Fujitsu UDS/SQL V2.5 2.2 Data models

CODASYL model General information

28 U929-J-Z125-9-76

2.2 Data models

The UDS/SQL database system supports both the network model (CODASYL model) and

the relational model. It encompasses the principles and capabilities of both the CODASYL

and the relational models in a single system. UDS/SQL can be regarded as the imple men-

tation of a coexistence model of a database. The following sections briefly desc ribe the

CODASYL model, the relational model, the relative merits of the two models, and the

coexistence model.

A major user demand is that database systems are c ompatible. The standardization of

database systems has thus been the goal of powerful user associatio ns for many years.

The Conference on Data System Languages (CODASYL) has developed widely accepted

recommendations for the standardization of database systems. This association is already

well-known for its achievements in application portability thanks to its development of the

programming language COBOL.

CODASYL was constituted in 1959 by US producers and users, and, notably, with the

participation of the US Administration.

Since 1965, this association has concentrated partly on data organization and databases.

When the basic results of the different study groups were published, they desc ribed a

database concept which has been continually improved.

The CODASYL model provided the basis for the implementation of the UDS/SQL database

system.

In the CODASYL model, a database contains not only records, but also the relationships

between the records. This is why it is also referred to as the network model.

The following diagram (figure 2) shows an example of a networked data structure, which is

represented by boxes and arrows. A box symbolizes a type of record. In this example, the

records that describe the suppliers are grouped together in the reco rd type SUPPLIER. All

records of the given record type have the same structure. For each supplier, the SUPPLIER

record type contains a record which defines the name and th e city of that supplier. NAME

and CITY are record elements names.

Another record type shown in figure 2 is the record type ARTICLE. The record types

ARTICLE and SUPPLIER are connected by an arrow, which indicates that a relationship

exists between the record types. Such relationships are referred to as set relationship s or

simply sets.