MODELLING DATA
All organizations need to
store the information and this is done through database. Data models refer to
the conceptual model of the data and the underlying relationships among them.
DBMS abstract some generic structures to represent conceptually every possible
file structure.
Data models can be
classified in two classes viz; Record-based logical Models and Object-based
logical models. Record-Based logical data models can be classified (Sadgopan,
1997) into the following categories:
Hierarchical Models: These are the early data models used in 1970’s. Hierarchical
models capture the intuitive hierarchy of the data elements. The early generation
of large DBMS e.g. IMS belongs to the hierarchical data models. Even today some
large databases are maintained on IMS platform.
Network Models: Since hierarchical models are unable to represent data items
that existing at two different level of hierarchy, network models were
proposed. The notable systems built using this model were ADABAS and DBMS-10 on
DEC-10 machines.
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Relational Models: Though network models were quite powerful, they lacked in elegance. The systems
built on this data model were dBase, Xbase and ORACLE. Almost all commercial
systems presently available like Oracle 8i, 9i, 11 etc., SQL Server, MySQL are built
on the relational models. There are 12 rules that are required to be followed
in a relational model.
