An international standard for books, document type definition
, has been created by the International Standards Organization (ISO 12083) and this presents a standardized general markup language (SGML) which has been refined to Extensible Markup Language (XML).
Since SGML documents are not tied to any one vendor or software, various industries have created their own document types (document type definitions
-- DTDs) for information commonly exchanged in their business activities.
Using document type definitions
(DTDs), it allows the promise of self-defining flexibility without sacrificing underlying universality.
(A data set for automotive ads, for example, could include make, model, year and color.) Then the group will develop a document type definition
for using XML, which will "tell the structure of the data and the tags that identify the data," he says.
Others were developed for specialized domains, such as the Text Encoding Initiative (TEI) Guidelines for Electronic Text Encoding and Interchange, including the TEI header as a mandatory element in TEI-conformant texts; the Encoded Archival Description (EAD), an SGML document type definition
for encoding finding aids; and the Content Standards for Digital Geospatial Metadata (CSDGM) developed by the U.S.
Accordingly, a tool was developed to assist with SGML Document Type Definition
In 2009, MISMO first published a sweeping new set of data standards called the Version 3 Reference Model, which is based on XML schema instead of the old document type definition
The combination of the internal subset and the external subset is what you would correctly call the document type definition
. In other words, both portions would form the complete DTD.
HTML, though, has a fixed Document Type Definition
. This is the basis of browser creep -- the tendency of every new browser to have a set of features that doesn't work in any other browser, to the joy of webmasters everywhere.
As a formal language construct, an SGML document can be parsed against a Document Type Definition
(DTD) that unambiguously defines what elements are allowed and where in the document they can (or must) occur.