background image
The XML Family
of Technologies
52
XML and Databases
A frequent entry in XML FAQ lists is `Is XML a database?'The answer is almost always
a straight and unequivocal `no', but the regularity with which the question is posed sug-
gests that the connections may be stronger than we may previously have thought. XML
is certainly more powerful when coupled with a database, and the ongoing shift towards
database-driven Web pages mirrors the rise of XML almost inseparably. In his ongoing
exploration of the relations between these increasingly influential technologies, Ronald
Bourret outlines the case thus:
On the plus side, XML provides many of the things found in databases: storage
(XML documents), schemas (DTDs, XML schema languages), query languages
(XQuery, XPath, XQL, XML-QL, QUILT, etc.), programming interfaces (SAX, DOM,
JDOM), and so on. On the minus side, it lacks many of the things found in real
databases: efficient storage, indexes, security, transactions and data integrity, multi-user
access, triggers, queries across multiple documents, and so on.
57
XPath is the XML technology most frequently used for querying XML documents,
and it can be considered analogous to the Structured Query Language (SQL) with which
all modern databases can be interrogated, and indeed defined. XML can assist in ensuring
the longevity of data as proprietary formatting is not used, hence migrating data between
platforms is simplified.
58
Data durability concerns all information technology sectors, and
the cultural heritage sector cannot afford to lag behind.
Towards an Interoperable Semantic Web?
`The Semantic Web is an extension of the current web in which information is given well-defined
meaning, better enabling computers and people to work in cooperation.' Tim Berners-Lee, James
Hendler, Ora Lassila, "The Semantic Web", Scientific American, May 2001
59
The concept of a Semantic Web was introduced by WWW creator Tim Berners-Lee in
1998. At that time,Web content had recently begun the significant shift from what the W3C
calls `exclusively human-oriented content', best exemplified by simple, manually created
HTML pages, to complex and dynamic Web sites built on top of underlying databases.
The Semantic Web depends on the definition and linkage of data in ways that facilitate
efficient, automated resource discovery, the automation of Web tasks and services, as well as
compatibility, reuse, and repurposing across different platforms and software applications.
60
57
Ronald Bourret,"XML and Databases", available online at http://www.rpbourret.com/xml/XMLAndDatabases.htm
58
See http://www.naa.gov.au/recordkeeping/preservation/digital/xml_data_formats.html for more on XML
and data migration.
59
http://www.scientificamerican.com/article.cfm?articleID=00048144-10D2-1C70-84A9809EC588EF21&catID=2
60
For further analysis of the Semantic Web, and in particular its implications for the cultural and scientific
heritage communities, see our third Thematic Issue, entitled "Towards a Semantic Web for Heritage
Resources", available online at http://www.digicult.info/pages/publications.php. A good introduction to
the potential and challenges of this growing topic is given by Shiyong Lu, Ming Dong and Farshad Fotouhi
in their paper "The Semantic Web: opportunities and challenges for next-generation Web applications",
Information Research, vol. 7, no. 4, July 2002: http://informationr.net/ir/7-4/paper134.html
TWR2004_01_layout#62 14.04.2004 14:07 Uhr Seite 52