Sidecar file
Encyclopedia
Sidecar files, also known as buddy files or connected files, are files which store data (often metadata
) which is not supported by the source file format.
For each source file one or more sidecar files can be created. This is in contrast to "metadata databases" where one database contains metadata for several source files.
In most cases the relationship between the source file and the sidecar file is based on the file name; sidecar files have the same base name as the source file, but with a different extension. The problem with this system is that most operating systems and file managers have no knowledge of these relationships, and might allow the user to rename or move one of the files thereby breaking the relationship.
A variation of this are copies of the source file which contain largely the same information, but in a different format or from a previous version:
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
) which is not supported by the source file format.
For each source file one or more sidecar files can be created. This is in contrast to "metadata databases" where one database contains metadata for several source files.
In most cases the relationship between the source file and the sidecar file is based on the file name; sidecar files have the same base name as the source file, but with a different extension. The problem with this system is that most operating systems and file managers have no knowledge of these relationships, and might allow the user to rename or move one of the files thereby breaking the relationship.
Examples
Various examples of sidecar files are:- AmigaOS .info files.
- XMPExtensible Metadata PlatformThe Adobe Extensible Metadata Platform is a standard, created by Adobe Systems Inc., for processing and storing standardized and proprietary information relating to the contents of a file....
sidecar files. For file formats that have no internal support for XMP data, the data is stored in separate .xmp files with the same base file name. Many photo cataloging applications have support for this file format. - Windows connected files. When an HTML document is written to a local disk, all images, stylesheets and other connected resources are stored inside a subfolder that has the base name of the source HTML file with "_files" added. Windows ExplorerWindows ExplorerThis article is about the Windows file system browser. For the similarly named web browser, see Internet ExplorerWindows Explorer is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface...
will move or delete all files when either the source HTML file or the folder is moved or deleted. Applications that support this format are Windows ExplorerWindows ExplorerThis article is about the Windows file system browser. For the similarly named web browser, see Internet ExplorerWindows Explorer is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface...
, Internet ExplorerInternet ExplorerWindows Internet Explorer is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems, starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year...
and Microsoft WordMicrosoft WordMicrosoft Word is a word processor designed by Microsoft. It was first released in 1983 under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platforms including IBM PCs running DOS , the Apple Macintosh , the AT&T Unix PC , Atari ST , SCO UNIX,...
. - AVI + THM. Many digital cameras will store a .thm (thumbnail) file alongside recorded movies, with the same base filename as the movie file. These thumbnail files are plain JPEGJPEGIn computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
files with another extension. This system allows for quickly displaying a still preview of the movie, and storing camera data which is not supported by the AVI file format. - JPEG + WAV. Some digital cameras allow for voice/audio annotations with photos. These are then stored as WAVWAVWaveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
audio files alongside the JPEGJPEGIn computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
photo file, with the same base filename. - Mac OS resource forkResource forkThe resource fork is a construct of the Mac OS operating system used to store structured data in a file, alongside unstructured data stored within the data fork. A resource fork stores information in a specific form, such as icons, the shapes of windows, definitions of menus and their contents, and...
. The Mac OSMac OSMac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
operating system has internal support for metadata/resources that are not stored inside the file data. Because the support is built into the operating system, these resource forks will not show up as separate files, and all applications inherit support for resource forks. However, when files with a resource fork are copied over to a non-Mac OS disk format, such as an ISO-format CD-ROMCD-ROMA CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....
or a MS-DOSMS-DOSMS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
compatible disk, this resource fork will be stored as a separate file alongside the main source file. - Meta Information Encapsulation sidecar files. The MIE format is an extensible, dedicated meta information format part of ExifToolExifToolExifTool is a free software program for reading, writing, and manipulating image, audio, and video metadata. It is platform independent, available as both a Perl library and command-line application...
. MIE files can be used to encapsulate meta information from many sources and bundle it together with any type of file.
A variation of this are copies of the source file which contain largely the same information, but in a different format or from a previous version:
- Backup and versioning files; many applications create backup files alongside the main file, often with a .bak extension.
- .exf backup files. Since many JPEGJPEGIn computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
editing software used to destroy Exif metadata stored in digital photos, some photo cataloging applications allow to extract the Exif data and store that in an .exf file, so that the metadata can later be re-inserted into the JPEG file. - Raw + JPEG. Many digital cameras allow to store both uncompressed rawRAW image formatA camera raw image file contains minimally processed data from the image sensor of either a digital camera, image scanner, or motion picture film scanner. Raw files are so named because they are not yet processed and therefore are not ready to be printed or edited with a bitmap graphics editor...
data and a JPEGJPEGIn computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
image file when shooting in "raw mode". This allows for faster previewing the photo, and support by applications that do not support the (often undocumented) raw format.