Entity relationship-diagrams
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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.
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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