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Data Management Concepts > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

What is an entity?

A
  • Entity instance - person, place, object, event, concept (often corresponds to a row in a table)
  • Entity type - collection of entitities (often corresponds to a table)
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2
Q

What are relationships?

A

Relationship instance - link between entities (corresponds to primary key-foreign key equivaltencies in related tables)

Relationsihp type - category of relationship.. link between entity types

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3
Q

What are attributes?

A

Properties or characteristics of an entity or relationship type (often corresponds to a field in a table)

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4
Q

Sample E-R Diagram

A
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5
Q

Basic E-R notation (visualized)

A
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6
Q

What are business rules?

A

Statements that define or constrain some aspect of the business.

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7
Q

What are business rules derived from?

A

Policies, procedures, events, and functions

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8
Q

What are some aspects of business rules?

A
  • Assert business structure
  • Control/influence business behavior
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9
Q

How are business rules expressed/automated?

A
  • They are expressed in terms that are familiar to end users
  • Automated through DBMS software
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10
Q

What are the components of a good business rule?

A
  • Declarative
  • Precise
  • Atomic
  • Consistent
  • Expressable
  • Distinct
  • Business-oriented
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11
Q

Business Rules - What does declarative mean?

A

What, not how

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12
Q

Business Rules - What does precise mean?

A

Clear, agreed-upon meaning

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13
Q

Business rules - What does atomic mean?

A

One statement

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14
Q

Business rules - What does consistent mean?

A

internally and externally consistent

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15
Q

Business Rules - What does expressible mean?

A

Structured, natural language

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16
Q

Business Rules - What does distinct mean?

A

non-redundant

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17
Q

Business Rules - What does business-oriented mean?

A

Understood by business people

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18
Q

What are the components of a good data name?

A
  • Related to business, not technical, characteristics
  • Meaningful and self-documenting
  • Unique
  • Readable
  • Composed of words from an approved list
  • Repeatable
  • Written in standard syntax
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19
Q

What is a data definition?

A

Explanation of a term or fact

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20
Q

What is a term?

A

word or phrase with specific meaning

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21
Q

What is a fact?

A

association between two or more terms

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22
Q

What are the guidelines for good data definition?

A
  • Concise description of essential data meaning
  • Gathered in conjunction with systems requirements
  • Accompanied by diagrams
  • Achieved by consensus, and iteratively refined
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23
Q

What is an entity?

A

a person, place, object, event, or concept in the user environment about which the organization wishes to maintain data

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24
Q

What is an entity type?

A

A collection of entities that share common properties or characteristics.

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25
Q

What is an entity instance?

A

A single occurrence of an entity type

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26
Q

Entity type/instance example

A
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27
Q

What should be an entity?

A
  • An object that will have many instances in the database
  • An object that will be composed of multiple attributes
  • An object that we are trying to model
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28
Q

What should an entity not be?

A
  • A user of the database system
  • An output of the database system (e.g. a report)
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29
Q

Example of Appropriate/Innappropriate entities

A
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30
Q

What are characteristics of a strong entity?

A
  • Exists independently of other types of entities
  • Has it’s own unique identifier (identifiter underline with single line)
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31
Q

What are the characteristics of a weak entity?

A
  • Dependent on a strong entity (identifying owner), cannot exists on its own
  • Does not have a unique identifier (only a partial identifier)
  • Entity box and partial identifier have double lines
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32
Q

What is an identifying relationship in relation to entities?

A
  • Links strong entities to weak entities
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33
Q

Stong vs. Weak entity visualized

A
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34
Q

What are the guidelines for naming entities?

A
  • Singular Noun
  • Specific to organization
  • Concise, or abbreviation
  • For event entities, the result not the process
  • Name consistent for all diagrams
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35
Q

What are the guidelines for defining entities?

A
  • “an X is”
  • Describe unique characteristics of each instance
  • Explicit about what is and is not the entity
  • When an instance is created or destroyed
  • Changes to other entity types
  • History that should be kept
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36
Q

What is an attribute?

A

Property or characteristic of an entity or relationship type

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37
Q

What are the classifications of attributes?

A
  • Required vs Optional
  • Simple vs Composite
  • Single-valued vs Multivalued
  • Stored vs Derived
  • Identifier
38
Q

Example of Required vs Optional Attributes

A
39
Q

What is a required attribute?

A

Must have a value for every entitiy (or relationship) instance with which it is associated

40
Q

What is an optional attribute?

A

May not have a value for every entity (or relationship) instance with which it is associated.

