Why use SML?
According to Bill French, chief architect at StarBase, there are four types of application where XML is an appropriate technology:
1. As a mediator between databases
This is relatively easy to achieve, French says. Such a task is primarily a question of mapping one set of tags onto another. Companies such as Tibco offer tools that facilitate this process.
2. To shift the processing load from the Web server to the client
Since XML delivers not just the data but also an indication of its meaning, it simplifies the task of creating robust client-side software--minor changes in format or structure are less likely to be disruptive.
3. Delivering different views of the same data
French says XML is a key technology in having a Web client deliver different views of the same data to different users. The server can deliver a single XML document (thus reducing the processing load), but the client software customises its presentation according to the needs of a particular user. For example, a cinema's Web site might present a table of screening times for a particular movie. If you wanted a text to speech gateway to relay that information over the phone, the task would be much easier if the data was marked up in XML rather than HTML. Another example is that one XML document can be rendered in different ways on different devices (eg, a computer or a PDA) according to XSL style sheets resident on each device.
But Rob Janson, CTO at e-commerce software developer Hubbub Group and chairman of the Melbourne XML Users Group, warns that the combination of XML and XSLT raises scalability issues. In situations where you can't guarantee that the client can perform the transformation, the server must do it instead and as the load increases, the processing required may be greater than needed for other technologies such as ASP or JSP. On the other hand, XSLT is good when you need to make XML documents you've received human readable.
4. To facilitate information discovery
Finally, XML is appropriate for intelligent Web agents that attempt to tailor information discovery to the needs of individual users or arbitrate commercial transactions, as it simplifies the task of identifying information.
This characteristic of XML also has implications for people searching the Web for information. Is "mercury" a reference to an element, a planet, an early US space program, a deceased rock star, or a character from a 1960s children's TV show?
It's possible that widely used XML tags could help narrow the scope of a Web search. For example, requiring that the data must be located inside a (hypothetical) < lastname > tag would most likely limit the results to references to people's names.
