Network Model

      The network model is a record based data model.  A record based model is used to describe external and conceptual level of a database and describe some extent of an internal level of a database.  In record based data model database consist of records and these records may be of different types. In network model records are stored as a multiple parent child relationship as compare to hierarchical model. In network model the relationship between records is known as sets. The network model is developed to over the problem of hierarchical model. The structure and language constructs of network model is define by conference On Data Systems Language (CODASYL).

The example of a network data model is:

                                              Figure: The network model

Characteristics of network model:

                                                A network model has different characteristics.  The characteristics of a network database management system are as follow:

1.    Data record typed are represented as network

                                                   In network model the record types are stored or represented as a network.

2.    Each sub-module can have one or more super-modules

                                                           The network model supports a multiple parent child relationship. Each child record type in a network model could have one or more parent record types.

3.    Represents a set of related records

                                         The structures of a records and sets have to be defined in advance.

4.    Complex structure

                              The structure of a database is complex because network model support multiple parent child relationship.

5.    Relationships are predefined

                                          Network model support multiple parent child relationship. The relationship is specified in advance. The network model is not very flexible but has a high performance level.

6.    Difficult to reorganize

                                The insertion and deletion of records in a database is involves a pointers and changing suitable links between records. The network model database is difficult to reorganize because to maintain a links between records is difficult.

7.    Navigation done by programmer

                                                 The 3 generation language (3GL) program is written to navigate in a database. To access a particular record, the record by record navigation is required.

8.    3 generation language inadequate for handling sets

                                                        The major drawback of using network model is using 3GLs. In network model the records are processed as a set. 3GLs handle only one record at a time and hence 3GL is inadequate for handling the sets.

9.       Query facility not available

                                     Query facility is not available in network database management system. 3GL program is written to specify the path and relationship.