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  2. Cardinality - Wikipedia

    en.wikipedia.org/wiki/Cardinality

    The picture shows an example f and the corresponding T; red: n∈f(n)\T, blue:n∈T\f(n). While the cardinality of a finite set is simply comparable to its number of elements, extending the notion to infinite sets usually starts with defining the notion of comparison of arbitrary sets (some of which are possibly infinite).

  3. Cardinality (data modeling) - Wikipedia

    en.wikipedia.org/wiki/Cardinality_(data_modeling)

    Within data modelling, cardinality is the numerical relationship between rows of one table and rows in another. Common cardinalities include one-to-one , one-to-many , and many-to-many . Cardinality can be used to define data models as well as analyze entities within datasets.

  4. Cardinal number - Wikipedia

    en.wikipedia.org/wiki/Cardinal_number

    The notion of cardinality, as now understood, was formulated by Georg Cantor, the originator of set theory, in 1874–1884. Cardinality can be used to compare an aspect of finite sets. For example, the sets {1,2,3} and {4,5,6} are not equal, but have the same cardinality, namely three.

  5. Bijection, injection and surjection - Wikipedia

    en.wikipedia.org/wiki/Bijection,_injection_and...

    4 Examples. 5 Properties. 6 Category theory. 7 History. 8 See also. 9 References. ... the two sets are said to have the same cardinality. Likewise, one can say that ...

  6. Aleph number - Wikipedia

    en.wikipedia.org/wiki/Aleph_number

    The set of all finite ordinals, called ω or ω 0 (where ω is the lowercase Greek letter omega), has cardinality ℵ 0. A set has cardinality ℵ 0 if and only if it is countably infinite, that is, there is a bijection (one-to-one correspondence) between it and the natural numbers. Examples of such sets are

  7. Cardinality of the continuum - Wikipedia

    en.wikipedia.org/wiki/Cardinality_of_the_continuum

    In set theory, the cardinality of the continuum is the cardinality or "size" of the set of real numbers, sometimes called the ... as in the first two examples.)

  8. Many-to-many (data model) - Wikipedia

    en.wikipedia.org/wiki/Many-to-many_(data_model)

    For example, think of A as Authors, and B as Books. An Author can write several Books, and a Book can be written by several Authors. In a relational database management system, such relationships are usually implemented by means of an associative table (also known as join table, junction table or cross-reference table), say, AB with two one-to-many relationships A → AB and B → AB.

  9. Cardinal function - Wikipedia

    en.wikipedia.org/wiki/Cardinal_function

    The most frequently used cardinal function is the function that assigns to a set A its cardinality, denoted by |A|. Aleph numbers and beth numbers can both be seen as cardinal functions defined on ordinal numbers. Cardinal arithmetic operations are examples of functions from cardinal numbers (or pairs of them) to cardinal numbers.