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  2. Relation (database) - Wikipedia

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

    An attribute value is an attribute name paired with an element of that attribute's domain, and a tuple is a set of attribute values in which no two distinct elements have the same name. Thus, in some accounts, a tuple is described as a function , mapping names to values.

  3. Tuple relational calculus - Wikipedia

    en.wikipedia.org/wiki/Tuple_relational_calculus

    (t.name = "Codd") — tuple t has a name attribute and its value is "Codd" Book(t) — tuple t is present in relation Book. The formal semantics of such atoms is defined given a database db over S and a tuple variable binding val : V → T D that maps tuple variables to tuples over the domain in S: v.a = w.b is true if and only if val(v)(a ...

  4. Relational model - Wikipedia

    en.wikipedia.org/wiki/Relational_model

    The body is a set of tuples. A tuple is a collection of n values, where n is the relation's degree, and each value in the tuple corresponds to a unique attribute. [6] The number of tuples in this set is the relation's cardinality. [7]: 17–22 Relations are represented by relational variables or relvars, which can be reassigned.

  5. Relational calculus - Wikipedia

    en.wikipedia.org/wiki/Relational_calculus

    The relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that is part of the relational model for databases and provide a declarative way to specify database queries.

  6. Row (database) - Wikipedia

    en.wikipedia.org/wiki/Row_(database)

    The implicit structure of a row, and the meaning of the data values in a row, requires that the row be understood as providing a succession of data values, one in each column of the table. The row is then interpreted as a relvar composed of a set of tuples , with each tuple consisting of the two items: the name of the relevant column and the ...

  7. Database model - Wikipedia

    en.wikipedia.org/wiki/Database_model

    Thus, the "relation" in "relational database" refers to the various tables in the database; a relation is a set of tuples. The columns enumerate the various attributes of the entity (the employee's name, address or phone number, for example), and a row is an actual instance of the entity (a specific employee) that is represented by the relation.

  8. Column family - Wikipedia

    en.wikipedia.org/wiki/Column_family

    In analogy with relational databases, a column family is as a "table", each key-value pair being a "row". Each column is a tuple consisting of a column name, a value, and a timestamp. In a relational database table, this data would be grouped together within a table with other non-related data. Two types of column families exist:

  9. Superkey - Wikipedia

    en.wikipedia.org/wiki/Superkey

    Tuples in a relation are by definition unique, with duplicates removed after each operation, so the set of all attributes is always uniquely valued for every tuple. A candidate key (or minimal superkey) is a superkey that can't be reduced to a simpler superkey by removing an attribute.