Transclusion

In computer science, transclusion is the inclusion of part of a document into another document by reference. It is a feature of substitution templates.

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.

Nelson coined the term "transclusion," as well as "hypertext" and "hypermedia", in his 1982 book, "Literary Machines". Part of his proposal was the idea that micropayments could be automatically exacted from the reader for all the text, no matter how many snippets of content are taken from various places.

Nelson has recently delivered a demonstration of Web transclusion, the Little Transquoter (programmed to Nelson's specification by Andrew Pam). It creates a new format built on portion addresses from Web pages; when dereferenced, each portion on the resulting page remains click-connected to its original context—always a key aspect of transclusion for Nelson, but missing in most implementations of transclusion.

Technical considerations

Context neutrality

Transclusion works better when transcluded sections of text are self-contained, so that the meaning and validity of the text is independent of the context in which it appears. For example, formulations like "as explained in the previous section" are problematic, because the transcluded section may appear in a different context, causing confusion. What constitutes "context neutral" text varies, but often includes things like company information or boilerplate.

Parameterization

Under some circumstances, and in some technical contexts, transcluded sections of text may not require strict adherence to the "context neutrality" principle, because the transcluded sections are capable of "parameterization". Parameterization implies the ability to modify certain portions or subsections of a transcluded text depending on exogenous variables that can be changed independently. This is customarily done by supplying a transcluded text with one or more "substitution placeholders". These placeholders are then replaced with the corresponding variable values prior to rendering the final transcluded output in context.

Use on the Web

HTML

At present, transclusion in HTML is somewhat limited by lack of standards support in Internet Explorer. Although all graphical browsers can transclude an image, including a document is a bit more difficult. There are currently two methods of achieving this result:

*The IFrame (inline frame) element, which includes whole documents.
*The Object element. In Firefox and other browsers, this allows true document transclusion, enabling one page to be built from several smaller documents.

In addition, Ajax can achieve a similar result across all modern, JavaScript-enabled browsers.

Future versions of HTML may support deeper transclusion of portions of documents using XML technologies such as entities, XPointer document referencing, and XSLT manipulations. (XPointer is patent-encumbered.)

The practice of 'remote loading'—including data, such as images, directly from other sites—is usually frowned upon because of the use of bandwidth and computing power required from the remote computer system (see Bandwidth theft). This is said to "tax" another server, and is often considered an example of leeching. Increased distribution of proxy servers has the potential to turn this around and take advantage of transclusion to reduce redundant transmissions of the same data.

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).

Mashups are a recent phenomenon similar to transclusion.

erver-side Transclusion

Transclusion can also be accomplished on the server side, provided the server software includes this functionality. This can be done through multiple different technologies, including Server Side Includes and markup entity references resolved by the server software. Client-side transclusion is generally preferable as data transcluded into several pages can be cached by the client rather than sent out again for every page.

Publications

* cite conference
last = Di Iorio
first = A.
authorlink =
coauthors = Vitali, F.
title = A Xanalogical Collaborative Editing Environment
booktitle = Proceedings of the Second International Workshop of Web Document Analysis 2003 (WDA2003)
month = August | year = 2003
location = Edinburgh, UK
url = http://www.csc.liv.ac.uk/~wda2003/Papers/Section_III/Paper_11.pdf
format = PDF

* cite journal
last = Kolbitsch
first = J.
authorlink =
coauthors = Maurer, H.
title = Transclusions in an HTML-Based Environment
journal = Journal of Computing and Information Technology
volume = 14
issue = 2
pages = 161–174
month = June | year = 2006
url = http://cit.zesoi.fer.hr/browseIssue.php?issue=25
doi = 10.2498/cit.2006.02.07

* cite journal
last = Kolbitsch
first = J.
authorlink =
coauthors =
title = Fine-Grained Transclusions of Multimedia Documents in HTML
journal = Journal of Universal Computer Science
volume = 11
issue = 6
pages =
publisher =
month = June | year = 2005
url = http://www.jucs.org/jucs_11_6/fine_grained_transclusions_of/
doi =
id =
accessdate =

