What is self-referential integrity constraint ?
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Answer Posted / datta
Self-reference occurs in natural or formal languages when a
sentence or formula refers to itself. The reference may be
expressed either directly; through some intermediate
sentence or formula; or by means of some encoding. In
philosophy, it also refers to the ability of a subject to
speak of or refer to himself, herself, or itself: to have
the kind of thought expressed by the first person pronoun,
the word "I" in English. Self-reference is related to self-
reflexivity and apperception.
Self-reference is studied and has applications in
mathematics, philosophy, computer programming, and
linguistics. Self-referential statements sometimes have
paradoxical behavior.
Contents [hide]
1 Usage
2 Examples
2.1 Words
2.2 Mathematics
2.3 Sentences
2.4 Linguistics
2.5 The Fumblerules
2.6 Literature
3 See also
4 References
5 External links
Usage
The Ouroboros, a dragon that continually consumes itself,
is used as a symbol for self-reference.[citation needed]An
example of a self-referential situation is the one of
autopoiesis, as the logical organization produces itself
the physical structure which creates itself.
In metaphysics, self-reference is subjectivity,
while "hetero-reference", as it is called (see Niklas
Luhmann), is objectivity.[citation needed]
Self-reference also occurs in literature and film when an
author refers to his work in the context of the work
itself. Famous examples include Cervantes's Don Quixote,
Denis Diderot's Jacques le fataliste et son maître, Italo
Calvino's If on a winter's night a traveler, many stories
by Nikolai Gogol, Lost in the Funhouse by John Barth, Luigi
Pirandello's Six Characters in Search of an Author, and
Federico Fellini's 8½ . This is closely related to the
concepts of breaking the fourth wall and meta-reference,
which often involve self-reference.
The surrealistic painter René Magritte is famous for his
self-referential works. His painting The Treachery of
Images, shown above, includes words claiming, in French,
that it is not a pipe, the truth of which depends entirely
on whether the word "ceci" (in English, "this") refers to
the pipe depicted—or to the painting or the sentence itself.
In computer science, self-reference occurs in reflection,
where a program can read or modify its own instructions as
if they were data. Numerous programming languages support
reflection to some extent with varying degrees of
expressiveness. Additionally, self-reference is seen in
recursion (related to the mathematical recurrence
relation), where a code structure refers back to itself
during computation.
Examples
Many of the following examples appear in Douglas
Hofstadter's Gödel, Escher, Bach: an Eternal Golden Braid,
Metamagical Themas, or I Am a Strange Loop.
Words
A word that describes itself is called an autological word
(or autonym). This generally applies to adjectives, for
example sesquipedalian, but can also apply to other parts
of speech, such as TLA, as a three-letter abbreviation for
three-letter abbreviation, and PHP which is a recursive
acronym for "PHP: Hypertext Preprocessor".
See: Appendix:Autological words.
Mathematics
Impredicativity
Loop (graph theory)
Tupper's self-referential formula
Sentences
"Yields falsehood when preceded by its quotation" yields
falsehood when preceded by its quotation. (This is a
version of the liar paradox, an example of indirect self-
reference through a quine, which leads to a paradox.)
Russell's paradox: The set of all sets which are not
elements of themselves (which includes, and therefore does
not, and therefore does include itself)
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