32 terms

Database Design-Chapter 5

Data Model
Plan or blueprint for a database design. It's more generalized and abstract than design. It's easier to change than a design.
E-R Model
Set of concepts and graphical symbols that can be used to create conceptual schemas
Original ER
Peter Chen-1976
Information Engineering
James Martin, 1990, it uses crow's foot notation, it's easier to understand
National standard developed by the National Institute of Standards and Technology.
UML-Unified Modeling Language
The Object Management Group; it supports object-oriented methodology.
Entity Class
A collection of entities of a given type
Entity Instance
The occurrence of a particular entity
Originally shown as ellipses. Now they are shown in rectangular form.
Attributes that name, or identify entity instances. The Consists of one or more of the entity's attributes
Relationship classes
Associations among entity classes
Relationship instances
Associations among entity instances
The number of entity classes in the relationship
Means count
One-to-One relationship
The entity on the one side of the relationship is called the parent entity . The entity on the child side of the relationship is called the child entity.
Minimum Cardinality
Zero if participation in the relationship is optional, 1 if the relationships is required or mandatory. (hash mark)
ER properities
Cannot indicate true minimum cardinalities on N:M relationships. Must use intersection table instead of true N:M model.
ID-Dependent Entities
An entity whose identifier includes the identifier of another entity.
ID-Dependent Entities Properties
Minimum cardinality to the parent is always one (required.) A solid line is used to identify ID-dependent entities.
Weak entity
An entity whose existence depends upon another entity
Weak entity properties
All ID-Dependent entities are weak, but not all weak entities are ID-dependent. Indicated by non-identifying relationship
Subtype Entity
A special case of a super-type entity that contains specific attributes
Supertype entity
Contains all common attributes.
One supetype relates to at most one subtype. Ex. Employee can be a manager or DB Admin, but not both.
One supertype can relate to one or more subtypes. Ex. Employee can be admin or Manager
HAS-A Relationship
Strong entity relationships because each entity instance HAS A relationship with another entity instance.
IS-A Relationship
Supertypes/Subtypes relationships are called IS-A relationships because a subtype IS A supertype.
Data model process 1
Analyze the business documents
Data model process 2
Identify all potential entities, including identifier and attributes for each entity
Data model process 3
Specify relationships (Both max & Min cardinality
Data model process 4
Create the E-R Model
Data model process 5
Validate the model by showing the designed forms and reports to customers.