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=                             Reference                              =
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                            Introduction
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Reference is a relationship between objects in which one object
designates, or acts as a means by which to connect to or link to,
another object. The first object in this relation is said to 'refer
to' the second object. It is called a 'name' for the second object.
The second object, the one to which the first object refers, is called
the 'referent' of the first object. A name is usually a phrase or
expression, or some other symbolic representation. Its referent may be
anything - a material object, a person, an event, an activity, or an
abstract concept.

References can take on many forms, including: a thought, a sensory
perception that is audible (onomatopoeia), visual (text), olfactory,
or tactile, emotional state, relationship with other, spacetime
coordinate, symbolic or alpha-numeric, a physical object or an energy
projection. In some cases, methods are used that intentionally hide
the reference from some observers, as in cryptography.

References feature in many spheres of human activity and knowledge,
and the term adopts shades of meaning particular to the contexts in
which it is used. Some of them are described in the sections below.


                       Etymology and meanings
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The word 'reference' is derived from Middle English ', from Middle
French 'référer', from Latin 'referre', "to carry back", formed from
the prefix 're'- and 'ferre', "to bear". A number of words derive from
the same root, including 'refer', 'referee', 'referential',
'referent', 'referendum'.

The verb 'refer (to)' and its derivatives may carry the sense of "link
to" or "connect to", as in the meanings of 'reference' described in
this article. Another sense is "consult"; this is reflected in such
expressions as reference work, reference desk, job reference, etc.


                             Semantics
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In semantics, reference is generally construed as the relationships
between nouns or pronouns and objects that are named by them. Hence,
the word "John" refers to the person John. The word "it" refers to
some previously specified object. The object referred to is called the
'referent' of the word. Sometimes the word-object relation is called
"denotation"; the word denotes the object. The converse relation, the
relation from object to word, is called "exemplification"; the object
exemplifies what the word denotes. In syntactic analysis, if a word
refers to a previous word, the previous word is called the
"antecedent".


Meaning
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Gottlob Frege argued that reference cannot be treated as identical
with meaning: "Hesperus" (an ancient Greek name for the evening star)
and "Phosphorus" (an ancient Greek name for the morning star) both
refer to Venus, but the astronomical fact that '"Hesperus" is
"Phosphorus"' can still be informative, even if the "meanings" of
"Hesperus" and "Phosphorus" are already known. This problem led Frege
to distinguish between the sense and reference of a word. Some cases
seem to be too complicated to be classified within this framework; the
acceptance of the notion of secondary reference may be necessary to
fill the gap. See also Opaque context.


Linguistic sign
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The very concept of the linguistic sign is the combination of content
and expression, the former of which may refer entities in the world or
refer more abstract concepts, e.g. thought.
Certain parts of speech exist only to express reference, namely
anaphora such as pronouns. The subset of reflexives expresses
co-reference of two participants in a sentence.  These could be the
agent (actor) and patient (acted on), as in "The man washed himself",
the theme and recipient, as in "I showed Mary to herself", or various
other possible combinations.


                          Computer science
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In computer science, references are data types that refer to an object
elsewhere in memory and are used to construct a wide variety of data
structures, such as linked lists. Generally, a reference is a value
that enables a program to directly access the particular data item.
Most programming languages support some form of reference. For the
specific type of reference used in the C++ language, see reference
(C++).

The notion of reference is also important in relational database
theory; see referential integrity.


                  Library and information sciences
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References to many types of printed matter may come in an electronic
or machine-readable form. For books, there exists the ISBN and for
journal articles, the Digital object identifier (DOI) is gaining
relevance. Information on the Internet may be referred to by a Uniform
Resource Identifier (URI).


                             Psychology
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In terms of mental processing, a self-reference is used in psychology
to establish identification with a mental state during self-analysis.
This seeks to allow the individual to develop own frames of reference
in a greater state of immediate awareness. However, it can also lead
to circular reasoning, preventing evolution of thought.

According to Perceptual Control Theory (PCT), a reference condition is
the state toward which a control system's output tends to alter a
controlled quantity. The main proposition is that "All behavior is
oriented all of the time around the control of certain quantities with
respect to specific reference conditions."


          {{anchor|Bibliographical reference}}Scholarship
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In academics and scholarship, a reference or bibliographical reference
is a piece of information provided in a footnote or bibliography of a
written work such as a book, article, essay, report, oration or any
other text type, specifying the written work of another person used in
the creation of that text. A bibliographical reference mostly includes
the full name of the author, the title of their work and the year of
publication. The primary purpose of references is to allow readers to
examine the sources of a text, either for validity or to learn more
about the subject. Such items are often listed at the end of a work in
a section marked 'References' or 'Bibliography'.

References are particularly important as for the use of citations,
since copying of material by another author without proper reference
and / or without required permissions is considered plagiarism, and
may be tantamount to copyright infringement, which can be subject to
legal proceedings. A 'reference' section contains only those works
indeed cited in the main text of a work. In contrast, a
'bibliographical' section often contains works not cited by the
author, but used as background reading or listed as potentially useful
to the reader.

Keeping a diary allows an individual to use references for personal
organization, whether or not anyone else understands the systems of
reference used. However, scholars have studied methods of reference
because of their key role in communication and co-operation between
'different' people, and also because of misunderstandings that can
arise. Modern academic study of bibliographical references has been
developing since the 19th century.


                                Law
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In patent law, a reference is a document that can be used to show the
state of knowledge at a given time and that therefore may make a
claimed invention obvious or anticipated. Examples of references are
patents of any country, magazine articles, Ph.D. theses that are
indexed and thus accessible to those interested in finding information
about the subject matter, and to some extent Internet material that is
similarly accessible.


                                Arts
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In art, a reference is an item from which a work is based. This may
include:
* an existing artwork
* a reproduction (i.e., a photo)
* a directly observed object (e.g., a person)
* the artist's memory
Another example of reference is samples of various musical works being
incorporated into a new one.


                              See also
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*Antecedent (grammar)
*Exemplification
*Generic antecedent
*Hyperlink
*Indexicality
*ISO 690
*Recommendation letter
*Signified and signifier


                           External links
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*[http://www.reference.com/ Reference.com] - a multi-source
encyclopedia search service, and language reference products provider
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*[http://www.references.net/ References.net] - a directory of
multidisciplinary reference resources on the web
*[http://www.refmuseum.com/ Refmuseum.com] - The online museum of
references


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