Kapali P. Eswaran

The notions of consistency and predicate locks in a database system

In database systems, users access shared data under the assumption that the data satisfies certain consistency constraints. This paper defines the concepts of transaction, consistency and schedule and shows that consistency requires that a transaction cannot request new locks after releasing a lock. Then it is argued that a transaction needs to lock a logical rather than a physical subset of the database. These subsets may be specified by predicates. An implementation of predicate locks which satisfies the consistency condition is suggested.

System R: relational approach to database management

System R is a database management system which provides a high level relational data interface. The systems provides a high level of data independence by isolating the end user as much as possible from underlying storage structures. The system permits definition of a variety of relational views on common underlying data. Data control features are provided, including authorization, integrity assertions, triggered transactions, a logging and recovery subsystem, and facilities for maintaining data consistency in a shared-update environment. This paper contains a description of the overall architecture and design of the system. At the present time the system is being implemented and the design evaluated. We emphasize that System R is a vehicle for research in database architecture, and is not planned as a product.

SEQUEL 2: a unified approach to data definition, manipulation, and control

SEQUEL 2 is a relational data language that provides a consistent, English keyword-oriented set of facilities for query, data definition, data manipulation, and datac ontrol. SEQUEL 2 may be used either as a stand-alone interface for nonspecialists in data processing or as a data sublanguage embedded in a host programming language for use by application programmers and data base administrators. This paper describes SEQUEL 2 and the means by which it is coupled to a host language.

Storage and access in relational data bases

A model of storage and access to a relational data base is presented. Using this model, four techniques for evaluating a general relational query that involves the operations of projection, restriction, and join are compared on the basis of cost of accessing secondary storage. The techniques are compared numerically and analytically for various values of important parameters. Results indicate that physical clustering of logically adjacent items is a critical performance parameter. In the absence of such clustering, methods that depend on sorting the records themselves seem to be the algorithm of choice.

Collision-Free Access Control for Computer Communication Bus Networks

This paper considers access control for local area computer communication networks. We propose two distributed access control schemes for a bus network. The schemes are simple and asynchronous, and provide for collision-free communication among ports. In addition, one of the schemes provides a bounded, guaranteed time to transmisidon for each port. We also show that this scheme is efficient in the use of the bus bandwidth, in the sense that there is only a small fraction of time during which the bus is idle when there is at least one packet available for transmission.

An encoding method for multifield sorting and indexing

Sequences of character strings with an order relation imposed between sequences are considered. An encoding scheme is described which produces a single, order-preserving string from a sequence of strings. The original sequence can be recovered from the encoded string, and one sequence of strings precedes another if and only if the encoding of the first precedes the encoding of the second. The strings may be variable length, without a maximum length restriction, and no symbols need be reserved for control purposes. Hence any symbol may occur in any string. The scheme is useful for multifield sorting, multifield indexing, and other applications where ordering on more than one field is important.

Simplified odd-even sort using multiple shift-register loops

By using anN-loop shift-register structure called a uniform ladder,N records can be sorted by a simplified adaptation of the odd-even transposition-sort algorithm to finish in (N + 1)/2 loop times (periods) using (N − 1) comparators. The sorting can be overlapped with input/output; the percentage of unoverlapped sorting times is less than 20% of the total time with a single ladder, less than 6% using two ladders, and is zero with a sufficient number of ladders.