Information Management - 4 Flashcards

1
Q

Entity Relationship Model

A
  • ER model is the basis of ER diagrm
  • represents conceptual database viweed as endsuer
  • Composed of: entities, relationship, attribute
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2
Q

Entities

A
  • refers to entity and not a single entity
  • Corresponds to table and not row in relational environment
  • In Chen and Crow’s diagram, entity name is writtten inside the rectangle
  • Entity is noun with capital lettters
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3
Q

Attribute

A

characteristics of an entity

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4
Q

Chen notation

A

attribute is written in an oval conncted to entity

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5
Q

Crow’s foot

A

attribute is within the attribute box below any rectangle

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6
Q

Required attribute

A

must have a value

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7
Q

Optional Attribute

A

may be left null

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8
Q

Composite Identifier

A

primary key composed of one or more attribute

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9
Q

Identifiers

A

one or more attributes that uniquely identify each entity instance

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10
Q

Composite attribute

A

can be subdivided

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11
Q

Simple attribute

A

cannot be subdivided

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12
Q

Single-value attribute

A

can only have a single value

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13
Q

Multivalued attribute

A

can have multiple values

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14
Q

Derived Attribute

A

can be calculated from other attribute

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14
Q

Relationship

A
  • Association between entities
  • Participants are entities that participate in a relationship
  • Relationships between entities always operate in both directions
  • Relationship can be classified as 1:M
  • Relationship classification is difficult to establish if only one side of the relationship is known
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15
Q

Connectivity

A

relationship classification

16
Q

Cardinality

A

minimum and maximum number of entitiy occurance

17
Q

existence dependence

A

Entity exists in database only when it is associated with another related entity occurrence

18
Q

Existence Indepencence

A
  • entity can exist apart from one or more related entities
  • sometimes known as strong entities
19
Q

Weak Relationship

A

Exists if PK of related entity does not contain PK component of parent entity

20
Q

Strong Relationship

A

Exists when PK of related entity contains PK component of parent entity

21
Q

Weak Entity

A
  • existence-dependence
  • primary key came from parent key
22
Q

Optional Participation

A

One entity occurrence does not require corresponding entity occurrence in particular relationship

23
Q

Mandatory Participation

A

One entity occurrence requires corresponding entity occurrence in particular relationship

24
Q

Relationship Degree

A

indicates the number of entities and participants associated with the relationship

  • Unary Relationship - associated with a single entitity
  • Binary Relationship - associated with two entities
  • Ternary Relationship -associated with three entities
25
Q

Recursive Relationship

A

Relationship can exist between occurrences of the same entity set

26
Q

Assiciative (Compostite) Entity

A
  • bridge the entities
  • Implement M:N relationship
  • Composed of pk of each entities
  • may also contain additional attributes
27
Q

UML class diagrams

A

used to represent static data structures in data model