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2. Relational algebra - Wikipedia

   en.wikipedia.org/wiki/Relational_algebra

   The relational algebra uses set union, set difference, and Cartesian product from set theory, and adds additional constraints to these operators to create new ones.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.

3. Relation algebra - Wikipedia

   en.wikipedia.org/wiki/Relation_algebra

   A relation algebra (L, ∧, ∨, −, 0, 1, •, I, ˘) is an algebraic structure equipped with the Boolean operations of conjunction x∧y, disjunction x∨y, and negation x −, the Boolean constants 0 and 1, the relational operations of composition x•y and converse x˘, and the relational constant I, such that these operations and constants satisfy certain equations constituting an ...

4. Relation (mathematics) - Wikipedia

   en.wikipedia.org/wiki/Relation_(mathematics)

   For example, "1 < 3", "1 is less than 3", and "(1,3) ∈ R less" mean all the same; some authors also write "(1,3) ∈ (<)". Various properties of relations are investigated. A relation R is reflexive if xRx holds for all x, and irreflexive if xRx holds for no x. It is symmetric if xRy always implies yRx, and asymmetric if xRy implies that yRx ...

5. Projection (relational algebra) - Wikipedia

   en.wikipedia.org/.../Projection_(relational_algebra)

   [1] In practical terms, if a relation is thought of as a table, then projection can be thought of as picking a subset of its columns. For example, if the attributes are (name, age), then projection of the relation {(Alice, 5), (Bob, 8)} onto attribute list (age) yields {5,8} – we have discarded the names, and only know what ages are present.

6. Category:Relational algebra - Wikipedia

   en.wikipedia.org/wiki/Category:Relational_algebra

   Download QR code; Print/export ... Pages in category "Relational algebra" ... Selection (relational algebra) String operations This page was ...

7. Composition of relations - Wikipedia

   en.wikipedia.org/wiki/Composition_of_relations

   A small circle () has been used for the infix notation of composition of relations by John M. Howie in his books considering semigroups of relations. [10] However, the small circle is widely used to represent composition of functions g ( f ( x ) ) = ( g ∘ f ) ( x ) {\displaystyle g(f(x))=(g\circ f)(x)} , which reverses the text sequence from ...

8. Selection (relational algebra) - Wikipedia

   en.wikipedia.org/wiki/Selection_(relational_algebra)

   In relational algebra, a selection (sometimes called a restriction in reference to E.F. Codd's 1970 paper [1] and not, contrary to a popular belief, to avoid confusion with SQL's use of SELECT, since Codd's article predates the existence of SQL) is a unary operation that denotes a subset of a relation.

9. Binary relation - Wikipedia

   en.wikipedia.org/wiki/Binary_relation

   Since relations are sets, they can be manipulated using set operations, including union, intersection, and complementation, and satisfying the laws of an algebra of sets. Beyond that, operations like the converse of a relation and the composition of relations are available, satisfying the laws of a calculus of relations , for which there are ...