XML Schema

Hypertext Markup Language (HTML) was widely used to determine how information was displayed on Web pages in the early 2000s. HTML is very similar to Standard Generalized Markup Language (SGML) and a subset of SGML called eXtensible Markup Language (XML). While HTML determines how information is displayed on a Web page, XML deals with the actual information that gets displayed. Its importance to the world of e-commerce centers on its ability to enable information to be shared in a universal way, regardless of the computer systems or applications a company might be using. As ABA Banking Journal explained, "XML is a set of simple rules for converting the meaning of a document written in any software into a globally standardized format that any other software can understand." Alternative ways of sharing information often require companies to make special arrangements.

As with HTML, XML involves presenting data within tags. Models called XML schemas are used to determine how these tags are arranged within a document and to ensure the information they contain is valid based on predetermined criteria. They are more effective and expansive than document type definition (DTD) schemas used by SGML, especially for ensuring the validity of a document. Validity is very important to companies engaging in e-commerce because they populate databases with large amounts of information about potential and actual customers. If bad data is entered into databases, the effectiveness and accuracy of these tools are undermined.

In order to understand how an XML schema works, one could use the example of a customer's contact information. A schema for a customer's addresses could require that certain informational elements (such as name, street address, city, state, and ZIP code) be present in order to be valid. Furthermore, the schema might specify exactly what constitutes valid information within these categories, indicating that ZIP codes contain only numbers, and no more than five of them.

In May 2001, the World Wide Web Consortium (W3C) issued its XML schema specification, which standardized XML schemas. The organization's specification consisted of three parts. The first pertained to how XML software manages numbers, dates, and other forms of information. The second proposed "methods for describing the structure and constraining the contents of XML documents, and defines the rules governing schema-validation of documents." Finally, the third part of the specification was a primer explaining "what schemas are, how they differ from DTDs, and how someone builds a schema."