XML and Java: Why These Two

New Java software targeted for use with XML appears every month. What is it about XML and Java that make them such a good match? On the surface it may be hard to see the fit, since the two seem to be very different. After all, XML is a markup language, while Java is a programming language. XML is a standard promoted by the World Wide Web Consortium (a large group of nearly 300 companies, universities, and government agencies with diverse interests), whereas Java is essentially a de facto standard controlled by a single software and hardware company, Sun Microsystems.

Many web developers have come to the conclusion that XML and Java are the perfect pair because they complement each other so well. XML contributes platform-independent data -- portable documents and data. Java contributes platform-independent processing -- portable object oriented software solutions. In the primordial XML days of March 1997, Sun Microsystem's Jon Bosak [1] wrote in his seminal article, XML, Java, and the Future of the Web, that: "XML gives Java something to do". That is, XML provides the data for Java to process in several specialized application areas:

"The applications that will drive the acceptance of XML are those that cannot be accomplished within the limitations of HTML. These applications can be divided into four broad categories:

1. Applications that require the Web client to mediate between two or more heterogeneous databases.
2. Applications that attempt to distribute a significant proportion of the processing load from the Web server to the Web client.
3. Applications that require the Web client to present different views of the same data to different users.
4. Applications in which intelligent Web agents attempt to tailor information discovery to the needs of individual users."

The applications that Bosak referred to over a year and a half ago are finally beginning to appear, thanks to the combination of XML and Java. Bosak recently wrote an article for IEEE Computer entitled "Media-Independent Publishing: Four Myths about XML". In that October 1998 article, Bosak gave us another quotable gem: "XML can do for data what Java has done for programs, which is to make the data both platform-independent and vendor-independent."

Both XML and Java are Internet friendly. XML was designed to be an optimized, flexible, readable format which is straightforward to use over the Internet; Java has been network-aware from the beginning in its support of sockets, HTTP, HTML, and servers. Both support Unicode (two byte characters) and therefore contribute to internationalized applications [2]. Much as Java provides programmers the ability to represent complicated data structures and object-oriented models (sometimes in a tree or table view), XML is ideal for representing complex, hierarchical data models. While Java developers have benefited from a rich development environment for several years, XML proponents are more recently experiencing the widespread availability of tools to support their ability to write applications that process XML documents. (Some may argue that truly mature XML authoring tools have not yet arrived. No argument here.)

Although there are many XML tools and libraries based on other languages such as Python, perl, and C, the majority of XML development is focused on Java, which is emerging as the language of choice for processing XML. In mid September 1998, JavaSoft posted its first Early Access release of the XML Library (discussed in detail in Part 2 of this article), indicating Sun's interest in providing a standard interface to XML from Java. It is unclear whether this will eventually become one of the Core packages of the Java Development Kit (JDK), but this seems like a highly desirable scenario. Why? Well, if JavaSoft includes the XML Library in a future JDK, then any browser that supports the corresponding Java Virtual Machine (JVM) will by definition contain full and identical support for XML processing. Developers would not have to download generic XML code with their applets or applications. On the other hand, Sun may choose not to include the XML Library in JDK to keep the size of JDK smaller (but not by much). [3]

Part 1 concludes with a discussion of terminology which is fundamental to the discussion of using XML with Java. Parts 2 and 3 of this article will present a survey of all significant Java/XML efforts. Readers who know of others are encouraged to submit them to the author for consideration in subsequent updates. Those interested in XML software in languages in addition to Java are directed to our earlier article, the XML Software Guide, which, like this article, is also updated periodically.

[1] Bosak, considered by some to be the inventor of XML (along with Textuality's Tim Bray and Microsoft's Jean Paoli) became the chairperson of an SGML effort that evolved into the XML Working Group of the W3C.

[2] Internationalization is often abbreviated as "i18n", with the 18 signifying the number of letters between the "i" and the "n", as many X Window System developers may recall.

[3] If you're interested in encouraging Sun to add the XML Library, please consider joining the Web Standards Project.

XML and Java: The Perfect Pair: Part 1
XML and Java: The Perfect Pair: Part 1
XML and Java: Definitions