Incomputing, afile association associates a file with anapplication capable of opening that file. More commonly, a file association associates a class of files (usually determined by theirfilename extension, such as.txt) with a corresponding application (such as atext editor).
A single file extension may have several associations for performing various actions, also known asverbs. Some of the common verbs are:
Apicture, for example, may be associated with these words so thatopen opens the picture in animage viewer,edit opens up animage editing program andprint sends the picture to a printer.
Mostoperating systems support file associations in some form or the other. For example, opening a file from a file manager usually invokes theopen verb in order to open the file with its associated application. The "open" verb invokes the associatedapplication program, which reads the file or document and presents it to the user for viewing, and possibly for editing or other action.
Additional actions such asprint are usually accessed via a right-clickcontext menu. A mechanism for modifying associations is also usually present. An example for this is theOpen With option in theWindows Shell.
TheMicrosoft Windows series ofoperating systems, beginning withWindows 3.x supports file extension-based associations.[1] Associations are stored inregistry[2] as sets of verbs for each file extension. Older versions supportedopen associations stored inWIN.INI.File associations can be displayed and edited using theassoccommand and with the help of theftype command it is possible to create association between file type and application which will open files of this type.[3][4]
The Windows shell invokes file association actions throughCOM, drag and drop, command line calls or throughDynamic Data Exchange. Advanced features of Microsoft Windows file associations included manually defining a new file extension with any number of associated actions, a primarydefault action, showing extensions only for specific file types, customizing the file type icon and description and customizing associatedMIME type and their handling (how to handle file types for files downloaded or directly opened from within theInternet Explorer browser). The ability to configure advanced file association functionality, however, was removed inWindows Vista and later operating systems.
Linux-based GUIs, such asKDE andGNOME, supportMIME type-based associations.[citation needed] For example, the MIME typetext/plain would be associated with atext editor. This association is generally accomplished through thefreedesktop.org Shared MIME database (for determining the MIME type of a file) and theDesktop Entry specification (for determining which application to open the file with).[5]
TheClassic Mac OS usedtype codes andcreator codes to associate each file with its corresponding application, regardless of file extension. The more recentmacOS also supports file extension–based associations.
Application bundles in macOS declare supported file types in their Info.plist file. For each of these specified types, aUniform Type Identifier is given, along with a list of 'tags' which define how a file or data of this type could be identified. For example, theJPEG type is defined with a UTI of 'public.jpeg', and tagged with the extensions 'jpg' and 'jpeg', theMIME type 'image/jpeg' and thetype code 'JPEG'.[6]
The operating system uses this information to generate a list of applications which are able to open each type. WithinFinder (software) each file will be identified with a UTI and open with the default application for that type. The user may also select from a list of other applications which support the type.
Using this system, types are also associated with data for which there is no file name or the file extension is missing. This includes pasteboard data and data streaming over a protocol such asHTTP where a MIME type has been given.
assocftype