CODASYL databases where created as part of the COBOL language standard. CODASYL stands for Conference On Data SYstems Languages. A CODASYL database uses pointers to link together data structures. Common data structures include the OOK for storing single values, linked lists for storing a fixed quantities of a know size, and BLOBs, Binary Large OBjects of arbitrary size. The CODASYL data model was adapted into several commercial products such as AdaBase and EagleSpeed RTDB.
CODASYL databases, sometimes called network model databases, have several differences from newer relational database model.
- They don’t use primary keys or foreign keys to associate data
- Data is instead linked using sets. By retrieving the set data structure you can get pointers to all the member elements.
- It is very easy to load all of the pointers into RAM and provide hard real time limits on transactions
The invention of SQL signaled the end of the network data model. SQL’s standard, easy to use, syntax was very powerful. A problem that would take pages of network model coding can be written in one line of code in SQL.