The Hierarchical Model

The Hierarchical ModelWas developed in the 1960s. The Hierarchical model was essentially born from the first mainframe infobase management system. It uses an upside-down tree to expression info. The top of the tree is the parent and the branches are children. Each child chamberpot only have one parent but a parent preempt have many children.AdvantagesHave many different structures and forms.Structures data in an upside-down tree. (Simplifies data overview)Manages large amounts of data.Express the familys between information.Many children per parent.Distribute data in terms of relationships.Improve data sharing.DisadvantagesOne parent per child.Complex (users acquire physical representation of database)Navigation system is complex.Data must be organized in a hierarchical way without compromising the information.Lack structural independence.Many to a fault many relationships not supported.Data independence.NETWORK data poseurIn 1965 C.W. Bachman developed the first network da ta model to present complex data relationships more effectively than the hierarchical model. He try 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.AdvantagesMulti-parent support. middling 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.DisadvantagesData relationships must be predefined.Much more complex than the hierarchical date model.Users are still require to know the physical representation of the databaseInformation can be related in various and complicated ways.Lack structural independence.RELATIONAL DATA MODELThe 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).AdvantagesStructured 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 setsNo need to predefined data relationships.DisadvantagesData anomalies.People need training if they want to use the system effectively and efficiently.ENTITY RELATIONSHIP DATA MODELDr. Peter Pin-Shan subgenus 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 relatio nal database model concepts.AdvantagesA very big 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.DisadvantagesLimited relationship representation.Loss of information (when attributes are removed from entities).No data manipulation language.Limited constraint representation.BIOGRAPHYRob, 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.