Data Modelling

Systems Development Life Cycle (SDLC) Model

  graph TD
  ares["Analysis / Requirement Stage"]-->ds["Design Stage"]-->devs["Development Stage"]-->ts["Testing Stage"]-->im["Implementation / Maintenance"]

Requirement Analysis Stage

Sources of requirements:

• User Interviews
• Forms
• Reports
• Queries
• Use Cases
• Business Rules
  • Flow Chart
  • Activity Diagram

Three Stages of Database Development

• Requirement Analysis Stage
• Component Design Stage
• Implementation Stage

They are part of SDLC model.

Entity Relationship (E-R) Model

Important Elements

• Entities
• Attributes
• Identifiers
• Relationships

Entity

Entity Class is a description of the structure and format of the occurrences of the entity.

Entity Instance is a specific occurrence of an entity within an entity class.

Attributes

Attributes describe characteristics of entities.

Attributes have a data type and properties.

Identifiers

Entity instances have identifiers.

An identifier will identify a particular instance in the entity class.

Identifier Types

• Uniqueness
  • Identifiers may be unique or non-unique.
  • If the identifier is unique, then the data value for the identifier must be unique for all instances.
• Composite
  • A composite identifier consists of two or more attributes.

Relationships

Entities can be associated with one another in relationships.

Relationship degree defines the number of entity classes participating in the relationship:

• Degree 1 is a unary relationship.
• Degree 2 is a binary relationship.
• Degree 3 is a ternary relationship.

Maximum Cardinality

It is the maximum number of entity instances that may participate in a relation instance.

1:1 (One-to-One)

A single entity instance in one entity class is related to a single entity instance in another entity class.

  graph LR
  em["EMPLOEE"]---rate{"1:1"}---lc["LOCKER"]

1:N (One-to-Many)

A single entity instance in one entity class is related to many entity instances in another entity class.

  graph LR
  item["ITEM"]---rate{"1:N"}---qu["QUOTATION"]

N:M (Many-to-Many)

Many entity instances in one entity class are related to many entity instances in another entity class

  graph LR
  item["ITEM"]---rate{"N:M"}---su["SUPPLIER"]

Minimum Cardinality

It is the minimum number of entity instances that must participate in a relationship instance.

These values typically assume a value of zero (optional) or one (mandatory).