Karteikarten
Databases Chapter 4
Karten in diesem Stapel (19)
- 1What does EER stand for?Enhanced Entity Relationship
- 2Why were EER diagrams created?- to design a more accurate database schema
- Reflect data properties and constraints more precisely - 3What is the notion of Subclasses and and Superclassesan entity may have additional meaningful sub groupings of its entities
- 4What subgroupings of EMPLOYEE?Subclasses:
Secretary
Technician
Manager - 5What would EMPLOYEE be considered as?Superclass
- 6What is the relationship from a superclass to its subclasses called?"IS-A" relationships
- 7What does an entity of that is a member of a subclass inherit?All attributes and all relationships of the entity as a member of the superclass
- 8What is Specialization?Specialization is the process of defining a set of subclasses of a superclass
- 9Name the reasons why one would include class/subclass relationships and specialization in a data model-certain attributes may apply to some but not all entities of the superclass
- Some relationship types may be participated in only by members of the subclass - 10What is generalization?Generalization is the reverse of the specialization process
- Several classes with common features and generalized into superclass - 11Describe the specialization type, Predicate-defined(condition defined): Based on some predicate. E.g., based on value of an attribute, say Job-type, or Age
- 12Describe the specialization type, Attribute-definedShows the name of the attribute next to the line drawn from the superclass toward the subclasses
- 13Describe the specialization type, User-definedmemnbership is defined by the user on an entity by entity basis
- 14What are the 2 basic constraints that can be applied to Specialization and Generalization?Disjointness Constraint
Completeness Constraint - 15Describe the disjointness constraintSpecifies that the subclasses of the specialization must be disjoint.
- an entity can be a member of at most one of the subclasses of the specialization
- (d)
-if not disjoint, the specialization is overlapping
- the same entity may be a member of more than one subclass of the specialization
- (o) - 16Describe the Completeness constraint-Total specifies that every entity in the supercall must be a member of some subclass in the specialization/generalization
-shown in diagram by double lines
-Partial allows an entity not to belong to any of the subclasses - 17What are the 4 types of generalization/specializations?-Disjoint, total
-Disjoint, Partial
-Overlapping, total
-Overlapping, partial - 18What is the constraint of a Hierarchy?That every subclass has only one superclass (called single inheritance); this is basically a tree structure
- 19Describe what a lattice isa subclass can be subclass of more than one superclass (multiple inheritance) (shared subclasses)