Chapter 3 Database

Entity-relationship model:

A logical representation of the data for an organization or for a business area.

Entity instance:

A single occurrence of an entity type.

Attribute:

A property or characteristic of an entity type that is of interest to the organization. property or characteristic of an entity or relationship type (Column)
Characteristics:
-Required versus Optional Attributes
-Simple versus Composite Attribute
-Single-

Multivalued attribute:

An attribute that may take on more than one value for a given entity instance.

Weak entity:

- An entity type whose existence depends on some other entity type.
-depends on existence of another entity type
-dependent on a strong entity (identifying owner)...cannot exist on its own
-does not have a unique identifier (only a partial identifier)

Derived attribute:

An attribute whose values can be calculated from related attribute values.

Business rule:

-a statement that defines or constrains some aspect of the business.
-Assert business structure
-Control/influence business behavior
Good business rule are:
Declarative
Precise
Atomic
Consistent
Expressible
Distinct
Business-oriented
-scope
-characteristi

Composite Attribute:

can be broken into many component parts

unary relationship

relates instances of a single entity type

degree

number of participating entity types in relationship

ternary

relationship of degree 3

bill of materials

many to many unary relationship

Data Modeling & the SDLC:
Analysis

Database activity-thorough and
integrated conceptual data
modeling

Data Modeling

-Entity relationship model (ER-model)
-Entity relationship diagram (ER-diagram)

Entities:

-Person, place, object, event, concept, etc. (Noun)
-Entity type vs. entity instance (Table vs. Row)
type:
A collection of entities that share common properties or characteristics.
should be:
-An object that will have many instances in the database
-An ob

Relationships:

-Interaction among entity types (Verb)
-Relationship type vs. relationship instance
type:
A meaningful association between (or among) entity types.
Identifying:
-The relationship between a weak entity type and its owner.
-links strong entities to weak ent

Identifier (Key)

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

Candidate Identifier

an attribute that could be a key...satisfies the requirements for being an identifier

Entities can have _____ ______ between them.

multiple relationships

Associative Entity

combination of relationship and
entity
-An entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity instances.
-relationship modeled as an entity type

Degree of relationship

is the number of entity
types that participate in it:
-Unary Relationship
-Binary Relationship
-Ternary Relationship

Cardinality Constraint

specifies the number of instances of one entity that can (or must) be
associated with each instance of another entity:
-One-to-One
-One-to-Many
-Many-to-Many
Specifies the number of instances of one entity that can (or must) be associated with each instan

Minimum Cardinality

-optional
-mandatory

Strong Entities

exist independently of other types of entities

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

-All relationships for the associative entity should be many
-The associative entity could have meaning independent of the other entities
-The associative entity preferably has a unique identifier, and should also
have other attributes
-The associative en