ERD Flashcards
What is an Entity Relationship Diagram (ERD)?
An expressive and powerful tool that helps to capture the organization of data within a system into entities, and the realtions among them.
What is a graphical representation of Entities and their relationships?
Entity Relationship Diagram
What can anything that is a source of related data considered?
An entity
What type of process is drawing an ERD?
Iterative (a process for calculating a desired result by means of a repeated cycle of operations.)
How is an entity in an ERD represented?
An Entity name in uppercase inside a box
What do the name and box of an entity represent?
A complete class of simlitar entities.
For example, an entity called “employee” doesn’t represent a particular employee in the business, but represents all employees in the business.
What do entities ultimately become?
A file, inside each file will be a record for each employee the business has.
For an entity named Employee.
What is each “record” kept with in an entity called?
An entity instance.
What is an entity a collection of?
Entity Instances
What are the fields housed in entity instances called?
Entity attributes
What type of entity is defined more or less completely by the data that it holds?
A Strong Entity
Example: Employee, Student, Vehicle, Patient, Manager etc.
What is an entity that depends on other entities to be completely defined?
A weak entity
Examples: An entity like dependents that is reliant on an employee entity first.
What is an entity that describes relations?
An associative entity
What are fields of data that we gather from an entity?
An attribute
What does an attribute contain?
The actual pieces of data that are being stored in the database.
Examples are names, addressess, ages, quantities etc.
What is an attribute that unequivocally identifies an individual entity?
An Identifier attribute.
Examples: SSN for individuals, Student IDs for students etc.
How are identifier attributes indicated in an ERD?
By underlining their name
What are attributes that identify individual entity instances within a weak entity?
Partial Idenifier attributes
Examples: SSN of an employee’s dependent.
How are partial identifiers indicated in an ERD?
By double underlining their name
Which attribute is an attribute whose contents can be calculated or obtained by applying an algorithm to other fields in the database?
A Derived attribute.
How is a derived attribute indicated in an ERD?
By surrounding the name with [].