Mark Baker

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XML is rapidly becoming the way applications communicate. Because it isn't one language but a means to create many languages, it can play many roles in application integration and data exchange. In this article I'll explore some of the varied roles that XML can play by developing a simple middleware application that serves up data from a database. The application (see Listing 1) uses XML in three ways: Requests from clients are encoded in XML. Data sent back to a client is encoded in XML. The database itself contains data marked up in XML. The application is written in OmniMark - a 12-year-old language with a long history in the SGML community - which became a free language in May 1999. It's based on the streaming programming model pioneered by OmniMark and subsequently adopted by SGML and XML translation languages like DSSSL and XSL. Streaming is also the principle ... (more)

Designing XML Tagging Languages

The raison d'être for XML is to make it easy to process structured data. Yet it seems that ease of processing is often the first casualty of XML language design. I mean this in two ways. First, markup language design is often conducted without regard to the ease of processing of the resulting markup language. Second, language designers often forget that XML encodings are easy to process and change into other forms, and thus approach XML languages more as fixed representations of data than as vehicles to transport data between processes. The result is languages that are designed t... (more)

Converting Non-XML Data to XML

Most of the attention in the XML processing area is focused on the decoding of XML encoded data - in other words, XML parsing. One of the key design goals of XML was to make it easy to parse (more specifically, easier to parse than SGML). XML encoding - taking data in a non-XML format and translating it into XML - is a much harder problem. It's easy enough to wrap XML tags around database fields or the properties of objects. But what if you have to take data in other formats - RTF, EDI, any of the thousands of proprietary formats XML is supposed to replace, or even plain ASCII t... (more)

Hierarchy-Based Parsing

OmniMark is the granddaddy of XML programming languages, having begun life as XTRAN, an SGML translation language, in 1989. Designed specifi- cally for filtering structured data, Omni- Mark has a streaming programming model, a rule-based program structure, and integrated XML and SGML parsers. XML programmers are familiar with the tree-based parsing of the DOM and the event-based parsing of SAX. OmniMark uses a third model: hierarchy-based parsing. Where a SAX parser will treat the beginning of an element as one event and the end as a separate event, OmniMark treats the occurrence ... (more)