"Exploring" the Tree
December 21, 1998
Programmatic access to XML essentially allows you to
climb the tree, modify values of its nodes, and collect
node values for processing and/or output. Other technologies
for accomplishing these tasks are also percolating:
XSL
is a style sheet and transformation language
which could be used to prepare XML documents for output and,
to a certain extent, process them. Proposals for query
languages, such as
XQL and
XML-QL,
may offer discrete technologies for culling
data from an XML document. In any case, our focus today
is on programmatic Document Object Model access to the
XML tree.
The utility, then, of access to the XML document via
the DOM is wide open and varied. Recalling the petfolio
example, we can imagine several simple possibilities:
1. Queries of the XML data. An inquisitive user might request
to see only the names of all pets in the petfolio.
By traversing the XML tree, your program code could retrieve
these names and return them as an output list.
2. Processing the XML data. An actuarial user might wish to
find the mean age of pets in the petfolio. Your
program could climb through the XML tree, retrieve the
age values for each pet, perform the necessary calculations,
and output the result.
3. Modifying the XML data. An attentive user might wish to
replace the age value of a particular pet with a
newer value. Once again, your program could locate the old
value and swap in the new.
Microsoft Internet Explorer 5, currently in beta 2 release,
is the only available application which currently
supports XML via the Document Object Model. Microsoft's XML
support can roughly be bisected: that which conforms
to the W3C's DOM Level 1 Standard and that which is a
proprietary Microsoft "twist". We will focus only
on DOM Level 1 compatible support. We will also only focus
on inspecting the data in the XML tree, which allows
you to query or process. We will not cover modifications
to the data inside the tree, as this is a more advanced
topic best suited to a follow up article.
A Tree Grows in XML
XML via the Document Object Model: A Preliminary Course
XML Objectified: IDOMDocument
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