xml uses and books to read

[Richard Gaskin]

Graham Samuel wrote:
> On Sun, 11 Apr 2004 18:10:15 -0700, Richard Gaskin 
> <ambassador at fourthworld.com> wrote:
> 
>> [...]
>> XML is just data given structure by putting it between starting and
>> ending tags.  Though an increasing number of applications use it for
>> data storage, its primary benefit is in exchanging data with other apps.
>>
>> So once you find a task for which XML would be a good way to exchange
>> data, find out which tags the others apps use and parse those out to get
>> the data you're after.
> 
> 
> Richard, you are the king of commonsense! This simple idea has made me 
> more aware of the **idea** of XML than many another text I have had the 
> misfortune to read.
> 
> The other bit of info about the **principles**  of XML that is missing 
> for me is the answer to the question:
> 
> "If XML tags and structures can be made to represent pretty well 
> anything, how does the user community for a particular dialect/ 
> language/ data model expressed in XML communicate? I mean, if a 
> particular set of XML tags and structures is about chemical compounds or 
> the parts of a bicycle or whatever, is there a generalised 
> metalinguistic way of defining what the representation means, or does 
> the community share some more or less informal description and then 
> conform to that?"

This is commonly done through a DTD, or "document type declaration", and 
is often the second line in an XML file (the first being the XML 
declaration).

For example, here are the first two lines from Rev's info.plist file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" 
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">

The first line describes the XML version used, and the second provides 
the location of the DTD that defines the type of XML document it is.

For more on DTDs see:
<http://www.w3.org/TR/2004/REC-xml-20040204/#dt-doctype>

The annotated version is likely more helpful:
<http://www.xml.com/axml/axml.html>

This discussion on type declarations is quite readable, if a little sparse:
<http://www.rpbourret.com/xml/xmldtd.htm>

There are many more good references and tutorials:
<http://www.google.com/search?q=declaring+xml+doctype&btnG=Search>

-- 
  Richard Gaskin
  Fourth World Media Corporation
  ___________________________________________________________
  Ambassador at FourthWorld.com       http://www.FourthWorld.com