Data models

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HIERARCHICAL DATA 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

Disadvantages

Have many different structures and forms.

One parent per child.

Structures data in an upside-down tree. (Simplifies data overview)

Complex (users require physical representation of database)

Manages large amounts of data.

Navigation system is complex.

Express the relationships between information.

Data must be organized in a hierarchical way without compromising the information.

Many children per parent.

Lack structural independence.

Distribute data in terms of relationships.

Many too many relationships not supported.

Improve data sharing.

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.

In 1971 the Conference on Data System Languages (CODASYL) officially defined the Network model. The network databases arrange its data as a directed graph and have a standard navigational language.

Advantages

Disadvantages

Multi-parent support.

Data relationships must be predefined.

Somewhat same simplicity as the hierarchical model.

Much more complex than the hierarchical date model.

More useful than the hierarchical data model.

Users are still require to know the physical representation of the database

Deals with even larger amounts of information than the hierarchical model.

Information can be related in various and complicated ways.

Promotes data integrity.

Lack structural independence.

Many too many relationships support.

Data independence.

Improved data access.

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

Disadvantages

Structured independence is promoted.

Data anomalies.

Users do not have to know the physical representation of the database.

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

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.

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

Disadvantages

A very important data modeling tool.

Limited relationship representation.

An extended Entity-Relationship diagram allows more details.

Loss of information (when attributes are removed from entities).

Multi-valued attributes.

No data manipulation language.

Structured independence.

Limited constraint representation.

Organize the data into categories defining entities & the relationships between them.

Visual representation.

Data independence.

BIOGRAPHY

Rob, P., Coronel, C. & Crockett, K. 2008. Database systems: design, implementation & management - international edition. UK: Gaynor Redvers-Mutton. pp37-51.

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.

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