Chapter 4: Principles of Conceptual Database Design

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Part II Database Analysis

• Determine User Requirements
• Develop Data Models
• A conceptual data model is one that represents
  data from the viewpoint of the user, independent
  of any technology that will be used to implement
  the model.
• ?

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Chapter 3 Modeling Data in the Organization
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Reality and Models
Reality
Mapping
Model
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The Importance of Data Modeling

• Characteristics captured during data modeling
• crucial in design of databases, programs, other
  items
• facts and rules essential in assuring data
  integrity
• Data rather than processes are the most complex
  aspects of the modern organization
• Data tend to be more stable than the business
  processes that use the data
• ?

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Business Rules

• A business rule
• is a statement that defines or constrains some
  aspect of the business.
• It is intended to assert business structure or
  to control or influence the behavior of business
  
• Rules prevent, cause, or suggest things to
  happen.
• Business rules
• Guide behavior
• Expressible and understandable by users
• Maintainable
• Enforcement can be automated
• ?

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Data Names and Definitions

• Names
• Relate to business
• Be meaningful
• Be unique
• Readable
• Approved list
• Repeatable

• Definitions
• Same source as sys. req.
• Accompany by diagrams
• State characteristics
• Subtleties
• Special conditions
• Examples
• Where, when, how
• Static or dynamic
• Singular or plural
• Who determines value
• Who owns it
• Optional, null
• Atomic, composite

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Entities

• Person, place, object, event, or concept
• in the user environment
• about which the organization wishes to maintain
  data
• Entity type
• collection of entities that share common
  properties or characteristics
• CAPITAL LETTERS, singular
• Entity instance
• single occurrence of an entity type
• ?

ENTITY
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Entities

• Entities are not
• system input, system output, or users
• a true data entity will have many possible
  instances
• Strong or weak?
• strong entity type exists independently of other
  entity types
• weak entity type is an entity type whose
  existence depends on some other entity type
• ?

Identifyingrelationship
STRONG ENTITY
WEAK ENTITY
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Entity Names and Definitions

• Names
• Singular noun
• Specific to organization
• Concise
• Abbreviation or short name should be specified
• Result of event, not process of event
• Consistent on all diagrams

• Definitions
• An X is
• Included and excluded
• Creation and deletion
• Change
• History to be kept

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Attributes

• Property or characteristic of an entity type that
  is of interest to the organization
• initial capital letter followed by lowercase
  letters
• underscore instead of space
• Simple or Composite?
• composite has component parts
• will users need to refer to those individual
  components?
• Single-valued or Multivalued?
• Stored or Derived?
• ?

Name
Number
PLAYER
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Identifier Attribute

• An identifier is an attribute (or combination of
  attributes) that uniquely identifies individual
  instances of an entity type.
• atomic or composite
• Criteria
• will not change its value
• never null
• avoid intelligent identifiers
• consider surrogates
• ?

SS
Name
Number
PLAYER
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Attribute Names and Definitions

• Names
• Singular noun
• Unique within table and normally within database
• Standard format (set by organization)
• Consistent use of qualifiers and classes

• Definitions
• What it is, why its important
• What is included (and not)
• Aliases
• Source of values
• Required or optional
• Updateable
• Multiplicity
• Relationships with other attributes

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Relationships

• the glue that holds together the various
  components of an E-R model.
• an association among instances of one or more
  entity types that is of interest
• Relationship type
• Relationship instance
• ?

Has
TEAM
PLAYER
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Relationships

• Attributes may be associated with many-to-many or
  one-to-one relationships
• the attribute is a characteristic of the
  relationship
• not of any of the entities
• Associative entities
• name with gerunds ing not often???
• conditions
• all participating relationships are many
• associative entity has meaning to users
• associative entity has one or more attributes
• associative entity participates in other
  relationships independently of associated
  entities
• the many cardinality terminates at the assoc.
  entity
• ?

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Degree of Relationship

• Unary
• recursive
• person to person
• bill of materials structure
• Binary
• most common
• 11, 1M, MN
• Ternary
• use associative entities
• ?

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Cardinality

• The cardinality of a relationship refers to the
  maximum number of instances in one entity that
  are related to a single instance in the other
  entity.
• one, a specific maximum, or many
• may include minimum as well
• mandatory
• optional
• ?

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Relationship Names and Definitions

• Names
• Verb phrase
• Avoid vague names

• Definitions
• What action is being taken
• Why it is important
• Examples
• Optional participation
• Reason for explicit max.
• Mutually exclusive relationships
• Restrictions on participation
• History to be kept
• Transferability

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