41
Q

What is a composite attribute?

A

An attribute that has meaningful component parts (attributes)

42
Q

Composite attribute (example)

A
43
Q

What is a multivalued attribute?

A

May take on more than one value for a given entity (or relationship) instance

44
Q

What is a derived attribute?

A

Values can be calculated from related attribute values (not physically stored in the database)

45
Q

Multivalued and Derived attribute example

A
46
Q

What is an identifier (Key)?

A

An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type

47
Q

What are the two types of identifiers?

A
  • Simple
  • Composite
48
Q

What is a candidate identifier?

A

An attribute that could be an identifier (satisfies the requirements for being an identifier)

49
Q

What are two criteria for choosing identifiers?

A
  • Will not change in value
  • Will not be null
50
Q

What should you avoid in identifiers?

A
  • Intelligent identifiers (containing locations or people that might changed, basically information that might change)
51
Q

What should you do for long composite keys?

A

Substitute new simple keys

52
Q

Simple and Composite Identifier example

A
53
Q

What requirements are there when naming attributes?

A
  • Name should be a singular noun or noun phrase
  • Name should be unique
  • Name should follow a standard format
  • Similar attributes of different entity types should use the same qualifiers and classes
54
Q

What are the requirements when defining attributes?

A
  • State what the attribute is and possibly why it is important
  • Make it clear what is and is not included in the attribute’s value
  • Include aliases in documentation
  • State source of values
  • State whether attribute value can change once set
  • Specify required vs. optional
  • State min and max number of occurences allowed
  • Indicate relationships with other attributes
55
Q

What is the difference between relationship types and relationship instances?

A
  • Relationship type is modeled as lines between entity types
  • Relationship Instance is between specific entity instances
56
Q

What is the difference between relationship types and relationship instances?

A
  • Relationship types are modeled as lines between specific entity types
  • Relationship instances are between specific entity instances
57
Q

Can relationships have attributes?

A
  • Yes, these describe features pertaining to the associations between the entities in the relationship.
58
Q

Can entities have more than one relationship between them?

A
  • Yes, these are call multiple relationships
59
Q

What is an associative entity?

A

Combination of relationship and entity

60
Q

Relationship types and instance visualized

A
61
Q
A
62
Q

What is the degree of a relationship?

A

The number of entity types that participate in it

63
Q

What are the three types of relationships?

A
  • Unary
  • Binary
  • Ternary
64
Q

Relationship degrees visualized

A
65
Q

What are the cardinality of relationships?

A
  • One-to-one
  • One-to-many
  • Many-to-Many
66
Q

What is a one-to-one relationship cardinality?

A

Each entity in the relationship will have exactly one related entity

67
Q

What is a one-to-many relationship cardinality?

A
  • An entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity
68
Q

What is a many-to-many relationship cardinality?

A

Entities on both sides of the relationship can have many related entities on the other side

69
Q

Unary relationship examples

A
70
Q

Binary relationship example

A
71
Q

Ternary relationship example

A
72
Q

What are cardinality Constraints?

A

The number of instances of one entity that can or must be associated with each instance of another entity.

73
Q

What are the minimum cardinalities?

A
  • If zero, then optional
  • If one or more, then mandatory
74
Q
A
75
Q

What is the maximum cardianality?

A

The maximum number

76
Q

Example of cardinality constraints

A
77
Q

Examples of cardinality constraints, optional and mandatory

A
78
Q

Examples of cardinality constraints, all optional

A
79
Q

Examples of mulitple relationships

A
80
Q

Example of multiple relationships, fixed lower limit constraint

A
81
Q

Simple and Composite attributes shown as relationships

A
82
Q

What does an entity have?

A

Attributes

83
Q

What does a relationship do?

A

Links Entities together

84
Q

When should a relationship with attributes instead be an associative entity?

A
  • When all relationships for the associative entity should be many
  • When the associative entity could have meaning independent of the other entitiies
  • When the associative entity preferably has a unique identifier, and should also have other attributes
  • The associative entity may participate in other relationships other than th entities of the associated relationship
  • Ternary relationships should be converted to associative entities
85
Q

Binary relationship with an attribute example

A
86
Q

What is an associative entity similar to?

A

A relationship with an attribute.

87
Q

Associative entity example

A
88
Q

Good example of ternary relationship and business rules

A
89
Q

What is a time stamp?

A

a time value that is associated with a data value, often indicating when some event occured that affected the data value

90
Q
A

Data Management Concepts (12 decks)

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