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File-Level Operations on Network Data Structures.
Abstract
The time and cost of implementing data processing applications can be greatly reduced through the use of software systems which provide language for the expression of file-level operations on data, i.e., operations whose operands are sets of records or entire files, such as report generation and sorting. Such systems, which have been referred to as self-contained systems or generalized file management systems, have characteristically been restricted to logical data structure classes no richer than hierarchies. This paper explores the extension of the concept of file-level operations to network structures, as exemplified by the CODASYL DDLC data structure class, on the assumption that such a facility will prove useful to certain types of users (e.g., data administrators) for certain types of data manipulation (e.g., data base creation and updating). The paper first outlines the general requirements which must be met in such a facility, and then describes a specific approach to the development of a language for such a facility.
In this paper we assert that the hierarchical view of data will continue to be popular for a broad class of applications and users. In particular, some of these applications require complex data manipulation which, heretofore, has been dealt with procedurally. In this light, a nonprocedural language, CONVERT, is proposed as a high-level DBMS interface. CONVERT is meant to provide users with a tool for performing complex data manipulation and query of hierarchical data abstractions, called “Forms”. Included in the paper are a description of the Form data abstraction and the CONVERT language, as well as a complete illustrative sample application.
In general, it can be said that there exists a large body of technical literature that covers a wide spectrum of problems related to the new and very important field of data base systems. There is no doubt that the relational data base approach provides a scientific foundation and a sound engineering discipline. In addition, it provides a theory for data analysis and data structuringa s well as a badly needed formalism in this highly significant area of computer science. A considerable literature has been generated by the very fact that the relational approach provides a scientific discipline in a field that has been governed by a haphazard approach for a long time. However, too many papers present concepts that may never go beyond the realm of academic interest. Despite the existence of some small-scale (experimental) implementations, additional evidence is needed to indicate the practicality and feasibility of such an approach in a large-scale data base environment.
In this paper we assert that the hierarchical view of data will continue to be popular for a broad class of applications and users. In particular, some of these applications require complex data manipulation which, heretofore, has been dealt with procedurally. In this light, a nonprocedural language, CONVERT, is proposed as a high-level DBMS interface. CONVERT is meant to provide users with a tool for performing complex data manipulation and query of hierarchical data abstractions, called “Forms”. Included in the paper are a description of the Form data abstraction and the CONVERT language, as well as a complete illustrative sample application.
A survey of the literature on Distributed Data Base Management Systems is presented. The problems associated with distributing data throughout a network are summarized into two major areas: Data Distribution and Data Transfer. Each area is described detailing some of the major proposed solutions to the problems therein. The intention here is to provide the reader with an overview and an extensive bibliography for further study on any aspect of Distributed DBMS.
The essential concepts of the relational data model are defined, and normalization, relational languages based on the model, as well as advantages and implementations of relational systems are discussed.
A data model is presented, based on the extension of the concept of a DBTG owner-coupled set to permit static and dynamic sets and a new kind of set referred to as a virtual set. The notion of connection fields is introduced, and it is shown how connection fields may be used to construct derived information bearing set names, and hence permit the specification of (dynamic) sets which are not predeclared in a schema. Virtual sets are shown to reflect the functional dependencies which can exist within a file. A technique which permits the data model to be fully described diagrammatically by extended Bachman diagrams is described. A predicate calculus for manipulation of this data model is presented. Expressions written in this calculus are compared with corresponding expressions in a relational predicate calculus, DSL ALPHA. An argument for the relational completeness of the language is given.
The emergence of a database technology in recent years has focused interest on the subject of data models. A data model is the class of logical data structures which a computer system or language makes available to the user for the purpose of formulating data processing applications. The diversity of computer systems and languages has resulted in a corresponding diversity of data models, and has created a problem for the user in selecting a data model which is in some sense appropriate to a given application. An evaluation procedure is needed which will allow the user to evaluate alternative models in the context of a specific set of applications. This paper takes a first step toward such a procedure by identifying the attributes of a data model which can be used as criteria for evaluating the model. Two kinds of criteria are presented: use criteria, which measure the usability of the model; and implementation criteria, which measure the implementability of the model and the efficiency of the resulting implementation. The use of the criteria is illustrated by applying them to three specific models: an n-ary relational model, a hierarchic model, and a network model.
Self-contained Facilities to Process Sub-structures of More Complex Network Structures
- T W Olle