Diane C. P. Smith

Database abstractions: aggregation and generalization

Two kinds of abstraction that are fundamentally important in database design and usage are defined. Aggregation is an abstraction which turns a relationship between objects into an aggregate object. Generalization is an abstraction which turns a class of objects into a generic object. It is suggested that all objects (individual, aggregate, generic) should be given uniform treatment in models of the real world. A new data type, called generic, is developed as a primitive for defining such models. Models defined with this primitive are structured as a set of aggregation hierarchies intersecting with a set of generalization hierarchies. Abstract objects occur at the points of intersection. This high level structure provides a discipline for the organization of relational databases. In particular this discipline allows: (i) an important class of views to be integrated and maintained; (ii) stability of data and programs under certain evolutionary changes; (iii) easier understanding of complex models and more natural query formulation; (iv) a more systematic approach to database design; (v) more optimization to be performed at lower implementation levels. The generic type is formalized by a set of invariant properties. These properties should be satisfied by all relations in a database if abstractions are to be preserved. A triggering mechanism for automatically maintaining these invariants during update operations is proposed. A simple mapping of aggregation/generalization hierarchies onto owner-coupled set structures is given.

Database abstractions: aggregation

Aggregation is introduced as an abstraction which is important in conceptualizing the real world. Aggregation transforms a relationship between objects into a higher-level object. A new data type, called aggregate, is developed which, under certain criteria of “well-definedness,” specifies aggregation abstractions. Relational databases defined as collections of aggregates are structured as a hierarchy of n-ary relations. To maintain well-definedness, update operations on such databases must preserve two invariants. Well-defined relations are distinct from relations in third normal form. It is shown that these notions are complementary and both are important in database design. A top-down methodology for database design is described which separates decisions concerning aggregate structure from decisions concerning key identification. It is suggested that aggregate types, and other types which support real-world abstractions without introducing implementation detail, should be incorporated into programming languages.

The design of a rotating associative memory for relational database applications

The design and motivation for a rotating associative relational store (RARES) is described. RARES is designed to enhance the performance of an optimizing relational query interface by supporting important high level optimization techniques. In particular, it can perform tuple selection operations at the storage device and also can provide a mechanism for efficient sorting. Like other designs for rotating associative stores, RARES contains search logic which is attached to the heads of a rotating head-per-track storage device. RARES is distinct from other designs in that it utilizes a novel “orthogonal” storage layout. This layout allows a high output rate of selected tuples even when a sort order in the stored relation must be preserved. As in certain other designs, RARES can usually output a tuple as soon as it is found to satisfy the selection criteria. However, relative to these designs, the orthogonal layout allows an order of magnitude reduction in the capacity of storage local to the search logic.

An approach to Stored Data Definition and Translation

The CODASYL Stored Data Definition and Translation Task Group has for the past two years been investigating the major components necessary in a language for data translation. Data translation is defined as the process whereby data that can be processed on one computer (the source file) can be translated into a form (the target file) which can be used by the same or a different processing system on a possibly different computer. Two languages are necessary—a Stored Data Definition Language to characterize the logical structure and physical realization of the source and target files, and a Translation Definition Language for defining how target file data instances are to be derived from source file data instances. This report discusses major components of each language and provides sample statements in terms of an example data translation from a COBOL file to a NIPS/360 file.

A Data Base Approach to Software Specification

A data base is a simulation of some real-world phenomena that is represented on a computing machine. A long-standing goal of data base technology has been to specify the semantics of the simulation while suppressing all details of its computer representation. To meet this goal, a variety of specification languages called data base models have been developed. These models are oriented towards applications where large quantities of intricately interrelated data are manipulated by multiple users.

1978 New Orleans Data Base Design Workshop Report

This is a summary of a bigger report based on the results arrived at the New Orleans data base design workshop. This paper outlines the four major areas of data base design. It discusses the important issues, some of the results which have been achieved and future research problems.

Database Program Conversion: A Framework For Research

As requirements change, database administrators come under pressure to change the schema which is a description of the database structure. Although writing a new schema is a relatively easy job and transforming the database to match the schema can be accomplished with a modest effort, transforming the numerous programs which operate on the database often requires enormous effort. This interim report describes previous research, defines the problem and proposes a framework for research on the automatic conversion of database programs to match the schema transformations. The approach is based on a precise description of the data structures, integrity constraints, and permissible operations. This work will help designers of manual and computer aided conversion facilities, database administrators who are considering conversions and developers of future database management systems, which will have ease of conversion as a design goal.

Data base abstraction

Real-world systems modelled by data bases are often quite complex. It is essential that the data base be structured in a way which supports a users abstractions about the real-world system. The “relation” data type is introduced as a structuring primitive for relational data bases The relation data type has similar abstraction properties to the “record” data type of PASCAL. A data base defined via relation data types is structured as a hierarchy of n-ary relations. It is shown that the consistency of this hierarchic structure can be preserved during update operations by two simple rules. A top-down methodology for data base design with relation data types is developed. This methodology minimizes the number of details with which a designer must contend at one time. In particular, the methodology allows the separation of decisions concerning abstract structure from decisions concerning key identification. The separation simplifies both types of decision making for the data base designer.

The design of a rotating associative array memory for a relational data base management application

There are significant advantages to tailoring hardware storage devices to support high level data models in very large data bases. A storage device that can assume some of the data selection functions traditionally performed by the CPU can substantially reduce the amount of data to be transferred to the CPU. This reduction together with increased concurrency of CPU and device operation result in increased data rates and lowor response times By designing the device to support one specific data model, greator efficiency can be achieved than in devices dosigned to be a compromise in their support of several different models. The number and complexity Of the functions performed by the device can be drastically reduced, along with its development and production costs. In this paper we describe the design and usage Of an associative array memory using a rotating storage device which is tailored to support the relational model of E. F. Codd.

Using an iTouch to Teach Core Curriculum Words and Definitions: Efficacy and Social Validity

Media scholars have long recognized the interaction between the medium that conveys the information and the information that is conveyed. This study examined the relative impact of different low- and high-tech instructional mediums (e.g., flashcards and the iTouch) on the acquisition of general education content-referenced sight words and definitions by students with significant cognitive disabilities. Results indicated that most of the students (three of the four students in the study) preferred high-tech instructional mediums during preference assessments prior to instruction. There was an increase in the tolerance for massed trials for preferred instructional mediums, but it was not meaningful. In spite of these data, there was minimal difference in the rates of skill acquisition or the social validity of the instructional mediums.