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Combining the power of Xquery & XSLT: toward fulfilling the promise of XML.

Article Excerpt
People communicate with each other online. People buy goods and services from online stores. People pay bills, file insurance claims, and book travel and flights online. Each of these online activities generates digital information such as e-mail, invoices, statements, hotel reservation confirmations, purchase orders, news reports, and technical documents.

One characteristic of this kind of digital information is that it is semistructured data. E-mail is semistructured; it has structured parts, such as from, to, cc, and subject, and an unstructured part, the e-mail body, which can be any text. Reservation confirmations are semistructured too; they may contain structured information, like room rent and hotel address, and unstructured information, such as the hotel description and cancellation policy.

Another characteristic of this kind of digital information is that it's meant both for people to read and for computers to process automatically. XML (see www.w3.orgITR/2000/RECxml-20001006) was invented to represent this kind of digital information, ranging from highly structured data like relational tables to semistructured contents like technical documents and news reports.

XML

XML allows people to create their own vocabulary to represent information through simple tagged texts, called XML documents. The advantages of using XML are:

* XML is simple: An XML document is human-readable text. It contains tags, which help computers to process the text automatically. The tagged text looks like this: New York . An XML document is valid as long as it is well formed (in other words, its begin tag matches its end tag).

* XML is flexible: An XML vocabulary can be easily expanded to add new information. In XML jargon, an XML vocabulary can be defined with a DTD (Document Type Definition) or XML Schema.

* XML is self-describing: The tagged text tells what the text means. For example, New York says that "New York" is the city while New York says that "NewYork" is the state. The XML tags provide context so that a search on XML documents becomes more precise.

* XML contains content only, no style or formatting information: An XML document is different from, for example, Word documents. A Word document contains both content itself and style/formatting information. A correct version of software is needed to read the formatted document. In contrast, since it contains content only, without any style or formatting information, an XML document can always be read without the assistance of software.

These advantages make XML a very popular technology to represent and exchange information. People are creating vocabularies for most vertical industries, creating new XML documents, and converting existing digital contents into XML. I call it information XMLization. In this article XML content and XML data are used interchangeably.

Xquery

To use the massive information in XML intelligently for real business benefits, a powerful query language is required to express sophisticated queries across different kinds of XML data. XQuery (an XML query language) is designed for querying XML data just as SQL is designed for querying relational data. XQuery allows you to navigate the complicated structures in XML, expressing query constraints and constructing the query results. It allows you to query the information stored in XML or view it as XML via integration middleware.

XQuery is still a work in progress. The W3C working draft (see www.w3.org/TR/xquery) is not yet an official W3C recommendation.

XSLT

There will be a multitude of XML documents in different vocabularies. Each organization or vertical industry is defining an XML vocabulary for its own use. EbXML and newsXML are two examples of this kind of XML vocabulary. To exchange XML data such as invoices or orders, the data needs to be transformed from one vocabulary to another. Another benefit of using XML is that it separates data from presentation, so the same data can be repurposed to different devices, such as a Web browser, PDA, and printer. With different...

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