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Generalized Markup

The motivation for generalized markup is a departure from that of traditional markup languages. With traditional markup languages, the goal is to add additional information to a document to allow it to be formatted for presentation. The markup is formatting information. With generalized markup, however, the markup is used convey the logical structure of the information. How this structure is formatted should not be the concern of the writer. The provider of the information should only be concerned with providing the important information with the appropriate logical structure. The actual formatting will be performed by systems which will use this information. The logical structure of the information is much more valuable than the way it should be formatted. If the information is structured correctly, a variety of post-processors should be able to use the information which is based on a given tag-set.

So for example a piece of procedural markup might look like:

.TH DF 1V "16 September 1989"
.SH NAME
df \- report free disk space on file systems
.SH SYNOPSIS
.B df

This is a section taken from the df Unix man page. Here, the .TH command sets up the header - the reference page is DF, the section is 1V, and the last field is the date of the most recent change. The .SH command sets up a section heading with the given label, and the .B command displays text in bold. This is relatively typical of procedural markup. While all of the information necessary to present a nicely formatted man page is there, it is all superficial. The sections do not convey the content. The section command is just a section command, and does not convey the fact that the section is the synopsis. In a generalized markup language, SGML in this case, this section of the man page might be represented as:

<man ref=DF sect='1V' date="16 September 1989">
<name> df 
<summary> report free disk space on file systems </summary> 
<synopsis> <com>df</com>

Here the document is labeled as a man page and the <man> attributes ^8.1 are the information that previously generated the header. The name is no longer the text of a section heading; it is labeled as a <name>. The synopsis is labeled as a synopsis, <synopsis>, instead of a section with the heading ``SYNOPSIS''. The ``df'' reference in the synopsis is a command, <com>, instead of a bold section of arbitrary text.

Generalized markup allows the important information to be processed unambiguously by many different systems. With generalized markup, a <synopsis> may be treated as a section for printed text, but for a hypertext system the synopsis may only be displayed if someone presses the synopsis button (however that is done). The information represents a synopsis instead of formatting details. The formatting decisions are left to the discretion of the system which will use the information.

Generalized markup is one tool which will allow information to be reused for a variety of purposes. Once freed from a particular formatting language, many applications can utilize the same information source for many purposes. The same logically structured information can be used to generate a printed manual, a hypertext system, a database, or practically anything else that can be done with information. All that is necessary is that the proper set of tags are defined and processors exist to manipulate information structured with the tags.