Week 12 UAS

Question 1

The concept of specialization/generalization is associated with special types of entities known as?

Answer 1

1. Superclass: An entity type that includes one or more distinct subgroupings of its occurrences.
2. Subclass: A distinct subgrouping of occurrences of an entity type.

Question 2

What is specialization?

Answer 2

Process of maximizing differences between members of an entity by identifying their distinguishing characteristics.

Question 3

What is Generalization?

Answer 3

Process of minimizing differences between entities by identifying their common characteristics.

Question 4

4 categories of constraints of specialization and generalization?

Answer 4

1. mandatory and disjoint
2. optional and disjoint
3. mandatory and nondisjoint
4. optional and nondisjoint.

Question 5

two constraints that apply to a specialization/generalization?

Answer 5

1. participation constraints
Determines whether every member in superclass must participate as a member of a subclass.

2. disjoint constraints
Describes relationship between members of the subclasses and indicates whether member of a superclass can be a member of one, or more than one, subclass.

Question 6

Concepts of the ER Model?

Answer 6

1. Entity types
   Group of objects with same properties, identified by enterprise as having an independent existence.
2. Relationship types
   Set of meaningful associations among entity types.
3. Attributes
   Property of an entity or a relationship type.

Question 7

Attributes can be classified as being?

Answer 7

1. Simple Attribute
   Attribute composed of a single component with an independent existence.
2. Composite Attribute
   Attribute composed of multiple components, each with an independent existence.
3. Single-valued Attribute
   Attribute that holds a single value for each occurrence of an entity type.
4. Multi-valued Attribute
   Attribute that holds multiple values for each occurrence of an entity type.
5. Derived Attribute
   Attribute that represents a value that is derivable from value of a related attribute, or set of attributes, not necessarily in the same entity type.

Question 8

Keys?

Answer 8

1. Candidate Key
   Minimal set of attributes that uniquely identifies each occurrence of an entity type.
2. Primary Key
   Candidate key selected to uniquely identify each occurrence of an entity type.
3. Composite Key
   A candidate key that consists of two or
   more attributes.

Question 9

Entity Type?

Answer 9

1. Strong Entity Type
   Entity type that is not existence- dependent on some other entity type.
2. Weak Entity Type
   Entity type that is existence- dependent on some other entity type.

Question 10

What is Multiplicity?

Answer 10

the number (or range) of possible occurrences of an entity type that may relate to a single occurrence of an associated entity type through a particular relationship.

Multiplicity is made up of two types of restrictions on relationships: cardinality and participation.
1. Cardinality
Describes maximum number of possible relationship occurrences for an entity participating in a given relationship type.
2. Participation
Determines whether all or only some entity occurrences participate in a relationship.

Question 11

Problems with ER Models?

Answer 11

1. Fan Trap
   Where a model represents a relationship between entity types, but pathway between certain entity occurrences is ambiguous.
2. Chasm Trap
   Where a model suggests the existence of a relationship between entity types, but pathway does not exist between certain entity occurrences.