Chapter 3: Entity Relationship Modelling

Chapter 3: Entity Relationship Modelling

1. Data need to be organized so that they can be processed effectively in producing useful information

2. Three (3) basic concepts of E-R model are: Entity type, Attributes, Relationship type

3. Entity Type

   • Strong Entity : An entity whose existence is independent
   • Weak Entity: An entity whose existence is dependent on some other entity.

4. Attribute: Represents the properties of an entity or a relationship type

   • Candidate Key
   • Primary Key
   • Composite Key
   • Alternate Key
   • Foreign Key
   • Super Key
   • Simple attribute, Composite attribute, Single-valued attribute, Multi-valued attribute, Derived attribute

5. Relationship type: A meaningful association among entity types.

   • Strong Relationship
   • Weak Relationship
   • Recursive Relationship

6. STRUCTURAL CONSTRAINTS

   • Cardinality constraint
     • 1:1 (one-to-one), 1:M (one-to-many)c, M:N (many-to-many)
   • Participation constraint
     • Total (mandatory), Partial (optional)

7. PROBLEM WITH E-R MODEL

   • Fan traps, Chasm traps

8. Superclasses and Subclasses of Entity Types

   • Superclass: An entity type that includes distinct subclasses required to be represented in a data model
   • Subclass: An entity type that has a distinct role and is also a member of a superclass

9. Specialization: The process of maximizing the differences between members of an entity by identifying their distinguishing characteristics

10. Generalization: The process of maximizing the differences between entities by identifying their common features

11. Aggregation: The process that enable a set of relations seen as one project