XML stands for Extensible Markup Language. XML acts as the basis for more specialized markup languages such as GML, GeoSciML, and KML.

Because XML elements are functionally similar to database fields, USGIN specifies the usage of XML documents as an interchange format for database records. To use XML documents as an interchange format, USGIN defines XML schemas in which each XML document corresponds with a specific database record and each element in a given XML document corresponds with data entered in a database field. In these documents, elements define the database fields.

For example, a Date field containing the date 12/7/1941 would appear as follows in an XML document:

<date>12/7/1941</date>

For a much more detailed overview of XML, see the USGIN XML Tutorial.