Relation Algebra Flashcards
What is a query language used for?
Manipulation and retrieval of data from a database
What are the benefits of the relational model?
Support simple, powerful, declarative QL, strong formal foundation based on logic, allows for much optimization
What is the result of a query?
A relation instance
What is a query applied to?
A relation instance
What are the schema of the input and output relations determined by?
The query itself
What’s the difference between relational algebra and relational calculus?
Algebra is more operational, and more specific; but both describe what they want
What is an algebra?
Mathematical system consisting of operands and operators.
What is an operand?
Variable or values from which new values can be constructed
What is an operator?
Symbols denoting procedures that construct new values from given values
What is Relational Algebra?
An algebra whose operands are relations or variables that represent relations and operators that are designed to do the common things on relations. Used as a query language for relations
What are 8 core relational algebra operations?
Union, Intersection, Difference, Selection, Projection, Products, Joins, Renaming
What is a union, intersection, and difference?
Usual set operations that require both operands to have the same relation scheme
What is a selection?
Select Rows
What is a projection?
Project Columns
What are products and joins?
Compositions of relations
