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IBM developerWorks: Dare to script tree-based XML with Perl

Jul 09, 2000, 15:47 (0 Talkback[s])
(Other stories by Parand Tony Darugar)

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"Parsing an XML document into tree structures makes it possible to operate on the tree structure of the data. Find out how to use the functions for accessing and manipulating the document tree, and follow a sample stock-trading application that uses Perl, DOM, XML, and a database to evaluate trading rules. (You can apply the same techniques with other scripting languages, including Tcl and Python.) This is the second installment on using scripting languages to manipulate and transform XML documents."

"My previous article discussed how to manipulate XML with scripting languages, and Perl in particular. In the course of parsing a file that way, handlers are called as each tag is encountered. That provides a very efficient means of processing XML, both in memory usage and processing time. However, certain tasks are difficult to accomplish in the event-based methodology. Imagine, for example, needing to move or rearrange certain segments of the document or sorting items within the document. Because the document is processed as a stream, we would first need to store the components before sorting or rearranging them. A mechanism that would store the components automatically would make such tasks substantially easier."

"XML documents are required to be well-balanced, making it easy to store them as trees. Once you parse XML documents into tree structures, you can then operate on the tree. This yields a great deal of flexibility in dealing with the documents: you can access the components of the document in random order, rearrange them, and add or remove them. This is especially appropriate for applications in which the flow of processing is based on external logic, as opposed to the order and occurance of elements within the XML document. Storing the document as a tree enables random access to its data and structure, instead of having the processing governed by when and where the tags and elements occur."

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