how people use relations or tables to obtain information. It does not require the sophisticated mathematical machinery of the predicate calculus (bound variables, quantifiers, etc.) in order to express simple references to tables. However, the language has been shown to be complete, i.e., any query expressible in the predicate calculus is expressible in SQUARE.

SQUARE (Specifying ~ueries As Relational Expressions) is a set oriented data sublanguage for expressing queries (access, modification, insertion, and deletion) to a data base consisting of a collection of time-varying relations. The language mimics how people use relations or tables to obtain information.It does not require the sophisticated mathematical machinery of the predicate calculus (bound variables, quantifiers, etc.) in order to express simple references to tables. However, the language has been shown to be complete, i.e., any query expressible in the predicate calculus is expressible in SQUARE.I.