* cite conference
first = H.
last = Krottmaier
authorlink =
title = Transcluded Documents: Advantages of Reusing Document Fragments
booktitle = Proceedings of the 6th International ICCC/IFIP Conference on Electronic Publishing (ELPUB2002)
pages = 359–367
publisher = Karlovy Vary
year = 2002
location = Czech Republic
url = http://hkrott.iicm.edu/docs/publications/elpub-2002.pdf
format = PDF

* cite conference
first = H.
last = Krottmaier
authorlink =
coauthors = Helic, D.
title = Issues of Transclusions
booktitle = Proceedings of the World Conference on E-Learning in Corporate, Government, Healthcare, & Higher Education (E-Learn 2002)
pages = 1730–1733
year = 2002
location = Montreal, Canada
url = http://coronet.iicm.edu/denis/pubs/elearn2002b.pdf
format = PDF

* cite journal
last = Krottmaier
first = H.
authorlink =
coauthors = Maurer, H.
title = Transclusions in the 21st Century
journal = Journal of Universal Computer Science
volume = 7
issue = 12
pages = 1125–1136
publisher =
month = July | year = 2001
url = http://www.jucs.org/jucs_7_12/transclusions_in_the_21st/
doi =
id =
accessdate =
format = PDF, HTML, PostScript

* cite conference
first = A.
last = Moore
authorlink =
coauthors = "et al"
title = Personally tailored teaching in WHURLE using conditional translucion
booktitle = Proceedings of the Twelfth ACM Conference on Hypertext and Hypermedia
pages = 163–164
publisher =
year = 2001
location = Aarhus, Danmark
url =
doi =
id =
accessdate =

* cite book
last = Nelson
first = T. H.
authorlink =
coauthors =
title = Literary Machines
publisher = Mindful Press
year = 1981

* cite journal
first = T. H.
last = Nelson
authorlink =
coauthors =
title = The Heart of Connection: Hypermedia Unified by Transclusion
journal = Communications of the ACM
pages = 31–33
issue = 8
year = 1995
location =
url =
doi =
id =
accessdate =

* cite web
last = Nelson
first = T. H.
title = Generalized Links, Micropayment and Transcopyright
year = 1996
url = http://www.almaden.ibm.com/almaden/npuc97/1996/tnelson.htm
publisher = Almaden Research Center

* cite web
last = Nelson
first = T. H.
title = Transcopyright: Pre-Permission for Virtual Republishing
year = 1998
url = http://www.aus.xanadu.com/xanadu/transcopy.html

* cite journal
last = Nelson
first = T. H.
authorlink =
coauthors =
title = Xanalogical Structure, Needed Now More than Ever: Parallel Documents, Deep Links to Content, Deep Versioning and Deep Re-Use
journal = ACM Computing Surveys
volume =
issue = 4es
pages =
publisher =
year = 1999
url = http://xanadu.com.au/ted/XUsurvey/xuDation.html
doi =
id =
accessdate =

* cite web
last = Pam
first = A.
title = Fine-Grained Transclusion in the Hypertext Markup Language
work = Internet Draft
year = 1997
url = http://xanadu.com.au/archive/draft-pam-html-fine-trans-00.txt
format = Text

* cite book
last = Wilde
first = E.
authorlink =
coauthors = Lowe, D.
chapter = XML Linking Language
title = XPath, XLink, XPointer, and XML: A Practical Guide to Web Hyperlinking and Transclusion
publisher = Addison-Wesley Professional
year = 2002
location =
pages = 169-198
chapterurl = http://searchwebservices.techtarget.com/searchWebServices/downloads/wilde-lowe_07.pdf
format = PDF

External links

* [http://www.xanadu.com.au/transquoter/ The Little Transquoter]

ee also

* Compound document
* Macro
* Single source publishing
* Subroutine
* Cross-reference