DBMS Chapter 8 Flashcards
Enhanced-ER (EER) Model Concepts
Includes all concepts of ERD
plus sub/superclasses, specialization/generalization,
attribute inheritance, categories
subclass
An entity that inherits all attributes of the entity as a member of the superclass It also inherits all relationships
Superclass
entity type that may have additional subgroupings
Specialization
Is the process of defining a set of subclasses of a superclass
Generalization
generilizing common features in several classes EX: vehicle is a superclass to car and truck
3 Constraints on Specialization and Generalization
predicate-defined (or condition-defined) subclasses
attribute defined-specialization
user-defined specialization
Disjointness Constraint:
This means that an entity can be a member of at most one of the subclasses of the specialization. If not disjointed they overlap; signified with a d or an o
Completeness Constraint
Total specifies that every entity in the superclass must be a member of some subclass in the specialization/ generalization. signified with double line == Partial allows an entity not to belong to any of the subclasses signified with single line ---
what is the requirement. to determine if entities are condition-defined subclasses?
If we can determine exactly those entities that will become members of each subclass by a condition
what is the requirement. to determine if entities are attribute-defined subclasses?
If all subclasses in a specialization have membership condition on same attribute of the superclass
what is the requirement. to determine if entities are user-defined subclasses?
If no condition determines membership
Hierarchy specialization
Hierarchy has a constraint that every subclass has only one superclass. Creates tree structure
Lattice Specialization
a subclass can be subclass of more than one superclass (called multiple inheritance). Creates a diamond structure
Union Type use:
to model a single superclass/subclass relationship with more than one superclass : denoted with horseshoe and U Example: owner of a car(person, bank, company)