Brief History of the Relational Model
The relational model was first proposed by E. F. Codd in his seminal paper ‘A relational
model of data for large shared data banks’ (Codd, 1970). This paper is now generally
accepted as a landmark in database systems, although a set-oriented model had been
proposed previously (Childs, 1968). The relational model’s objectives were specified as
follows:
n To allow a high degree of data independence. Application programs must not be
affected by modifications to the internal data representation, particularly by changes to
file organizations, record orderings, or access paths.
n To provide substantial grounds for dealing with data semantics, consistency, and redundancy
problems. In particular, Codd’s paper introduced the concept of normalized
relations, that is, relations that have no repeating groups. (The process of normalization
is discussed in Chapters 13 and 14.)
n To enable the expansion of set-oriented data manipulation languages.
Although interest in the relational model came from several directions, the most significant
research may be attributed to three projects with rather different perspectives. The first of
these, at IBM’s San José Research Laboratory in California, was the prototype relational
DBMS System R, which was developed during the late 1970s (Astrahan et al., 1976). This
project was designed to prove the practicality of the relational model by providing an
implementation of its data structures and operations. It also proved to be an excellent
source of information about implementation concerns such as transaction management,
concurrency control, recovery techniques, query optimization, data security and integrity,
human factors, and user interfaces, and led to the publication of many research papers and
to the development of other prototypes. In particular, the System R project led to two
major developments:
n the development of a structured query language called SQL (pronounced ‘S-Q-L’, or
sometimes ‘See-Quel’), which has since become the formal International Organization
for Standardization ( ISO) and de facto standard language for relational DBMSs;
n the production of various commercial relational DBMS products during the late 1970s
and the 1980s: for example, DB2 and SQL/DS from IBM and Oracle from Oracle
Corporation.
The second project to have been significant in the development of the relational model
was the INGRES (Interactive Graphics Retrieval System) project at the University of
California at Berkeley, which was active at about the same time as the System R project.
The INGRES project involved the development of a prototype RDBMS, with the research
concentrating on the same overall objectives as the System R project. This research led
to an academic version of INGRES, which contributed to the general appreciation of
relational concepts, and spawned the commercial products INGRES from Relational
Technology Inc. (now Advantage Ingres Enterprise Relational Database from Computer
Associates) and the Intelligent Database Machine from Britton Lee Inc.
The third project was the Peterlee Relational Test Vehicle at the IBM UK Scientific
Centre in Peterlee (Todd, 1976). This project had a more theoretical orientation than the
System R and INGRES projects and was significant, principally for research into such
issues as query processing and optimization, and functional extension.
Commercial systems based on the relational model started to appear in the late
1970s and early 1980s. Now there are several hundred RDBMSs for both mainframe
and PC environments, even though many do not strictly adhere to the definition of the
relational model. Examples of PC-based RDBMSs are Office Access and Visual FoxPro
from Microsoft, InterBase and JDataStore from Borland, and R:Base from R:BASE
Technologies.
Owing to the popularity of the relational model, many non-relational systems now
provide a relational user interface, irrespective of the underlying model. Computer Associates’
IDMS, the principal network DBMS, has become Advantage CA-IDMS, supporting
a relational view of data. Other mainframe DBMSs that support some relational features
are Computer Corporation of America’s Model 204 and Software AG’s ADABAS.
Some extensions to the relational model have also been proposed; for example,
extensions to:
n capture more closely the meaning of data (for example, Codd, 1979);
n support object-oriented concepts (for example, Stonebraker and Rowe, 1986);
n support deductive capabilities (for example, Gardarin and Valduriez, 1989).
We discuss some of these extensions in Chapters 25–28 on Object DBMSs.
The relational model was first proposed by E. F. Codd in his seminal paper ‘A relational
model of data for large shared data banks’ (Codd, 1970). This paper is now generally
accepted as a landmark in database systems, although a set-oriented model had been
proposed previously (Childs, 1968). The relational model’s objectives were specified as
follows:
n To allow a high degree of data independence. Application programs must not be
affected by modifications to the internal data representation, particularly by changes to
file organizations, record orderings, or access paths.
n To provide substantial grounds for dealing with data semantics, consistency, and redundancy
problems. In particular, Codd’s paper introduced the concept of normalized
relations, that is, relations that have no repeating groups. (The process of normalization
is discussed in Chapters 13 and 14.)
n To enable the expansion of set-oriented data manipulation languages.
Although interest in the relational model came from several directions, the most significant
research may be attributed to three projects with rather different perspectives. The first of
these, at IBM’s San José Research Laboratory in California, was the prototype relational
DBMS System R, which was developed during the late 1970s (Astrahan et al., 1976). This
project was designed to prove the practicality of the relational model by providing an
implementation of its data structures and operations. It also proved to be an excellent
source of information about implementation concerns such as transaction management,
concurrency control, recovery techniques, query optimization, data security and integrity,
human factors, and user interfaces, and led to the publication of many research papers and
to the development of other prototypes. In particular, the System R project led to two
major developments:
n the development of a structured query language called SQL (pronounced ‘S-Q-L’, or
sometimes ‘See-Quel’), which has since become the formal International Organization
for Standardization ( ISO) and de facto standard language for relational DBMSs;
n the production of various commercial relational DBMS products during the late 1970s
and the 1980s: for example, DB2 and SQL/DS from IBM and Oracle from Oracle
Corporation.
The second project to have been significant in the development of the relational model
was the INGRES (Interactive Graphics Retrieval System) project at the University of
California at Berkeley, which was active at about the same time as the System R project.
The INGRES project involved the development of a prototype RDBMS, with the research
concentrating on the same overall objectives as the System R project. This research led
to an academic version of INGRES, which contributed to the general appreciation of
relational concepts, and spawned the commercial products INGRES from Relational
Technology Inc. (now Advantage Ingres Enterprise Relational Database from Computer
Associates) and the Intelligent Database Machine from Britton Lee Inc.
The third project was the Peterlee Relational Test Vehicle at the IBM UK Scientific
Centre in Peterlee (Todd, 1976). This project had a more theoretical orientation than the
System R and INGRES projects and was significant, principally for research into such
issues as query processing and optimization, and functional extension.
Commercial systems based on the relational model started to appear in the late
1970s and early 1980s. Now there are several hundred RDBMSs for both mainframe
and PC environments, even though many do not strictly adhere to the definition of the
relational model. Examples of PC-based RDBMSs are Office Access and Visual FoxPro
from Microsoft, InterBase and JDataStore from Borland, and R:Base from R:BASE
Technologies.
Owing to the popularity of the relational model, many non-relational systems now
provide a relational user interface, irrespective of the underlying model. Computer Associates’
IDMS, the principal network DBMS, has become Advantage CA-IDMS, supporting
a relational view of data. Other mainframe DBMSs that support some relational features
are Computer Corporation of America’s Model 204 and Software AG’s ADABAS.
Some extensions to the relational model have also been proposed; for example,
extensions to:
n capture more closely the meaning of data (for example, Codd, 1979);
n support object-oriented concepts (for example, Stonebraker and Rowe, 1986);
n support deductive capabilities (for example, Gardarin and Valduriez, 1989).
We discuss some of these extensions in Chapters 25–28 on Object DBMSs.
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