What are the two conditions for using Supertype subtype relationships?
Two conditions that indicate a designer should consider using supertype/subtype relationships: There are attributes that apply to some (but not all) of the instances of an entity type. The instances of a subtype participate in the relationship unique to that subtype.
What is Supertype relationships and subtype relationships?
A supertype is a generic entity type that has a relationship with one or more subtypes. 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 Supertype subtype hierarchy?
A supertype entity in one relationship may be a subtype entity in another relationship. When a structure comprises a combination of supertype/subtype relationships, that structure is called a supertype/subtype hierarchy, or generalization hierarchy.
Can a Supertype be a subtype?
A supertype can have one or more subtypes, and a subtype can have one or more supertypes. A supertype can be a subtype of some other supertype, and a subtype can be a supertype of some other subtype.
What is the purpose of a subtype discriminator?
The purpose of the subtype discriminator is to help you avoid having to write subqueries or joins just to find information such as the names of all AARP members.
What happens to the attributes of an entity type which has subtypes?
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. Details (subtleties) of each type of entity are taken out separately in several specialized subtypes.
Can a subtype have a primary key?
The subtypes will have the same primary key as their supertype.
When should a subtype be used?
Subtypes should be used when: there are attributes that apply to some but not all instances of an entity type. The process of defining one or more subtypes of a supertype and forming relationships is called: specialization.
What type of relationship is established between a supertype and an subtype?
6. What type of relationship is established between a supertype and a subtype? Between the supertype and subtype set relation “one to one” or 1:1.
What is an attribute of the supertype which is used to differentiate the subtypes?
A subtype discriminator is the attribute in the supertype entity that is used to determine to which entity subtype the supertype occurrence is related. For any given supertype occurrence, the value of the subtype discriminator will determine which subtype the supertype occurrence is related to.
What is a subtype discriminator?
A subtype discriminator is an attribute in the supertype entity that determines to which subtype the supertype occurrence is related. Disjount and overlapping constraints. Disjoint subtypes: Contain a unique subset of the supertype entity set. Each entity instance of the supertype may only exist as one of the subtypes.
When we talk of total completeness The requirement that every supertype occurrence is only part of one subtype is called?
Partial completeness means that some supertype occurrences might not be members of any subtype. Total completeness means that every supertype occurrence must be a member of at least one subtype.
Why is supertype / subtype design important in MySQL?
The important point in this kind of supertype/subtype design (also known as an exclusive arc) is to make it impossible to have rows about sedans referencing rows about semi-trucks, etc.. MySQL makes the code more verbose, because it doesn’t enforce CHECK constraints.
How are supertypes and subtypes mutually exclusive in SQL?
Exhaustive: Every instance of the supertype is also an instance of one of the subtypes. All subtypes are listed without omission. Mutually Exclusive: Each instance of a supertype is an instance of only one possible subtype.
What are some examples of supertypes and subtypes?
Supertypes and subtypes occur frequently in the real world: food order types (eat in, to go) grocery bag types (paper, plastic) payment types (check, cash, credit) You can typically associate ‘choices’ of something with supertypes and subtypes.
When do you call a group a subtype?
This may be the case when a group of instances has special properties, such as attributes or relationships that exist only for that group. In this case, the entity is called a “supertype” and each group is called a “subtype”. Subtype Characteristics A subtype:
