XML schema languages: beyond DTD
| Pages | 9-15 |
| Published date | 01 March 2000 |
| DOI | https://doi.org/10.1108/07378830010314366 |
| Date | 01 March 2000 |
| Author | Demetrios Ioannides |
| Subject Matter | Information & knowledge management,Library & information science |
XML schema languages:
beyond DTD
Demetrios Ioannides
Introduction
Markup languages have existed since the early
1960s in various incarnations. Yet no concerted
effort to make a markup language standard the
foundation of mainstream computer
applications had been undertaken until
recently. IBM's generalized markup language
evolved into SGML by the late 1970s, and to
the ISI 8879 standard by the mid-1980s
(``Extensible...'', 1998). However, SGML
never found much application beyond the
publishing industry and a few government and
academic projects. When HTML took the
world by storm in the early 1990s the need of a
standard document/data format was
immediately recognized. HTML could offer
nothing more than a simplistic document
rendition, while SGML was too awkward to be
used with emerging tools.
XML 1.0 was endorsed as a World Wide Web
Consortium Recommendation in February of
1998. It had already made headlines in
mainstream computer publications in 1997,
when Microsoft, Netscape, and others revealed
their intention to make XML an important part
of their strategic planning (Radosevich, 1 and
15 September 1997). XML was introduced as a
subset of SGML, and, according to the
recommendation, its ``goal is to enable generic
SGML to be served, received, and processed on
the Web''. In less than two years, XML has
attracted more attention and spurred more
creative activity and enthusiasm than SGML
did in 20 years.
The complexity of SGML was not so much
due to the tagging itself. It was the result of the
awkwardness of the document type definitions
(DTDs). The DTD is the way by which the
SGML document structure rules are defined. It
contains a number of declarations of elements,
attributes, and entities and it defines a
document's hierarchy and granularity. It is no
wonder that the DTD and its contents were
from the beginning the primary target for
simplifications. W3C has published a list of
such modifications[1]. Attempts to automate
the conversion from SGML DTD to XML
DTD are under way. Bob DuCharme
demonstrates some of the benefits and
problems of utilizing scripts written in PERL or
other scripting languages in order to
The author
Demetrios Ioannides is based at the Michigan State
University, East Lansing, MI, USA. ioannide@msu.edu
Keywords
Information technology, Computer languages
Abstract
The flexibility and extensibility of XML have largely
contributed to its wide acceptance beyond the traditional
realm of SGML. Yet, there is still one more obstacle to be
overcome before XML is able to become the evangelized
universal data/document format. The obstacle is posed by
the limitations of the legacy standard for constraining the
contents of an XML document. The traditionally used DTD
(document type definition) format does not lend itself to be
used in the wide variety of applications XML is capable of
handling. The World Wide Web Consortium (W3C) has
charged the XML schema working group with the task of
developing a schema language to replace DTD. This XML
schema language is evolving based on early drafts of XML
schema languages. Each one of these early efforts adopted a
slightly different approach, but all of them were moving in
the same direction.
Electronic access
The current issue and full text archive of this journal is
available at
http://www.emerald-library.com
XML and electronic
publishing
9
Library Hi Tech
Volume 18 .Number 1 .2000 .pp. 9±14
#MCB University Press .ISSN 0737-8831
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