Chapter 2 Flashcards
(14 cards)
Attribute
Depiction of a characteristic of an entity
- Represents the details that will be recorded for each entity instance
- Within one entity, each attribute must have a different name
Binary Relationship
Relationship between two entities (degree 2 relationship)
Cardinality Constraints
Depict how many instances of one entity can be associated with instances of another entity
Maximum Cardinality
- One (represented by a straight bar: 1)
- Many (represented by a crow’s foot symbol)
Minimum Cardinality (participation)
- Optional (represented by a circular symbol: 0)
- Mandatory (represented by a straight bar: 1)
Composite Attribute
An attribute that has meaningful component parts (attributes).
Database Requirements
It helps keep the focus on asking or seeking answers to the right questions in order to establish the relevant facts about entities, attributes, relationships
Derived Attribute
An attribute whose values can be calculated from related attribute values.
Entity Instances (entity members)
Occurrences of an entity
- Entities themselves are depicted in the er diagrams while entity instances are not
- Entity instances are eventually recorded in the database that is created based on the ER diagram
Entity-Relationship (ER) Modeling - Conceptual Database Modeling Technique
Conceptual database modeling technique
- Enables the structuring and organizing of the requirements collection process
- Provides a way to graphically represent the requirements
ER Diagram (ERD)
The result of ER modeling
- Serves as a blueprint for the database
One to One
straight line to straight line
One to Many
Straight line to crows foot
Relationship
ER modeling construct depicting how entities are related
- Within an ER diagram, each entity must be related to at least one other entity via a relationship
