Notations provide schema developers with tools for defining their own file and data types. Notations are required for unparsed entities and may be used in attributes as well. Notations are not required for every schema - they provide extra functionality that is dependent on applications for full implementation
Notations, which you can define in the Notation Tab of the Advanced Pane, provide a shorthand description for a resource, typically identified with a system identifier - a URI. (You can also use public identifiers for notations.) Unlike MIME types, commonly used to describe file types for transfer over the Internet, there is no central registry of notations. Every schema can define its own set.
Typically, the SYSTEM identifier of a notation points to a description of the file or data type, and the application can figure out from that identifier how to process the information. Applications that process notations typically need an internal list of identifiers that they can use to cross-reference information described by a notation and the tools for processing it.
For example, the notation image_jpeg might have the system identifier http://www.isi.edu/in-notes/iana/assignments/media-types/image/jpeg
, which points only to a Web page saying 'See RFC 1521.' (RFC 1521 describes the JPEG graphics format.) To show graphics identified with the image_jpeg notation, the application would need to understand that all notation references to http://www.isi.edu/in-notes/iana/assignments/media-types/image/jpeg
identify content that needs to be display in a JPEG viewer.
Notations can also be used to identify data types. XML Authority will display your notations as options for data typing in its Qlicker menus, allowing you to select your notation names as data types. If you use this feature, your application will need to understand how to map your notation declaration's system or public identifier to its own internal data validation schemes.
Note: For a ready-made list of notations describing MIME file types, see John Cowan's MIME Types 2 DTD fragment.
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