For information management (IM) professionals, entity relationship modelling has become a necessary skill set.
Our current challenge is to build information governance tools – classification schemes, retention schedules etc. – which fit into a variety of information architectures. And this is where entity relationship modelling is useful.
An entity relationship model (or diagram) is a conceptual data model that represents structured data in terms of entities, attributes and relationships.
An entity is something that exists in itself, actually or hypothetically and can be uniquely identified. Entities can be thought of as nouns. Common entities in IM are terms, document types, contacts, organizations, repositories, systems.
Attributes are characteristics or particular properties that describes the entity, also known as the metadata describing the entity. Attributes can be many and varied and include names, dates, descriptions, etc.
Relationships are the interactions between the entities. Relationships can be thought of as verbs, linking two or more entities. Common relationships in IM are broader than, narrower than, use, use for.
Cardinality defines the relationship between the entities in terms of numbers. The main cardinal relationships are: one-to-one, one-to-many, and many-to-many.
The entity-relationship diagram (ERD) is used to represent information objects and their relationships visually.
Notation provides the means to represent these building blocks are represented in a standardise format. In Crow’s Foot notation entities are presented as boxes, and relationships as lines between the boxes. Cardinality is represented by different ends to each line.
So a Thesaurus is represented like this:
And the Term entity can be represented like this:
Simple isn’t it. There is, of course, an entire branch of information science devoted to database design and entity relationship modelling, but more about that in future posts.
My point is that models and diagrams are important tools as they are easy to understand and help bridge the gap between management, information managers and system / database developers.
There are a bunch of tools available to assist with building entity relationship diagrams. After playing with many, I have settled on Gliffy – an online business graphics application.
In another post we will look at the concept of the Conceptual Data Model and how this can be used to develop an information governance framework.