D426 Database Design / SuperType Subtype

optional /required

a related entity is optional when the minimum is zero and required when the minimum is one

Attribute maximum

the greatest number of attrbitute values that can describe each entity instance. attribute maxium is specified as one (singular) or many (plural)

Attribute minimum

the least number of attribute values that can describe each entity instance. is specified as zero (optional) or one (required)

Unique attribute

each value of a unique attribute describes at most one entity instance

Identifying attribute

unique singular and required

Identify

identifying attribute values correspond one-to-one or identify entity instances

Strong entity

a strong entity has one or more identifying attributes

weak entity/ identifying relationship / identifying entity

a weak entity does not have an identifying attribute but has relationship called identifying relationship to another entity called identifying entitity.

Identifying entity must be singular and required in an identifying relationship

Subtype

subset of another entity

Similar entity

have many common attributes and relationship with entities

Partition

partition supertype entity is a group of mutually exclusive subtype entities

Partition attribute

each partition corresponds to an optional partition attribute of supertype entity

IsA relationship

a supertype entity identifies its subtype entities. the identfying relationship is called an IsA relationship