Everything You Ever Wanted to Know About DTDs,
		But Were Afraid to Ask
	
		     Arnaud Sahuguet
		University of Pennsylvania
	
For the last two years, XML has become an increasingly popular
data-format embraced by a lot of different communities. XML is
extremely attractive because it offers a simple, intuitive and uniform
text-based syntax and is extensible.
One can find today XML proposals for messages, text content delivery
and presentation, data content, documents, software components,
scientific data, real-estate ads, financial products, cooking recipes,
etc.
Unfortunately this also means that XML is far too general and if
people plan to use it in serious applications (mainly for Electronic
Document Interchange, in a broad sense), they will need to provide a
specification (i.e. structure, constraints, etc.) for their XML,
which XML itself cannot offer.
In order to specify and enforce this structure, people have been using
Document Type Definitions (DTDs), inherited from SGML.

In this paper, we present some preliminary results that explore how
DTDs are being used for specifying the structure of XML documents. By
looking at some publicly available DTDs, we look at how people are
actually (mis)using DTDs, show some shortcomings, list some
requirements and discuss possible replacements.