This paper describes the emergence of ASN.1 as an XML schema notation. Use of ASN.1 as an XML schema notation provides the same functionality as use of W3C XML Schema (XSD), but makes compact binary representations of the data available as well as XML encodings.

ASN.1 also provides a clear separation of the specification of the information content of a document or message from the actual syntax used in its encoding or representation. (Examples of representation differences that do not affect the meaning - semantics - being communicated are the use of an attribute instead of an element in an XML encoding, or of space-separated lists instead of repeated elements.)

Examples are given of ASN.1 specification of an XML document, and some comparisons are made with XSD and RELAX NG