To overcome the problems of the hierarchical data model, the Network Model was developed. The network model modified the hierarchical model by allowing multiple parent-child relationships. These relationships are known as sets in a network model. The network model structures and language constructs were defined by the CODASYL (Conference on Data Systems Language).
The Network Model
1. Characteristics of Network Model:
The characteristics of a network DBMS are:
2. Data record types are represented as a network:
In this model, data record types are represented as a network.
3. Each sub-module can have one or more super-modules:
Since multiple parent-child relationships are supported, child (sub-module) record type could have more than one parent (super) record types.
4. Represents a set of related records:
The sets that support multiple parent-child relationships and the structure of the records have to be specified in advance.
5. Complex Structure:
Since multiple parent-child relationships are supported, database structure
becomes very complicated.
6. Relationships are Pre-defined:
The network database implements sets that support multiple parent-child relationships. The sets have to be specified in advance. In the tradeoff between flexibility and performance, a network model is not very flexible to reorganize hut has high performance Levels.
7. Difficult to reorganize:
The network database is very difficult to be reorganized because inserting or deleting a record would involve tracing the pointers and changing the appropriate links.
8. Navigation done by the programmer:
The programmer will have to write 3GL programs for specifying the relationship and direction to navigate into the database. To access records, the programmer has to navigate the database record-by-record.
9. 3GL Inadequate for Handling Sets:
The records in a network model are processed one set at a time. 3GLs handle only one record at a time and hence are inadequate for handling the sets.
10. Query Facility not Available:
Network database management systems do not have any query facility. So 3GL programs will have to he written specifying the path and the relationship.
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