How XML enables dynamic content
Almost every Web site offers some form of dynamic content. Whether it's stock quotes, personalized account information or movie show times, users expect customized information to be delivered quickly and accurately.
As more firms build dynamic Web sites, they are turning to XML-based Web content management and delivery systems to help manage, integrate and communicate information to constituents in real time.
The key to the systems is their XML base. XML enables the separation of content from business logic and presentation. By defining the content of a document separately from its formatting, XML makes it easier to reuse the content in other applications or presentation environments.
To understand XML's role in dynamic Web content delivery, one must first understand the concept of tags. Like HTML, XML uses elements and attributes, which are indicated in a document using tags. But unlike HTML - which only can describe how to display content, not what the content is - XML enables tagging of information in a document that describes what that content is about, in explicit terminology and implicit nesting structure.
XML's tag structure lets users define and index sets of data however they wish - that is, to structure documents according to their needs. An XML-tagged document could contain the following:
<title>XML for Fun & Profit</title>
<title>This is section one.</title>
<acme:p>This is the first paragraph.</acme:p>
The benefits of XML's self-describing capabilities are enormous, including making it easy to manipulate content - search it, repurpose it and display it differently. Because information is identified contextually, queries retrieve only relevant files, making online searches more efficient. And because each piece of content is tagged, XML-based Web content management and delivery systems have the ability to pick out particular components from the database and repackage the information to construct multiple pages.
Business logic, the set of rules for what the data should do, can be applied to data as it is served to an individual visitor to govern the right presentation of data for that audience. For example, if a supplier visits a Web site, he should see content that is geared specifically for him, whether it's pricing or account information. This pricing and account information, of course, will be customized for different visitors - employees, retailers and direct buyers will see completely different content than a supplier or customer.
Because HTML has been the language used by most Web publishers in the past, a strategy for migrating to XML is necessary. Some content management/delivery systems enable gradual migration to XML by providing templates that handle both XML and HTML. These systems leverage XML to remove the formatting instructions of HTML files and dynamically reformat them with a new design from a template. This enables companies to change the look and feel of their sites easily. They can develop "private label" templates that use the logo, look and feel of a given reseller, supplier or distributor, but pull content from a central data repository. By doing that, even though the data source is the same across all, the look and feel of the data meets the unique requirements of each partner's site.
The other migration issue with XML is that most browsers still see only HTML. Therefore, finding a content management system that has the ability to transform XML to HTML on the server level, before it is sent to the user's browser, is critical. Some systems do this by "walking" the tree of an XML document, scanning each tag and building an HTML file by combining the tags and a template, which incorporates the business logic that has been scripted. The result is a dynamic document that changes in response to changes in content, logic and/or presentation.
Though only at the beginning of its adoption curve, XML is proving it can improve the way Web content is created, managed and published.
Vogel is chief technology officer for eBusiness Technologies in Providence, R.I. He can be reached at firstname.lastname@example.org.
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