XML Schema will speed adoption

A key XML standard from the World Wide Web Consortium, XML Schema, is going to make it easier, simpler and cheaper to use Extensible Markup Language in business applications next year.

eWeek Labs sees XML Schema as the most important XML standard to be released since XML itself. It will give applications the ability to check incoming XML documents for correctness—a key prerequisite to the widespread use of XML as a data interchange standard.

The long-awaited XML Schema specification reached the key milestone of W3C candidate recommendation status on Oct. 24. Schema will likely reach final status by the end of this year or early next year. With tool and server support for Schema and other XML-based protocols growing, round-trip XML communications will become much easier.

Schema opens doors

schema is fundamental to xmls continued adoption in the enterprise. With Schema in place, organizations can add business constraints to XML document definitions to ensure that XML documents are formatted correctly. This functionality is critical when a company is receiving XML data from several trading partners or other external sources—data that might be improperly formatted or be missing required information.

Schema doesnt perform the high-level checks that a database can do on incoming data, such as referential integrity checks.

For example, Schema can tell whether the listing of a part number is syntactically correct—having the correct combination of letters and numbers, for example—but not whether that part number is in the current catalog. Software applications that perform this kind of database-driven validation of XML data will be hot items in the next few years.

Schema also dramatically improves XML by providing built-in data types and user-definable, complex XML data types. Because XML is a text format, XML data is transmitted as text characters. Schema provides a way for XML parsers to identify an XML element or attribute as a number, a date, a string or another higher-level data type. Schemas strong typing system allows an XML parser to check a typed element for syntax errors. Schema uses a type system based on the ISOs 11404 (Language-Independent Data types) standard, as well as on SQL database and Java data types.

Going beyond simple types, Schema also lets users build compound or complex data types that reflect higher-level structures in their XML documents. The classic example of a structure is a purchase request. The request contains an order, an amount and the buyers shipping information. Contained within the order are line items, each of which contains a part number, a description, a unit price, a quantity and an extended price.

Schema provides a way to describe these structures so that an XML parser can read through an incoming XML document, identify it as a particular type of purchase order and check each element in the XML hierarchy to make sure all the required subcomponents are present and have valid values.