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XML in Action : Page 6

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"We see XML schemas as providing the rules of engagement for the new initiative of Web solutions. Our tools empower Internet programmers to make the move from where they are to where they need to go."

Chapel Hill NC based Extensibility has focused on the task of creating schemas and in June 1999 brought out its XML Authority schema editor. A schema defines the rules of a document or database. DTDs are the current schema of choice for XML documents. In June 1999 we talked with company founder Reid Conrad about schemas and what they mean to web designers and developers.

Q: What exactly is a schema?

XML schemas represent the objects, and their properties and relationships for an XML application. The schema identifies the components and provides the rules by which XML documents are created, validated and processed. Consider XML schemas as the grammar for a customized Internet ready vocabulary.

Q: What's the difference between a DTD and a schema?

Document type definitions (DTD's) were derived from SGML and are a component of the XML 1.0 specification. Early on it was clear that DTD's lacked descriptive capabilities, such as data-typing and inheritance that would enable broader implementation of XML.

Recently, the W3C's Schema Working Group submitted a working draft detailing a new XML schema standard, the XML Schema Definition Language, (XSDL). XSDL promises to bridge schema requirements for both the structured content and data processing worlds. Note, in the meantime there are three other choices for advanced XML schema formats; XML-Data, SOX and DCD. Microsoft's current validating XML parser supports XML-Data. We find many people turning to XML-Data today as they await the completion of the XSDL specification.

Q: Should a Web designer need to worry about schemas? Or is it something you consider a programmer's task?

I wouldn't say worry, rather embrace. Most serious Web designers will want to define the rules for their XML applications. They are in driver's seat.

XML schemas provide Web designers a framework to build sophisticated web based applications. Often, these applications will tap existing information systems. We see diverse groups collaborating on schema design and management. Web designers, database programmers and structured document people are coming together with XML. XML schemas enable them to codify a common set of rules to work together.

Q: Some people equate a structured approach with losing creativity. They say having a schema locks you into a way of thinking and prevents you from coming up with new ways to approach information. Is there any truth to this? Can you clarify the relationship between being creative and using a structured approach?

Remember, XML is extensible. Extensibility enables creativity. XML schemas simply enable the creator to codify creativity. Consider that schemas themselves may reflect varying levels of flexibility and you realize that XML schemas represent a framwork for creativity.

On this point, users should also consider creative development techniques. We believe that XML solutions will best be created in an iterative fashion. This is especially the case for ecommerce solutions. As business rules evolve, so should the schemas.

Q: A well-formed XML document doesn't need a DTD. Do you think it is a good idea include one as a rule of thumb anyway?

Great question. No doubt many XML documents will be processed as well-formed documents. Occassionally, you read "well-formed or valid XML". We see the need for both. The answer becomes evident when you consider the design, testing and production phases of XML development lifecycles.

The design of an XML schema represents a great starting place in the lifecycle of an XML application. With the components and the rules of an XML application identified, the development lifecycle is accelerated. Moreover, the schema can be shared and reused by others providing the basis for standardization.

As the application is being tested, the schema provides the basis for the test. This gives Web designers a safety net in their XML implementation.

Finally, the need to validate content and process on the Internet is intensifying. We see the trend for more online validation versus less. This is especially the case as ecommerce applications proliferate the Internet. Corporations will want to exchange schemas to facilitate secure transactions.

Q: What made you "buy in" to XML and why did you focus on the schema portion of the process?

Early on, it was clear to us that XML would be huge. It's ability to provide common ground for accessing and processing diverse forms of content is awesome. At once, it provides Web applications the flexibility and structure lacking today.

We see XML schemas as providing the rules of engagement for the new initiative of Web solutions. Our tools empower Internet programmers to make the move from where they are to where they need to go.

Q: There's been some talk about DTDs being replaced. Should Web builder hold back on implementing XML solutions until this issue is resolved? Why/why not?

XML is enabling the next generation of Internet applications to exist. This includes e-commerce solutions and weblications. Serious XML initiatives require schemas. Who can wait? Few businesses are willing to miss what XML brings to ecommerce.

When we built XML Authority we knew there would be uncertainty regarding an advanced schema syntax for some time and wanted to reduce the risk of deployment. That's why XML Authority provides syntax output for all of the potential schema standards including DTD's, XML-Data (IE-5 level), XSDL, DCD's and DDML. Our users are getting an edge without the risk.

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