Using a representative graphical entity-relationship model describe the purpose and notation of this model using a simple example; and explain why the ER-model improves the definition of user requirements.

CPA-Quantitative-Analysis-Section-4 BLOCK RELEASE

Entity relationship model

Any representative graphical model is acceptable as an answer to this part of the question. This sample answer concerns the entity-relationship model.
i) The entity-relationship model describes the main ―things‖ of interest to the business and defines the relationships between them. It provides a graphical representation of some of the business rules of the system and these need to be confirmed the user. For example, an entity type CLAIM may be in a one-to- many relationship with another entity type PAYMENT. This will have to be confirmed with a representative business user ñ can they confirm that an individual payment is never for more than one claim? The entity-relationship model also forms a basis for subsequent file and database design.

In an entity-relationship model, rectangular boxes show the main entity types (entities) of the system. Entities are defined as singular nouns that describe important business objects, events or concepts. The lines between the entities define relationships. These are usually one-to-one , one-to-many, or many-to-many. The many end of a relationship is shown as a ―crow‘s foot‖.

The relationship is made more precise if the minimum and maximum values are specified on the relationship, as shown in the following example, using the Martin/Odell notation.
For example, in the relationship between PAYMENT and CLAIM, a CLAIM may be associated with a minimum of zero payments (because the CLAIM is rejected) and a maximum of many. A PAYMENT is for a minimum of one CLAIM and also a maximum of one CLAIM.
ii) The model is an improvement on textual specification in at least two ways.
Firstly, it is a more compact way of showing the business rules and specifying these in consistent detail. Secondly, it also identifies what business relationships are not supported. For example, in the above entity-relationship model there is no direct link (or relationship) between CLAIM and PAYMENT TYPE. This means there is no direct business relationship between a particular CLAIM and the way it is settled. It is very unlikely that this unsupported business rule would be explicitly stated in a

Textual specification.

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