Annotation is extra information associated with a particular point in a document or other piece of information.

Most commonly this is used, for example, in draft documents, where another reader has written notes about the quality of a document at a certain point, "in the margin".

Annotations about bibliographical sources, labeled annotated bibliographies, give descriptions about how each source is useful to an author in constructing a paper or argument. Creating these blurbs, usually a few sentences long, establishes a summary for and expresses the relevance of each source prior to writing.

In computing, the programmer often adds annotations to source code in the form of comments. These do not affect the working of the program but give explanations (for other programmers, or potential readers of the code principally, but also as a reminder for the author), hints or plans for improvement, etc.

Further annotations can also be added by a compiler or programmer in the form of metadata, which is then made available in later stages of building or executing a program. For example, a compiler may use metadata to make decisions about what warnings to issue, or a linker can use metadata to connect multiple object files into a single executable. Differences in computer languages have given rise to a variety of words for programmer-added metadata, including annotation (Java), attribute (C#), pragma (C), and metadata (HTML).

Given that molecular biology and bioinformatics have known the need for DNA annotation since the 1980s, where a previously unknown sequence representation of genetic material is annotated with information relating position to intron-exon-boundaries, regulatory sequences, repeats, gene names and protein products, etc. This annotation is usually stored in predefined fields in biological databases, especially sequence databases. There are a number of very active genomic and proteomic annotation projects today, including Mouse Genome Informatics, FlyBase, and WormBase. Educational materials on some aspects of biological annotation from this year's Gene Ontology annotation camp and similar events are available at the Gene Ontology website.

Imaging

In the digital imaging community the term annotation is commonly used for visible metadata superimposed on an image without changing the underlying raster image, such as sticky notes, virtual laser pointers, circles, arrows, and black-outs (cf. redaction).

Linguistics

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In linguistics, morphological, syntactic, semantic, discourse and pragmatic annotations add information about the linguistic form. Other forms of annotation include comments and metadata; these non-transcriptional annotations are also non-linguistic. A collection of texts with linguistic annotations is known as a corpus (plural corpora).

See also

Look up annotation in Wiktionary, the free dictionary.

• Automatic image annotation
• Marginalia
• Web annotation