Separation of presentation and content

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Separation of presentation and content (or "separate content from presentation") is a common idiom, a design philosophy, and a methodology applied in the context of various publishing technology disciplines, including information retrieval, template processing, web design, web development, word processing, desktop publishing, and model-driven development. It is a specific instance of the more general philosophy, separation of concerns.

[edit] Intended meaning

When invoked as an idiom, the underlying concept is to make a distinction between the actual meaning of a document, and how this meaning is presented to its readers. A common example is the em element in HTML, to denote emphasis. Which is part of the content of the document, its presentation may be printing it in an oblique rendering. However since emphasis in a text that is already oblique should in fact be printed normal again or in boldface, and since other texts can also be oblique. Separation of content and presentation marks all those things differently, even though they can be presented in the same way, or marks them identical, and presents them differently.^[1]

An extreme example of separation of presentation and content—a list presented as a tag cloud.

[edit] Machine readability

The general aim of separation of presentation and content is machine readability, that is, making it possible for machines to detect meaning or intent. The machine readability is then a means to desired ends (discussed below). For example, a human being reading a document has little trouble to grab from context that an oblique rendering in one place would be emphasized text, but in another place is a title of a book. However, as robots and crawlers have more difficulty with this task, separation of presentation and content generally aids in their distinguishing of such things which are presented in the same way, but have a different meaning—or have the same meaning, but are presented in a different way.

The highest-level abstraction of the goals served by machine readability is "to increase quality of life", which requires "affordably serving the information to a wider variety of users [in a presentation that they can understand]", whether for the purpose of fairness, that is, to increase quality of life for others (where the users include humans with disabilities or humans who are poor); for the purpose of wealth creation, that is, to increase quality of life for oneself (where the users are typically machines that can do things that humans cannot do, and are serving in the creation of wealth); or for both purposes synergistically (where increasing the quality of life of other humans makes them more productive, so that they add to the wealth creation). To serve these highest-level goals requires the ability to recast abstractions in new instances quickly and cheaply (that is, without time-consuming reworking), which generally requires automation rather than person-hours of labor. For example:

• The ability to deliver the same information in different media, and to change the medium quickly and cheaply; and within one medium, to change instances easily
  • To serve the same message to different users:
    • as printed display (for technophobes or for users with contextual desire for print)
      • as printed display typeset in various graphic designs
    • as online visual display (for most users in most instances)
      • as online visual display in various graphic designs
    • as online audio (for blind users or for sighted users with contextual desire for audio)
    • as braille (for blind users)
    • as input to an API (for users that are machines)
      • The other machines can then take the information and do further transformations or actions. These may be ones that people cannot do (or cannot do quickly and cheaply), but machines can do (and can do [more] quickly and [more] cheaply). For example:
        • Take a book and gist-translate it into another natural language
        • Take audio of speech and gist-translate it into another natural language
        • Take audio of speech and transcribe it for reading (for deaf users or for hearing users who want transcription of voicemail into e-mail or IM)
        • Take the data contained in an entire library and search through it for ABC-XYZ, then turn every instance of ABC blue, and serve every instance of XYZ to a machine that will categorize it

[edit] Common terms

There are a number of common terms used to describe these two separate dimensions of communication, which include:

Semantic 

logic, information, ontology, semantics, data, outline, model, message, content

Aesthetic (or parsing-related)

graphics, design, layout, style, visualization, view, medium, presentation

[edit] Possibility and degrees of separation

In communication design, the message is the content and the medium is the tools to deliver that message. In the book Understanding Media, Marshall McLuhan stated that "The medium is the message", which has since been the subject of much debate. One interpretation is that the choice of medium (presentation tools) affects the (presentation content) message. It is possible for the choice of content and choice of medium to affect the quality of the presentation, meaning how well a message may be received. The degree that content may be separated from presentation depends on how much the quality of the medium effects the quality of the message. In many cases, the possibility and degrees of separation are as subjective as the content itself.

[edit] See also

• Separation of concerns
• Templates
• Style sheet (web development)
• Style sheet (desktop publishing)
• Template systems
• What You See Is What You Mean
• Internationalization^[2]
• model-view-controller

[edit] References

1. ^ http://www.webreference.com/html/tutorial5/1.html
2. ^ Research and Advanced Technology for Digital Libraries: Second European Conference, Ecdl '98 by Christos Nikolaou, Constantine Stephanidis - 1998 - 911 pages

[edit] External links

• CSS Zen Garden: A site which challenges designers to create new page layouts without touching the XHTML source. Includes dozens of layouts. CSS source can be viewed for every layout.