The Hierarchical Model

Was developed in the 1960s. The Hierarchical model was essentially born from the first mainframe database management system. It uses an upside-down tree to structure data. The top of the tree is the parent and the branches are children. Each child can only have one parent but a parent can have many children.

Advantages

• Have many different structures and forms.
• Structures data in an upside-down tree. (Simplifies data overview)
• Manages large amounts of data.
• Express the relationships between information.
• Many children per parent.
• Distribute data in terms of relationships.
• Improve data sharing.

Disadvantages

• One parent per child.
• Complex (users require physical representation of database)
• Navigation system is complex.
• Data must be organized in a hierarchical way without compromising the information.
• Lack structural independence.
• Many too many relationships not supported.
• Data independence.

NETWORK DATA MODEL

In 1965 C.W. Bachman developed the first network data model to present complex data relationships more effectively than the hierarchical model. He tried to impose a database standard with his model and also wanted to improve database performance.

It was in 1971 that the Conference on Data System Languages or CODASYL officially or formally defined the Network model. The network databases arrange its data as a directed graph and have a standard navigational language.

Advantages

• Multi-parent support.
• Somewhat same simplicity as the hierarchical model.
• More useful than the hierarchical data model.
• Deals with even larger amounts of information than the hierarchical model.
• Promotes data integrity.
• Many too many relationships support.
• Data independence.
• Improved data access.

Disadvantages

• Data relationships must be predefined.
• Much more complex than the hierarchical date model.
• Users are still require to know the physical representation of the database
• Information can be related in various and complicated ways.
• Lack structural independence.

RELATIONAL DATA MODEL

The relational data model was introduced in 1970 by Edgar F. Codd. He worked for IBM. All data is represented as simple tabular data structures which the user can access through a high-level non-procedural language. In 1974 IBM proposed a new high-level non-procedural language – SEQUEL (renamed into SQL in 1990).

Advantages

• Structured independence is promoted.
• Users do not have to know the physical representation of the database.
• Use of SQL language to access data.
• Easier database design.
• Tabular view improves simplicity.
• Support large amounts of data.
• Data independence.
• Multi-level relationships between data sets
• No need to predefined data relationships.

Disadvantages

• Data anomalies.
• People need training if they want to use the system effectively and efficiently.

ENTITY RELATIONSHIP DATA MODEL

Dr. Peter Pin-Shan Chen introduced the entity relationship data model in 1976. It is a graphical representation of entities that became popular very quickly because it complemented the relational database model concepts.

Advantages

• A very important data modeling tool.
• An extended Entity-Relationship diagram allows more details.
• Multi-valued attributes.
• Structured independence.
• Organize the data into categories defining entities & the relationships between them.
• Visual representation.
• Data independence.

Disadvantages

• Limited relationship representation.
• Loss of information (when attributes are removed from entities).
• No data manipulation language.
• Limited constraint representation.

BIOGRAPHY

• Rob, P., Coronel, C. & Crockett, K. 2008. Database systems: design, implementation & management – international edition. UK: Gaynor Redvers-Mutton. p37-51.
• Danielsen, A. The evolution of data models and approaches to persistence in database systems. 1998. Available at: http://www.fing.edu.uy/inco/grupos/csi/esp/Cursos/cursos_act/2000/DAP_DisAvDB/documentacion/OO/Evol_DataModels.html. Accessed February 15, 2010.
• Geekinterview.com. The Hierarchical Model. 2008. Available at: http://www.learn.geekinterview.com/it/data-modeling/the-hierarchical-model.html. Accessed February 15, 2010.
• Geekinterview.com. Network Model. 2008. Available at: http://www.learn.geekinterview.com/it/data-modeling/network-model.html. Accessed February 15, 2010.
• Geekinterview.com. Relational Model. 2008. Available at: http://www.learn.geekinterview.com/it/data-modeling/relational-model.html. Accessed February 15, 2010.
• Geekinterview.com. A Look at the Entity-Relationship. 2008. Available at: http://www.learn.geekinterview.com/it/data-modeling/a-look-at-the-entity-relationship.html. Accessed February 15, 2010.