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Co-existing data base management systems (CODASYL DBTG and System R approaches)
The paper addresses the problem of communication between co-existing DBMSs. Specifically, two data models--that is, the Network and Relationals models--have been analyzed using their respective implementations CODASYL DBTG and System R.
Feasibility of communication is discussed and mapping mechanisms are suggested between the two DBMSs at the following levels:
- Data Model
- Data Definition Language
- Data Manipulation Language
- Access method
Restrictions arising from the individual data models in the mapping process have been outlined, in particular the levels at which communication takes place between the two systems: from Network to Relational at the query language level and the converse at the access method level
Viaduct : an interactive, very-high-level data manipulation language for a microcomputer-based database system.
Bibliography: leaves 203-210.A very-high-level data manipulation language for a database system is one in which the user specifies in non-procedural terms the operations that are to be performed on the data stored in the database; the actual method by which the operations are executed does not concern the user. VIADUCT provides such an interface to a microcomputer-based database system known as MDBS. Thus VIADUCT allows a microcomputer user lacking in computer sophistication to interact with, and derive the benefits of, a powerful database management system. Additional security restrictions and integrity constraints usually found only on mainframe database management systems are provided by VIADUCT through the mechanism of a subschema generator
The semantic database model as a basis for an automated database design tool
Bibliography: p.257-80.The automatic database design system is a design aid for network database creation. It obtains a requirements specification from a user and generates a prototype database. This database is compatible with the Data Definition Language of DMS 1100, the database system on the Univac 1108 at the University of Cape Town. The user interface has been constructed in such a way that a computer-naive user can submit a description of his organisation to the system. Thus it constitutes a powerful database design tool, which should greatly alleviate the designer's tasks of communicating with users, and of creating an initial database definition. The requirements are formulated using the semantic database model, and semantic information in this model is incorporated into the database as integrity constraints. A relation scheme is also generated from the specification. As a result of this research, insight has been gained into the advantages and shortcomings of the semantic database model, and some principles for 'good' data models and database design methodologies have emerged
Evaluation of Functional Data Models for Database Design and Use
The problems of design, operation, and maintenance of databases using the three most
popular database management systems (Hierarchical, CQDASYL/DBTG, and Relational) are
well known. Users wishing to use these systems have to make conscious and often complex
mappings between the real-world structures and the data structuring options (data models)
provided by these systems. In addition, much of the semantics associated with the data
either does not get expressed at all or gets embedded procedurally in application programs in
an ad-hoc way.
In recent years, a large number of data models (called semantic data models) have been
proposed with the aim of simplifying database design and use. However, the lack of usable
implementations of these proposals has so far inhibited the widespread use of these concepts.
The present work reports on an effort to evaluate and extend one such semantic model by
means of an implementation. It is based on the functional data model proposed earlier by
Shipman[SHIP81). We call this 'Extended Functional Data Model' (EFDM).
EFDM, like Shipman's proposals, is a marriage of three of the advanced modelling concepts
found in both database and artificial intelligence research: the concept of entity to represent
an object in the real world, the concept of type hierarchy among entity types, and the
concept of derived data for modelling procedural knowledge. The functional notation of the
model lends itself to high level data manipulation languages. The data selection in these
languages is expressed simply as function application. Further, the functional approach makes
it possible to incorporate general purpose computation facilities in the data languages without
having to embed them in procedural languages. In addition to providing the usual database
facilities, the implementation also provides a mechanism to specify multiple user views of the
database
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