SGML and VRML

[Alexander Von_obert <avobert -at- TWH -dot- MSN -dot- SUB -dot- ORG>]

Hello Nancy,


* Antwort auf eine Nachricht von Nancy Hayes an All am 15.01.96

NH> As I understand it, the advantage to SMGL is in the use of
NH> style sheets.

SGML is quite some abstract standard. There is one thing you can do with SGML:
 Tag your document according to its contents. What you mean by "style sheet" is
 called "Document Type Definition" (DTD). SGML does not offer a DTD but
 describes a way to define a DTD and a way to express your documents according
 to the structure from the DTD.

NH> I =think= if the company adapted a new format, that all they
NH> would have
NH> to do is change the style sheet--instead of recode the old
NH> documents.

You would have to rewrite the DTD and write a filter (UNIX terminology: a
 program that receives a data stream and produces a data stream from it) to
 convert the old data structure to the new one. Most lokely this will be a
 database application.

Or, if your changes are only some layout changes, you do not do anything with
 your SGML document. The SGML document by itself contains absolutely *no*
layout
 information.

NH> I also think SMGL accepts greek, math, and tables more
NH> effectively than HTML.

HTML is something like a SGML system using a fixed DTD. SGML describes ways to
 extend your character sets, e.g. an a umlaut is expressed as &aauml; and there
 are no code pages like you know from many systems (including Unicode).

SGML enables you to represent your documents according to their contents. If
 you wish to, you can write a DTD segment describing the structure of some kind
 of table or what you like. But you will not necessarily see a table while you
 write the document. If you get some WYSIWYG SGML editor, someone invested LOTS
 of time to give you some idea of the final look of your document. But the
 output processor may change that layout if its programmer thinks he needs to.

NH> information on VRML

This quite some different kind of mouse than SGML :-)


Greetings from Germany,
Alexander

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