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CHAPTER 5

FIGURE 5.1
XML Family Tree

linked data, are being used in libraries today, we must first take a step back
and look at XML in general. For many, the definition of what XML means
has become understandably muddled. The definition of XML has been
extended to include not only XML, but the many technologies that have
come out of the XML specification. This is very much like the definition of
MARC today. Like XML, the term “MARC” is often used to represent the
bibliographic descriptive rules and interpretations used to create a MARC
record. MARC21 users equate the MARC field 245 with a title—even though
the MARC specification itself makes no such determination. In part, it’s this
fusion of rules and specification that often makes MARC difficult to work
with outside of the library community. In reality, the MARC format is, at its
most basic, just a container for the data. The Library of Congress developed
MARC as a distribution format that could be used to capture information
from a card catalog in digital form for transfer to other systems. In the
same way, many tend to fold technologies like XSLT, XLink, or XQuery—all
technologies that have been developed out of the XML schema—as part of
the XML definition. While simplistic, figure 5.1 shows an abbreviated ver-
sion of the XML family tree. From the tree, one can see the many different
technologies that have been derived from the XML specification.

XHTML

XHTML marks what many hope will be the next evolution of the HTML
markup language. It was designed as an extension of the HTML4 docu-
ment type which is XML-conforming, meaning that such documents can

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