ER Model Flashcards
What are the 6 database design steps?
- Requirements
- Conceptual Design (ER Model)
- Logical Design (Relational DM, Output: schema)
- Scheme Refinment
- Physical Database Design
- Application and Security Design
What is the purpose of the ER model?
Sketch database designs to see the kinds of data and how they connect
What is an entity?
A thing or object; Eg: Student
What is an entity set?
A collection of similar entities; ex Students in UF
What is an attribute?
A property of an entity
What is a relationship?
Connects two or more entity sets
What are roles?
Roles are used when an entity set appears more than once in a relationship. Use edges between the relationship and entity set with names called roles.
What are many-many relationships?
An entity set can be connected to many to many entities of the other set. No participation constraints.
What are the many-one relationships and how are they represented?
Use an arrow entering the one side. Rounded arrow is exactly one; regular arrow is at most one.
How are one-to-one relationships represented?
An arrow entering both entity sets.
When are weak entity sets used?
When entities need help to identify them uniquely
How are weak entities represented?
Double diamond for supporting many-to-one with total participation (exactly one).
Double rectangle for weak entity set.
What is the key for a weak entity set?
Its own underlined attributes and the keys for the supporting entity sets.
What is aggregation?
Allows us to treat a relationship set as an entity set for purposes of participation in other relationships.
What are 3 design techniques for ER?
- Avoid redundancy
- Don’t use an entity set when an attribute will do
- Limit weak entity sets
