Network Data Model
The Network Data Model is a database model that allows for more complex relationships than the simpler Hierarchical Data Model. It was designed to represent more accurately how real-world data relationships exist, where multiple parent records can have multiple child records, thus creating a network structure.
History and Development
- 1969: The Conference on Data Systems Languages (CODASYL) introduced the Database Task Group (DBTG) to develop standards for Database Management Systems. This group laid the foundation for the network data model.
- 1971: The DBTG released its report, defining what would become known as the DBTG model, which was essentially the first network data model. This model allowed for sets (analogous to relationships) where one record type could be an owner and another could be a member, allowing for many-to-many relationships.
Key Features
- Set Relationship: The core concept in the network model is the set, which defines a one-to-many relationship. Records are linked via sets where an owner record can have multiple member records, and a member can be linked to several owners.
- Record Types: Records are divided into different types, each representing a real-world entity or object.
- Pointer-Based Navigation: Navigation through the network is done via pointers, which link records to each other. This makes traversing the data structure complex but allows for very efficient direct access to related records.
- Schema and Subschema: The schema describes the entire database structure, while a subschema defines the part of the database accessible to a particular application or user, allowing for different views of the data.
Advantages
- More flexible than the hierarchical model, allowing for many-to-many relationships.
- Better represents complex data relationships.
- Efficient for handling data with interconnected relationships.
Disadvantages
- Complexity in managing and navigating the data due to the pointer system.
- Maintenance can be challenging due to the need to manage pointers.
- Not as intuitive or user-friendly for non-technical users.
Applications and Use
The Network Data Model was particularly popular in the 1970s and 1980s, with systems like IDMS (Integrated Database Management System) and DMS-1100 being prominent examples of implementations. While it has largely been supplanted by the Relational Model and subsequent models like Object-Oriented Model, the principles of the network model are still evident in modern graph databases.
External Links for Further Reading
Related Topics