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Workshop on Standardization in E-Health
Geneva, 23-25 May 2003


ASN.1 and its use for e-health standards

This presentation provides a brief history of ASN.1 and some of its uses today. It then examines alternative notations and techniques for defining the form and encoding of electronic messages, from the earliest days of bits and bytes to the current use of XML. There is particular emphasis on ASN.1 and the role it has played over the years and the facilities it offers to day to those producing standards for electronic communication. ASN.1 can be used as an XML schema notation, where it provides the same functionality as use of XSD (W3C XML Schema), but it also makes compact binary representations of the data available as well as XML encodings. It is the notation of choice for many ITU-T Recommendations.

There are a number of technical advantages of ASN.1 over other notations that might be used in defining e-health standards. It 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. This enables to tools to easily and simply map ASN.1 into C, C++ or Java data structures, with encode/decode libraries available for any computer platform. The encode/decode libraries typically support several binary formats as well as XML formats, and includes provision for both "extensibility" and canonical encodings in all formats.

Several examples are given of ASN.1 specification, including examples of XML encodings, and some comparisons with XSD, the W3C Recommendation for the notation for defining XML formats.

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