Why use XML Schema to define taxonomies?
At risk of sounding overly enthusiastic, the use of XML Schema for the core XBRL taxonomy document gives XBRL users considerable power to validate their XBRL instance documents, checking that only defined concepts are reported and checking that facts reported have the correct data type etc. By leveraging XML standards like XML Schema, XBRL buys users a whole lot of validation power built into any XML Schema compliant validator. Note however that XML Schema validation does not guarantee XBRL validation. In the words of David vun Kannon, XBRL validity is a superset of XML Schema validity. There are some things that the XML Schema language does not have the power to enforce, even if the implementations were perfect. For instance, if XBRL’s item and context elements had a simple ID/IDREF relationship, XML Schema could enforce it. Since we use substitution groups and the item element is abstract, XML Schema cannot enforce it. This limitation means that there is room for new tools to provide
