Model Requirement – Entity Relationship Diagram

In the previous posts, we were already familiar with Permission Matrix. This week, I’d like to write about another kind of Stakeholder Requirement – Entity Relationship Diagram – which shows relationships between Actors and Objects within the system.

To draw this diagram, recall that we mention to Data Modelling technique. This diagram is Logical Data Model with 3 main components: Entity/Class, Attribute, Relationship/Association.Screen Shot 2017-05-20 at 11.09.43 PM

(IIBA. 2015. BABOK. [Image])

  • Entity/ Class (also mentioned as Property in UML): in general, they are Actors and Objects in the system. We can use color code to differentiate Actor and Object, or group similar objects for easier drawing. Entity should be singular noun.
  • Attribute: defines a particular piece of information associated with an entity, including Name, Value/Meaning, Description, Visibility, Default Value, Multiplicity, etc. Only Name is mandatory, while the others are optional. Hence, in case Name of each entity is unique, this Attribute can be skipped to simplify the diagram. It’s also the reason why most of the time, with not-so-complicated-system, we don’t see Attribute in the Entity Relationship Diagram.
  • Relationship/Association: indicates which entities relate to which others and how. It’s a solid line between two entities, with multiplicity/ cardinality at each side like 1 and 0 as you can see in the image above. However, this multiplicity is also optional, and sometimes is skipped with the purpose of simplifying the diagram. Relationship should be a verb (phrase).

If we skip Attribute and multiplicity in Relationship, we can have a quite simple Entity Relationship Diagram as below:

Picture1

Thanks for reading 🙂

Reference:

  1. IIBA. 2015. BABOK. Version 3.0.
  2. Martin Fowler. 2003. UML Distilled. 3rd ed.
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