The document provides an introduction to entity-relationship (E-R) diagrams and modeling, emphasizing three primary constructs: entities, relationships, and attributes. It describes various attribute types, such as composite, multi-value, and derived attributes, and outlines how relationships between entities are categorized, including one-to-one, one-to-many, and many-to-many relationships. Additionally, it includes guidelines for naming and defining relationships to ensure clarity and precision in data modeling.

1. Entity Relationship Diagrams

2. Introduction to Entity-Relationship
Modeling
• Notation makes use of three primary constructs
– Data entities
– Relationships
– Attributes
• Entity-Relationship (E-R) Diagram
– The detailed, logical representation of the entities,
associations and also data elements with an organization
or business.

3. 3 Level Database Design

4. Key Terms
• Entity
– The person, place, object, event or even
concept within the user environment
regarding that the organization wishes in
order to maintain data.
– Symbolized with a rectangle within E-R diagrams.
• Entity Type
– A collection of entities that share typical properties or
even characteristics.

5. Depicting Entities and Attributes

6. Attribute
• Attribute : A named property or even characteristic of an
entity that's associated with interest for an organization.

7. Other Attribute Types
• Composite attribute
– An attribute that may be further divided into much
more attributes
• For example: Name, Address, and so on.
• Multi-Value Attribute
– An attribute which permit several values
• For example: skills, phone numbers, and so on.

8. Cont..
• Derived attribute
– Attributes that may be calculated (derived) through
additional attributes
• For example: age, total, interest, due date, etc
• Unlike the relational model, these types of attribute tend
to be permitted within conceptual models.

9. Relationship
• Relationship explains how entities tend to be
associated.
• Relationship features
– Cardinality
• Entity instance’s participation count
– Degree of relationship
• How many entities are involved in a relationship?

10. One-to-One Relationship
• One-to-One (1:1)
A governor governs (only) one state; a state
has (only) one governor.

11. One-to-Many Relationship
• One-to-Many (1:N) : A single entity instance in a single
entity class (parent) relates to several entity instances
within an additional entity class (child).

12. Many-to-Many Relationship
• Many-to-Many (N:M) : Every entity instance in a single
entity class relates to several entity instances within an
additional entity class and vice versa.

13. Naming and Defining Relationships
• Relationship name is a verb phrase.
• Avoid vague names
• Guidelines with regard to determining associations
– Definition explains what action is being taken as well
as the reason why it is necessary
– Provide good examples in order to clarify the action
– Optional participation should be described
– Clarify causes of any kind of explicit maximum
cardinality

14. Naming and Defining Relationships
• Guidelines with regard to determining relationships
– Clarify any kind of restrictions on participation within
the relationship
– Clarify extent of the history that is kept within the
relationship
– Clarify whether an entity instance involved with the
relationship instance can transfer participation to
another relationship instance

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