In Delivering XML, SGML and HTML From Databases, John Chelsom, CSW Informatics Ltd, set out to show how database information could be delivered via the web. After providing an overview of Web architectures, Chelsom discussed how CGI scripts can be used to query databases and return results in HTML documents. If this is possible, why not query SGML documents, or SGML objects stored in databases. Chelsom referred to a blurring of the document/database boundary. Ideally, it would be more interesting to query a database and return SGML to the client, refining the search at the client side.
Such a scenario needs an SGML parser as a front end and Chelsom suspects that writing an SGML parser in Java would be a daunting, if not impossible, task. A second possibility is not to use SGML, but simply to provide direct communication with the database via a Java applet. This would require a fixed set of forms. Such a scenario, however, quelches the spirit of discovery, as the Java applets only work well if you know where to look and the structure you re looking for. Enter XML. Chelsom noted that XML has the structure to act as a database, and it is possible to write an XML parser in Java. Instead of a form-based approach on client side, we can use a query mechanism primed with DTDs, which represents the database schema. Such queries can run on the server or on the client side.
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