HOPEX Data Governance > Data Architecture and Tools > Modeling Data dictionaries > I.E. Notation > Sub-types (I.E)
Sub-types (I.E)
*A generalization represents an inheritance relationship between a general entity and a more specific entity. The specific entity is fully consistent with the general entity and inherits its characteristics and behavior. It can however include additional attributes or associations. Any object of the specific entity is also a component of the general entity.
What is sub-type? 
An entity B is a subtype of entity A. This assumes that all instances of entity B are also instances of entity A. In other words, B is a subset of A. B is then the subtype, and A the supertype.
Example:
A: Person, B: Bostonian.
B being a subset of A, the instances of entity B "inherit" the characteristics of those in entity A.
It is therefore unnecessary to redescribe for entity B:
• Its attributes
• Its associations
Example:
The "Large Client" entity, representing clients with a 12-month revenue exceeding $1 million, can be a subtype of the Client entity.
A subtype inherits all attributes, associations, roles and constraints of its supertype, but it can also have attributes, associations, roles or constraints that its supertype does not have.
In the above example, the attributes, associations, roles and constraints specified for "Client" are also valid for "Large Client".
Multiple Subtypes 
Several subtypes of the same entity:
• are not necessarily exclusive.
• do not necessarily partition the type.
Advantages of sub-types 
A subtype entity inherits all the attributes and associations of its supertype entity, but can have attributes or associations that the supertype entity does not have.
A subtype entity can also have specific attributes. These only have meaning for that particular sub-entity. In the above example:
• "Registry number" and "number of employees" only have meaning for a "company".
• "Date of birth" is a characteristic of a "person", not a "company".
A subtype entity can also have specific associations.
• A "person" falls into a "socio-professional group": "manager", "employee", "shopkeeper", "grower", etc. This classification makes no sense for a "company". There is also a classification for companies, but it differs from that for persons.
Multiple inheritance 
It is sometimes useful to specify that an entity has several supertypes. The subtype inherits all the characteristics of both supertypes. This possibility should be used carefully.
Creating a sub-type 
To create a subtype:
1. Click the Generalization button in the objects toolbar.
2. Click the subtype entity, drag the mouse to the supertype entity, then release the button.
The generalization is now pictured in the diagram by an underlined semicircle connected by a line to the supertype entity and by another line to the subtype entity.
In the above example, attributes are interesting on persons that are of no avail for other categories of clients. The subtype entity is represented by a rounded corner box.