Transclusion
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In computer science, transclusion is the inclusion of part of a document into another document by reference. Some hypertext systems, including Ted Nelson's Xanadu Project, support transclusion. For example, an article about a country might include a chart or a paragraph describing that country's agricultural exports from a different article about agriculture. Rather than copying the included data and storing it in two places, a transclusion embodies modular design, by allowing it to be stored only once (and perhaps corrected and updated if the link type supported that) and viewed in different contexts. The reference also serves to link both articles.
In Ted Nelson's original proposal for hypertext, outlined in his 1982 book, Literary Machines, micropayments could be automatically exacted from the reader for all the text, no matter how many snippets of content are taken from various places.
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Atomicity requirement
Transclusion works better when sections of text are written atomically, so that sections can stand independently of each other. For example, formulations like "as explained in the previous section", where that previous section is transcluded or transcluding text, are problematic, the section may appear in a different context, causing confusion.
Use in HTML and the Web
Present HTML has a limited form of transclusion. A page can transclude an image, as well as another document by including inline frames (called "iframe"); see inline linking. The web browser retrieves the inline content and draws it on the page. As of January 2002, Weather.com was using this technique to build its weather forecast page from several small documents.
Future versions of HTML may support deeper transclusion of portions of documents using XML technologies such as XPath's document referencing and XSLT manipulations. See also Framing in websites.
The practice of 'remote loading', including data from other sites, such as links to images, etc., is usually frowned upon because of the use of bandwidth (even called "bandwidth theft") and computing power required from the remote computer system. This is said to "tax" another server, and is often considered an example of leeching.
A major exception to this rule is web advertising, where advertisements supplied by an advertiser are published with other content by a publisher. An advertiser prefers to serve an advertisement and be able to detect when it was viewed, rather than have it served by the publisher and have to trust the publisher. (See also: hit counter, web bug).
Use in other technologies
There are other technologies that have similar abilities of including external components such as ASP (Active Server Pages), JSP (JavaServer Pages), PHP (originally Personal Home Page, now PHP Hypertext Preprocessor), and the use of SSI (Server Side Includes).
The term "transclusion" is an example of a portmanteau combining, presumably transfer and inclusion.
See also
- Compound document
- Single source publishing
- PurpleWiki [1] is a UseModWiki derivative that implements TransClusion using Purple Numbers.
- The Linux-HA project uses wiki transclusion to create its public web site.
- Wikipedia:Transclusion, transclusion in Wikipediaes:Transclusión