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Data Models

Data Models: Whether entity relationship is represented by links or tuples

Three main data models are:

Hierarchical Model

  • Period: 1960
  • Approach: Records are arranged in inverted tree like structure with relationship in one direction and there can be only one parent
  • Disadvantages: 1. Rigid parent-child structure 2. Difficult navigation pro grammatically
  • E.g. IBM IMS
Network Model
  • Period: 1970
  • Approach: Records are arranged in networked node fashion. i.e. same as hierarchical with multiple parents
  • Disadvantages: More flexible navigation (because of bi-directional relationship)but still changes to database and application are still complicated
  • In both above models, structure is hard-wired in the application program, so change in database means need to change using applications as well
  • E.g. CODYSL DBTG
Relational Model
  • Period: Late 1970 and 1980s
  • Approach: parent-child relationship of above models replaced with related tables comprising of rows and columns.
  • Advantage: Flexibility even with complex relationships. Relational database is independent of application
  • E.g. DB2, Oracle, SQL Server, MySQL
It is to be noted that databases based on hierarchical and network models still exist and are in use.