Garbage in, garbage out - it's an axiom that applies to many aspects of enterprise development, but none more so than building reliable and robust Web applications and integration projects with XML. Since its inception, XML has been seen as the cure-all for every problem related to Web application development. However, poorly written XML can either slow down an integration project, or worse, cause the integration project to collapse.

It's important to understand some of the inefficiencies of XML, as well as how you can "clean up" and prevent the use of poorly written XML in development projects. After all, system performance is only as good as the data received and the instructions given. If errors are contained in the XML, it is more likely than not that the system will crash.

One of the main benefits of XML is that it provides mechanisms for verifying document validity through the use of Document Type Definitions (DTDs) and XML Schemas. When creating an XML document, developers can reference either of these mechanisms from within the document itself. The DTD or schema that is referenced will specify exactly how the XML document is to be processed, which elements and attributes are contained in the document, and the order in which these elements and attributes should be listed.

While referencing DTDs or schemas can guarantee the validity of XML documents, there is no requirement that developers use headers to reference DTDs or schemas at all. In fact, developers need only to follow simple syntax rules in order for an XML document to be "well-formed." However, a well-formed document is not necessarily a valid document. Without referencing either a DTD or a schema, there is no way to verify whether or not the XML document is valid. Therefore, measures must be taken to ensure that XML documents do, in fact, reference a DTD or schema.

To guarantee that an XML document references a DTD or schema, development teams can adopt a rule-based system that can detect and prevent errors within the XML code. Developers can create rules that impose constraints on XML documents to verify validity.

XML is created in plain text and utilizes actual words or phrases that have specific meanings to developers. However, even though XML can be read and written by humans, it does not necessarily mean that humans can understand XML - developers can still create unreadable XML code. An element that has a specific meaning to one developer may be of no use, or make no sense, to another developer.

To prevent ambiguous XML code, development teams must mutually agree upon a standard XML vocabulary. With a standard language in place, developers within a team will be more apt to understand each other's code. Naming conventions can be established that verify whether code follows rules that verify anything from W3C guidelines for a specific language, to team-naming standards, to project-specific design requirements, to the proper usage of custom XML tags.

Although the W3C has made an effort to establish a common language, vocabulary, and protocol for XML, these standards are still in development and are constantly changing. Companies that adhere to proposed standards that are not yet fully mature must be prepared to keep up with any changes of those standards in the future. Without any stability in XML standards, developers are forced to either keep up with the rapid changes or fall behind.

In spite of the chaos of standards that may exist for XML development, the recent release of Basic Profile 1.0 provides some guidance to developers seeking a widely used XML standard. The Web Services Interoperability Organization (WS-I) Basic Profile 1.0 consists of specifications that establish a baseline for interoperable Web services. These specifications provide a common framework for implementing XML and building integration projects. Therefore, developers can be confident that the XML standards they use will not be privy to constant flux and change if they create rules that enforce these standards.

If it is written and used properly, XML offers many advantages that can support reliable and robust Web applications. The key to successfully using XML in an integration project is to first understand the inefficiencies that may cause poorly written XML, then utilize the proper techniques that verify correctness at each level of the implementation.