By Kato Mivule
Database Systems
During a database development process, often database developers will engage with their clients and users to solicit the requirements that the new database is supposed to accomplish. One of the best ways to communicate with clients and users is with the use of ER diagrams to check if the developers have fully incorporated all the requirements in the design as dictated by the client.
The ER diagrams become easy to study, visualize, and amend during the requirements soliciting process with the client. Therefore, ER diagrams are conceptional and abstract presentation of the database, fully giving a formal description of database components such as schema, entities, relationships, and attributes. [1] [2]
At the same time the Relational Model which was first introduced in 1969 by E.F Codd, is a conceptual view of a database based on first-order predicate logic, depicting a database as a set of predicate variants. The model stipulates a declaratory way for defining data and queries by requiring users to straightaway state what data they need to get from the data and place into the database.[4] Relational Models represent data as a collection of relations, depicting the database as a schema, the table as a relation, the columns as attributes, and rows as tuples.[2]
The Relational Model is declarative and therefore easy to implement using declarative languages like SQL, making it a major difference between ER Diagrams and the Relational Model. ER diagrams tend to be highly conceptual and though could be easily understood by clients and users who are not experts in database terminology, ER diagrams are not declarative and straight forward when it comes to implementation. It is therefore important to have the Relational Model interface between the ER diagrams and the SQL declarative language so as to make implementation faster and easier.
Secondly, any errors that come up during the design phase with the ER diagrams, can be captured when mapping to the Relational Model. Yet even more, wile both the ER and the Relational Model are mathematical, we can still map ER diagrams to the Relational Model, thus making implementation of the conceptual view to physical view much easier.
Yet still, the ease of use between the ER Model and Relational Model is still debatable. Peter P. Chen, the author of the ER model in the 1970s notes three differences between the ER Model and E.F. Codd’s Relational Model: [6] [7]
- ER models employ mathematical relation constructs to show relationships between entities…
- ER model incorporates more semantic data than the Relational Model…
- ER model uses explicit linkage between entities while the Relational model uses implicit linkages between entities…
Yet still despite the advantages of more semantic information with the Chen’s ER model, Codd’s Relational model is closer to SQL implementation and has the declarative advantage. Therefore, for the conceptual view, the ER diagram work best but will work better when mapped to the Relational model for optimized physical view implementation.
Sources
[1] Seyed M. M. Tahaghoghi, Hugh E. Williams, “Learning MySQL”, O’Reilly Media, Inc., 2006, ISBN 0596008643, 9780596008642, Page 112-118
[2] Ramez Elmasri, Shamkant B. Navathe, Fundamentals of Database Systems, Edition 6, Addison Wesley Pub Co Inc, 2010, ISBN 0136086209, 9780136086208, Page 199-350
[3] Heidi Gregersen and Leo Mark and Christian S. Jensen, “Mapping Temporal ER Diagrams to Relational Schemas”, IN PROC. OF THE 9TH INT. CONF, 1998.
[4] “Relational model – Wikipedia, the free encyclopedia.” [Online]. Available: http://en.wikipedia.org/wiki/Relational_model. [Accessed: 02-Nov-2010].
[5] “Entity-relationship model – Wikipedia, the free encyclopedia.” [Online]. Available: http://en.wikipedia.org/wiki/Entity-relationship_model. [Accessed: 02-Nov-2010].
[6] Peter Chen, “Entity-Relationship Modeling: Historical Events, Future Trends, and Lessons Learned”, Software Pioneers: Contributions to Software Engineering, Springer, 2002.
[7] E.F. Codd, “A relational model of data for large shared data banks. 1970.,” M.D. computing : computers in medical practice, vol. 15, 1970, pp. 162-6.
