Modeling Data in the Organization

business rule

statement that defines or controls how data is created, stored,

related, or used in an organization.

business rule

In database design, business rules describe the policies, procedures, and constraints

that guide how entities, attributes, and relationships should be modeled.

Reducing Ambiguity

Well-defined business rules establish a shared vocabulary, preventing inconsistent

data by clarifying key terms for stakeholders.

Guiding Data Constraints

Business rules guide cardinality, participation, and key constraints in ER models,

defining relationships and uniqueness.

Iterative Validation

Iterative validation means reviewing the data model again and again to make sure

it is correct, complete, and aligned with how the organization really works.

Entity Types

An entity type is a group or class of objects, persons, places, events, or concepts about which an

organization wants to store data.

Strong Entity Type

an entity that

can exist independently and has its

own primary key.

Weak Entity Type

an entity that

cannot exist without another

entity. It depends on a strong entity

for identification or existence.

Associative Entity Type

is used

to represent a many-to-many

relationship between two entities.

It often contains attributes that

describe the relationship.

Attributes

An attribute is a property or characteristic that describes an entity.

Simple

Cannot be subdivided

Composite

Can be broken into

components

Multivalued

Multiple values per entity

Derived

Calculated from other

attributes

Key

Uniquely identifies an entity

Entity-Relationship Model

conceptual tool used

to describe data and its relationships in an organization.

Entity Relationships

Relationships link entity types, representing interactions like

'places', 'enrolls in', or 'manages' in organizational data.

Cardinality Types

Cardinality defines how many instances of one entity relate to

another, such as one-to-one, one-to-many, or many-to-many.

Participation Constraints

Participation constraints indicate if entity participation in

relationships is mandatory or optional, guiding data validity.

Relationship Attributes

Some relationships have attributes like Grade or

DateEnrolled that describe the association rather than

individual entities.

Relationship

an association between two or

more entity types.

One-to-One Relationship

One record in Entity A is related to one record in Entity B.

Example: PERSON owns PASSPORT

One-to-Many Relationship

One record in Entity A is related to many records in Entity B.

Example: CUSTOMER places ORDER

One customer can place many orders.

Many-to-Many Relationship

Many records in Entity A are related to many records in

Entity B.

Example: STUDENT enrolls COURSE

Many students can enroll in many courses.

Supertype

an entity type that relates to one or more

subtypes. (Ex. Person)

Subtype

subgroup of entities with unique attributes.

(Ex. Employee, Student)

Inheritance

the concept that subtype entities inherit the

values of all supertype attributes. Its purpose is to reduce

redundancy of similar attributes.

DISJOINT (d)

an entity instance can belong to only one of the

connected subtypes or relationships, not more than one.

OVERLAPPING (o)

an entity instance may belong to more

than one subtype at the same time.

Specialization

divides a supertype into

subtypes

Generalization

combines entities into a

common supertype.