Data Modeling - Database Management - Lecture Slides, Slides of Database Management Systems (DBMS)

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Data Modeling

Objectives

• Explain the concept and practical use of data modeling.
• Recognize which relationships in the business environment are unary, binary, and ternary relationships.
• Describe one-to-one, one-to-many, and many-to- many unary, binary, and ternary relationships.

Essence of Data Modeling

• Exploring the different ways that entities can relate to each other as they always do in the real world
• Devising a way of recording, of diagramming, the entities and the ways in which they interrelate in the business environment

Entity-Relationship (E-R) Model

• A diagramming technique
• Diagrams entities (with attributes) and the relationship between the entities.
• There are many variations of E-R diagrams in use.

E-R Model Entity (and its attributes)

• Entity type’s attributes are shown below the separator line.
• An asterisk denotes attribute(s) that constitute the entity type’s unique identifier.

Relationships

• Associations between entities
• Different kinds:
  • Binary relationships
  • Unary relationships
  • Ternary relationships

Cardinality

• Represents the maximum number of entities that can be involved in a particular relationship. - One-to-One Binary Relationship - One-to-Many Binary Relationship - Many-to-Many Binary Relationship

One-to-One Binary Relationship

• A single occurrence of one entity type can be associated with a single occurrence of the other entity type and vice versa.

Many-to-Many Binary Relationship

• M-M

• “many” can be either an exact number or have a known maximum.

Cardinality

Cardinality & Modality

Intersection Data

• Describes the relationship between two entities.
• Used with many-to-many relationships.
• Represented on E-R diagram in a special five-sided intersection data box, which is attached to the relationship diamond between the two entity boxes.

Associative Entity

• Entities can have attributes; many-to-many relationships can have attributes.
• Many-to-many relationship may be treated similarly to entities in an E-R diagram.

Associative Entity

• Should you diagram as associative entity or many-to-many relationship? - personal taste - follow company standards
• The unique identifier of the associative entity is usually the combination of the unique identifiers of the two entities in the many-to- many relationship.