Datasheet

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Part I ✦ Introducing XML
XML markup also makes it easier for nonhuman automated computer software to
locate all of the songs in the document. A computer program reading HTML can’t
tell more than that an element is a
DT. It cannot determine whether that DT repre-
sents a song title, a definition, or some designer’s favorite means of indenting text.
In fact, a single document might well contain
DT elements with all three meanings.
XML element names can be chosen such that they have extra meaning in additional
contexts. For example, they might be the field names of a database. XML is far more
flexible and amenable to varied uses than HTML because a limited number of tags
don’t have to serve many different purposes. XML offers an infinite number of tags
to fill an infinite number of needs.
Why Are Developers Excited About XML?
XML makes easy many web-development tasks that are extremely difficult with
HTML, and it makes tasks that are impossible with HTML possible. Because XML is
extensible, developers like it for many reasons. Which reasons most interest you
depends on your individual needs, but once you learn XML, you’re likely to discover
that it’s the solution to more than one problem you’re already struggling with. This
section investigates some of the generic uses of XML that excite developers. In
Chapter 2, you’ll see some of the specific applications that have already been devel-
oped with XML.
Domain-specific markup languages
XML enables individual professions (for example, music, chemistry, human
resources) to develop their own domain-specific markup languages. Domain-specific
markup languages enable practitioners in the field to trade notes, data, and informa-
tion without worrying about whether or not the person on the receiving end has the
particular proprietary payware that was used to create the data. They can even send
documents to people outside the profession with a reasonable confidence that those
who receive them will at least be able to view the documents.
Furthermore, creating separate markup languages for different domains does not
lead to bloatware or unnecessary complexity for those outside the profession. You
may not be interested in electrical engineering diagrams, but electrical engineers are.
You may not need to include sheet music in your web pages, but composers do. XML
lets the electrical engineers describe their circuits and the composers notate their
scores, mostly without stepping on each other’s toes. Neither field needs special
support from browser manufacturers or complicated plug-ins, as is true today.
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