Reference

Reference is a relation 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. The second object – the one to which the first object refers – is called the referent of the first object.

The term reference is used in many spheres of human knowledge, adopting shades of meaning particular to the contexts in which it is used.

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; but, other concrete and abstract contexts exist as methods of defining references within the scope of the various fields that require an origin, point of departure, or an original form. This includes methods that intentionally hide the reference from some observers, as in cryptography.

The following sections give specific usages of reference in different subjects.

Etymology
The word reference is derived from Middle English referren, from Middle French référer, from Latin referre, "to carry back", formed from the prefix re- and ferre, "to bear". A large number of words derive from this root, including referee, referent, referendum, all retaining the basic meaning of the original Latin as "a point, place or source of origin" in terms of which something of comparable nature can be defined. A referee is the provider of this source of origin, and a referent is the possessor of the source of origin, whether it is knowledge, matter or energy.

Computer science
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.

The C++ programming language has a specific type of reference also referred to as a "reference"; see reference (C++).

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

Bibliographies
Bibliographies are special reference works that are used to identify as many published works on a given subject as possible, and serve as compilations for other authors or researchers.

Library and information sciences
In a library, "reference" may refer to a dictionary, an encyclopedia or other reference work, that contains many brief articles that cover a broad scope of knowledge in one book, or a set of books. However, the word reference is also used to mean a book that cannot be taken from the room, or from the building. Many of the books in the reference department of a library are reference works, but some are books that are simply too large or valuable to loan out. Conversely, selected reference works may be shelved with other circulating books, and may be loaned out.

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).

Librarians also conduct reference interviews at the library reference desks, to help people find the information they seek. Help may also be available outside the library though virtual reference and digital reference services.

Encyclopedias & books of facts
Some published sources are produced as reference works that allow quick access to essential information about given subjects, sometimes compiled as topical collections, and sometimes as general collections of entries.

Psychology
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 laso lead to circular reasoning, preventing evolution of thought.

Economics and business
In the labour market, potential employers often ask job applicants for references or recommendations, so that their suitability can be verified independently. The references can be a written letter, but are often just a contact telephone number. Employers can ask for professional references, which are from former employers, or for character references, which are from people of distinction such as doctors or teachers. The source of the reference must be well known to the applicant and able to vouch for their abilities during employment.

In business administration, terms of reference describe the purpose and structure of a project, committee, meeting, negotiation, or any similar collection of people who have agreed to work together to accomplish a shared goal. The terms of reference of a project are often referred to as the project charter.

In business marketing and public procurement and tenders references are often used within the field of engineering, consultancy, industry and construction contracts. References are used to examine a company's ability to deliver the required level of service. Very often bigger companies will have hundreds or even thousands of references and will often try to categorize and manage them with reference management software.

Education
In academics and scholarship, an author-title-date information in bibliographies and footnotes, specifying complete works of other people. Copying of material by another author without proper citation or without required permissions is plagiarism.

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 reference has been developing since the 19th Century.

In scholarship, a reference may be a citation of a text that has been used in the creation of a piece of work such as an essay, report, or oration. Its primary purpose is to allow people who read such work to examine the author's sources, either for validity or to learn more about the subject. Such items are often listed at the end of an article or book in a section marked "Bibliography" or "References". A bibliographical section often contains works not cited by the author, but used as background reading or listed as potentially useful to the reader. A reference section contains all of the works and only those works cited by the author(s) in the main text.

Law
In law, references are documents or people providing witness to character. This connotation is also used in employment.

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.

In Canadian law, a reference question is a procedure through which the government can submit legal questions to the Supreme Court of Canada and provincial governments to the provincial courts of appeal.

Semantics
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 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
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.

Absent referent
Words can often be meaningful without having a concrete here-and-now referent. Fictional and mythological names such as "Bo-Peep" and "Hercules" illustrate this possibility. Sign links with absent referents also allow for discussing abstract ideas ("love," "peace") as well as people and events of the past and future.

For those who argue that one cannot directly experience the divine (e.g. God), the sign "God" can serve as an example of a reference with an absent referent. Additionally, certain sects of Judaism and other religions consider it sinful to write, discard, or deface the name of the divine. To avoid this problem, the signifier G-d is sometimes used, though this could be seen as a sign that refers to another sign with an absent referent.

Linguistic sign
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.

Mathematics
In mathematics, the absent referent can be seen with the symbol for zero, "0" or the empty set, "{ }".

A reference point in Geometry is a location used to describe another point, by giving the relative position. Similarly there is the concept of frame of reference (both in physics and figuratively) and benchmark (in surveying and figuratively).

Engineering
In engineering a reference design is often used during the pre-production phase of design development to test design features against original specifications.

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

Literature and rhetoric
In academic literature, a reference is a previously published written work within academic publishing that has been used as a source for theory or claims referred to that are used in the text. References contain complete bibliographic information so the interested reader can find them in a library. References can be added either at the end of the publication or as footnotes.

In publishing, a reference is citation of a work, in a footnote, from which an idea was taken.