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What is an entity subtype?
A subtype is a sub-grouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroups.
What is a relationship type between two entities?
A relationship is an association that exists between two entities. For example, Instructor teaches Class or Student attends Class. Most relationships can also be stated inversely.
What do you call the entity created when you resolve AM M relationship?
When you resolve a M:M by creating an intersection entity, this new entity will always inherit: Mark for Review. The attributes of both related entities.
What do you mean by weak entity?
In a relational database, a weak entity is an entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key.
What is an entity How do you identify relationships and entities?
Weak Entity Type and Identifying Relationship: As discussed before, an entity type has a key attribute which uniquely identifies each entity in the entity set. But there exists some entity type for which key attribute can’t be defined. These are called Weak Entity type.
How are relationships between subtypes of an entity represented?
All the subtypes share the most important attributes (represented on the main table) but a few of them (a minority) have aditional attributes that are represented in additional children tables. I have to represent new relationships involving rows from the main table.
How are entity subtypes related to supertypes?
An entity supertype is an entity type in which only common attributes are implemented (described) for entity subtypes that use this supertype. 3. How can entity subtypes be related together? Example Entity subtypes may or may not intersect.
Why are entity subtypes entered into the ER model?
Entity subtypes are entered into the ER model in order to reduce the total number of attributes of each entity. Each entity has a set of unique attributes. However, the attributes of different entities can be repeated.
How are nonoverlapping subtypes implemented in entity set?
Known as nonoverlapping subtypes Implementation is based on the value of the subtype discriminator attribute in the supertype Overlapping subtypes: Contain nonunique subsets of the supertype entity set Implementation requires the use of one discriminator attribute for each subtype