Interchange Model. Exif is a standard that specifies the image and audio file formats used by digital cameras, including some metadata tags. TagSpaces is an open-source cross-platform application for tagging files; it inserts tags into the filename. For an event An official tag is a keyword adopted by events and conferences for participants to use in their web publications, such as blog entries, photos of the event, and presentation slides. Search engines can then index them to make relevant materials related to the event searchable in a uniform way. In this case, the tag is part of a controlled vocabulary. In research A researcher may work with a large collection of items (e.g. press quotes, a bibliography, images) in digital form. If he/she wishes to associate each with a small number of themes (e.g. to chapters of a book, or to sub-themes of the overall subject), then a group of tags for these themes can be attached to each of the items in the larger collection. In this way, freeform classification allows the author to manage what would otherwise be unwieldy amounts of information. Special types Triple tags A triple tag or machine tag uses a special syntax to define extra semantic information about the tag, making it easier or more meaningful for interpretation by a computer program. Triple tags comprise three parts: a namespace, a predicate, and a value. For example, geo:long=50.123456 is a tag for the geographical longitude coordinate whose value is 50.123456. This triple structure is similar to the Resource Description Framework model for information. The triple tag format was first devised for geolicious in November 2004, to map Delicious bookmarks, and gained wider acceptance after its adoption by Mappr and GeoBloggers to map Flickr photos. In January 2007, Aaron Straup Cope at Flickr introduced the term machine tag as an alternative name for the triple tag, adding some questions and answers on purpose, syntax, and use. Specialized metadata for geographical identification is known as geotagging; machine tags are also used for other purposes, such as identifying photos taken at a specific event or naming species using binomial nomenclature. Hashtags A hashtag is a kind of metadata tag marked by the prefix #, sometimes known as a "hash" symbol. This form of tagging is used on microblogging and social networking services such as Twitter, Facebook, Google+, VK and Instagram. The hash is used to distinguish tag text,