WGU C192 Lesson 5 Flashcards

Study Notes

Selection (σpredicate (R)): Filters tuples in relation R based on a specified condition (predicate).
Projection (Πa1..., an(R)): Extracts specified attributes from relation R, removing duplicates to form a vertical subset.
Union (R u S): Combines tuples from relations R and S, eliminating duplicates. R and S must be union-compatible.
Set Difference (R - S): Produces a relation of tuples in R that are not present in S, requiring union-compatibility.
Intersection (R ∩ S): Yields a relation including tuples found in both R and S, contingent on union-compatibility.
Cartesian Product (R x S): Generates a relation by concatenating every tuple from R with every tuple from S.
Rename (ρS(E) or ρS(a1, a2,..., an)(E)): Creates a new name S for expression E, and optionally renames the attributes.

Theta Join (R ⋈FS): Forms a relation from tuples satisfying predicate F in the Cartesian product of R and S, where F uses comparison operators.
Natural Join (R ⋈ S): An equijoin over common attributes of R and S, eliminating duplicate occurrences of common attributes.
Left Outer Join (R ⋊ S): Includes tuples from R without matching values in S, assigning nulls to missing values in S.
Semijoin (R ▹F S): Returns tuples from R participating in the join with S that satisfy predicate F.

Division (R ÷ S): Creates a relation of tuples from R that match all combinations of tuples in S.
Aggregate Function Application (ℑAL(R)): Applies aggregation defined by AL to relation R.
Grouped Aggregate Function (GAℑAL(R)): Groups tuples by attributes GA and then applies AL to generate a new relation.

Predicate Calculus: A branch of symbolic logic focusing on truth-valued functions with arguments.
Tuple Calculus: A type of predicate calculus pertaining specifically to tuples in databases.
Domain Relational Calculus: A form of predicate calculus that uses domain variables sourced from attribute domains.
Propositions: Truth-valued expressions resulting from substituting values into a predicate.

Relational Algebra: A high-level procedural language that directs a DBMS to construct new relations from existing ones.
Relational Calculus: A non-procedural language that formulates definitions for relations based on existing database relations.
Rationally Complete: Describes a language capable of generating any relation derivable through relational calculus.

Five Core Operations: Include selection, projection, Cartesian product, union, and set difference, crucial for relational algebra.

Classification: Relational data manipulation languages can be procedural/non-procedural and include various generational classifications such as fourth- and fifth-generation languages.