In computer science, some Hypertext systems, including Ted Nelson s Project Xanadu, have the capability for documents to include sections of other documents by reference, called 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 allows 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 would be automatically exacted from the reader for all the text, no matter how many snippets of content are taken from various places.

=Atomism=

The idea of transclusion implies that sections of text can be written atomism, so that the content of one section does not interfere with the contents of another section. For example, the following formulations, often found in written linear prose, are not possible:

As one does not know where the section will appear, one cannot reference text outside the section in this manner, as one does not know if it will be there or not. If someone else chooses to use the section elsewhere, it will be confusing.

For some kinds of prose, these kinds of limitations are not severe, but to others it may be disturbing and lower the quality of the text.

=HTML / web usage=

Present HTML has a limited form of transclusion. For instance, it is possible to refer to an image, which the web browser will retrieve and draw on the page; see inline linking.

Also, an HTML document can contain an iframe, or inline frame, that refers to another document and presents it as text inside the calling document. .

Certain implementations of Wiki software support a form of transclusion. On sites created using TiddlyWiki, for example, text is presented in the form of microcontent which is loaded into the main display when the user clicks on wikilinks.

The practice of remote loading , including data from other sites, such as links to images, etc., is something 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 bandwidth theft.

However, there is one major exception to this rule: web ).

=A side note=

There are other technologies that have similar abilities of including external components such as Active Server Pages (Active Server Pages), JavaServer Pages (JavaServer Pages), PHP (originally Personal Home Page, now PHP Hypertext Preprocessor), and the use of Server Side Includes (Server Side Includes).

=See also=