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2. Projection (relational algebra) - Wikipedia

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

   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.

3. Selection (relational algebra) - Wikipedia

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

   Mutation and Selection. 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.

4. 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.

5. Relation algebra - Wikipedia

   en.wikipedia.org/wiki/Relation_algebra

   In mathematics and abstract algebra, a relation algebra is a residuated Boolean algebra expanded with an involution called converse, a unary operation.The motivating example of a relation algebra is the algebra 2 X 2 of all binary relations on a set X, that is, subsets of the cartesian square X 2, with R•S interpreted as the usual composition of binary relations R and S, and with the ...

6. Projection (mathematics) - Wikipedia

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

   For example, the mapping that takes a point (x, y, z) in three dimensions to the point (x, y, 0) is a projection. This type of projection naturally generalizes to any number of dimensions n for the domain and k ≤ n for the codomain of the mapping. See Orthogonal projection, Projection (linear algebra). In the case of orthogonal projections ...

7. Florida woman gives insane excuse for why she snatched 3-year ...

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   A Florida woman who allegedly snatched a three-year-old boy from his fenced-in yard and ran off down the street last week told the cops she shouldn’t be arrested because she “gave it back ...

8. 15 Fast Food Restaurants That Don't Use Real Cheese - AOL

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   It does use real cheese for its cheese curds, but other products, for example, its Cheeseburger and Backyard Bacon Ranch Signature Stackburger, use processed cheese. Francis Dean / Getty.

9. Vagus nerve stimulation may relieve treatment-resistant ...

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   Vagus nerve stimulation therapy improved the symptoms of treatment-resistant depression for nearly 500 participants in a major clinical trial.