XML standards battle is brewing over Navy's data-sharing plans

'Rules ensure that every XML instance of a document will be consistent. Contractors will know exactly what is required and will not be presented with competing requirements.'

'Robert Green

Laurie DeWitt

Proposed Navy rules for Extensible Markup Language use are forcing other agencies to take a stand on how they share and reuse data.

The Navy plans to adopt international interoperability standards that would eliminate document type definitions, or DTDs, which many agencies now use for sharing documents. Newer XML schemas are more suited to individual data elements.

The CIO Council took the Navy's 2001 XML developer's guide as the basis for its own 2002 governmentwide guide, at xml.gov. Now the Navy is further standardizing use of XML elements, attributes, types and schemas across all service programs, said Robert Green, XML interoperability team leader in the Navy CIO's office.

XML is part of several initiatives to make the Navy network-centric. 'We are looking at XML from a strategic and tactical perspective, not just as a convenient mechanism for describing markup' of documents, Green said.

The original guide 'was the Navy's first attempt at standardizing XML development,' Green said, and it left some questions unanswered. For example, it did not say whether program managers should follow the World Wide Web Consortium's XML Schemas standard for shared vocabularies across platforms.

The new rulebook endorses the W3C XML component recommendations, as well as others from the International Standards Organization, the Organization for the Advancement of Structured Information Standards, the OASIS Universal Business Language technical committee, and the United Nations Centre for Trade Facilitation and Electronic Business.

By adhering to worldwide standards, the Navy intends to base its future applications more heavily on commercial products, Green said, in accordance with Office of Management and Budget Circular A-119, which encourages voluntary consensus standards.

XML salad

A set of XML naming rules will let different Navy programs share their XML components, Green said. 'Rules ensure that every XML instance of a document will be consistent,' he said. 'Contractors will know exactly what is required and will not be presented with competing requirements for different entities.'

The new guide warns program managers to steer clear of proprietary XML extensions. 'Many vendors add customizations to specifications, in an attempt to build market share,' but customization leads to proprietary implementations and costly middleware, Green said.

Two years ago the Government Accountability Office, then the General Accounting Office, also warned agencies against proprietary XML extensions in its report, Electronic Government: Challenges to Effective Adoption of the Extensible Markup Language.

The fact that the core XML standard is nonproprietary does not ensure that all applications built with it will interoperate. 'It is easy [for a vendor application] to add elements to an XML document that place unique processing requirements and restrictions on the document, preventing other systems from being able to interpret it,' GAO said.

The Navy's plans to adhere strictly to worldwide standards has sparked argument among federal XML users. The draft rulebook mandates use of the XML Schemas definition, or XSD, instead of the older document type definitions. Both DTDs and schemas can set valid data types for applications. The decision set off a debate among members of the CIO Council's XML Working Group.

John Weiland, an IT specialist for the Naval Medical Information Management Center, posted a mailing list request for feedback on the draft. The Navy has formed a Business Standards Council, he said, to coordinate XML constructs from different functional areas, such as logistics.

But the Navy's intent to ban DTDs seemed 'overly restrictive' to Ken Sall, an e-government expert for consultancy SiloSmashers Inc. of Vienna, Va. 'I agree that XML Schemas is much more powerful than DTDs for data-oriented models,' he wrote to the mail list, 'but there are still times where what we model in any agency is more document-oriented.'

Other working group members said DTDs work better in some legacy implementations and produce much smaller files.

Winchel 'Todd' Vincent III, who heads Atlanta consultancy WTVIII Inc., noted that a typical DTD court document is 14K in size, whereas a court filing with much the same information using schema, developed under California's Second Generation Electronic Filing Specification, runs larger than 250K. Generally speaking, the larger the DTD, the more work an application's XML parser must do to format a particular document or message, he said.

David Heiser, an XML expert at the IRS, also weighed in, noting that the tax agency uses both DTDs and schemas in its architecture. One reason it stuck with DTDs was to eliminate the cost of incorporating schemas into legacy Standard Generalized Markup Language applications. Another reason: XML's immaturity.

'XML schema is not advanced enough,' Heiser wrote, 'and tools and standards need further development (publishing tools in particular) before I could recommend the outright ban on XML DTDs.'

Because IRS 'will be publishing to [Adobe Portable Document Format on paper] for decades to come,' he wrote, the visual presentation requires tools and techniques 'that I don't feel are quite yet supported by XML Schemas.'

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