Enhanced E-R Model
type that has attributes distinct from those in other subgroupings! Supertype: A generic entity type that has a relationship with one or more subtypes! Attribute. A supertype is a generic entity type that has a relationship with one or more A subtype is a sub-grouping of the entities in an entity type that is meaningful to the . subtypes which are connected to a specific supertype will have all the The Figure:1 above shows that the supertype and subtype relation between the.
Select Inclusive or Exclusive subtype. Select if each supertype that has subtypes can be more than one subtype at a time.
Select if each supertype that has subtypes can be only one subtype at a time. In IE notation, an exclusive subtype is represented with an exclusive OR symbol. Select a discriminator from the list.
A discriminator is an attribute that distinguishes each of the subtype entities from one another. A subtype discriminator can be a primary key or non-key attribute of the supertype.
Creating Subtype Cluster Relationships - ER/Studio Data Architect
Attachment Bindings tab Bind an external piece of information, or attachment to the domain. You can also remove an attachment from an object, override an attachment binding's default value, or change the position of a bound attachment.
To override the value of the attachment you have moved to the Selected Attachments grid, double-click the Value field of the target attachment.
Attachments are created in the Attachments folder of the Data Dictionary. You can edit the subtype by right-clicking the subtype cluster symbol and then selecting Edit Subtype Cluster. You can change the colors of the subtype cluster symbol, by right-clicking it and then selecting Subtype Cluster Color.
Use this approach if an occurrence of a Subtype participates in a relationship. The Total Specialization Rule specifies that this is the case. This is diagrammed with a double line from the Supertype to the circle as shown here.
- Database Management Systems
- Tables for Supertype and Subtype Entities in Oracle Communications Data Model
The Partial Specialization Rule is the one we have followed thus far in the notes single line to the circle -- no such constraint exists. This type of business rule deals with the situation where an occurrence of a Supertype may also have more than one Subtype occurrence.
The Disjoint Rule says that this cannot occur. The Overlap Rule says that this can happen.
This means that a Ford 8-cylinder Mustang engine could either be manufactured at the factory or purchased from a vendor, but it would still be a Ford 8-cylinder Mustang engine! The subtypes are usually but may not be mutually exclusive with no overlap. This is diagrammed by placing either the letter "d" or "o" inside the circle on the Generalization Hierarchy portion of the E-R diagram. A Subtype Discriminator is an attribute of the Supertype that is used to "code" or denote which Subtype an entity is.
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This attribute may enhance system performance during program coding of maintenance programs for the database tables during the physical design phase of a project.
While your text discusses various ways to use Subtype Discriminators for Disjoint or Overlapping subtypes, coding of the attribute in the Supertype will handle all possibilities. It is possible for a Subtype entity to be a Supertype entity in another relationship. This creates a hierarchy of Supertypes and Subtypes.