Fabrice Desré France Telecom R&D DTL/TAL

France Telecom was the initiator of the ITU-T Rec X.694 | ISO/IEC 8825-5 "Mapping W3C XML Schema Definitions into ASN.1" standard. This standard specifies how to translate a W3C XML Schema into an ASN.1 module to take advantage of the compact PER coding associated with ASN.1. Using X.694, XML applications can benefit natively of ASN.1 strength : reduced bandwith usage (both for bandwith limited networks and to reduce latency on broadband networks) and parsing time, small decoders with easy to use APIs. To promote this standard, we developed the first prototype implementation of X.694, which is freely usable from our web site.

We are interested in a broad range of applications, from gigabytes transfers between applications as seen in datacenters, to efficient data transmission for mobile networks. This also includes satellite transmissions, e-commerce and m-commerce applications, object identification and web services. We especially expect X.694 to be used to encode web services payloads. For instance, the OASIS UBL schemas library, while being normalized as a W3C XML Schema, is also available as a collection of ASN.1 modules, thanks to the automatic mapping. Combined with the upcoming X.695 (aka "Fast Web Services") work, X.694 provides a full solution for efficient use of XML and web services in constrained environments.

ASN.1 being a non proprietary and patent unencumbered technology, there are already lots of ASN.1 tools, both from commercial vendors or freely available that supports the PER encoding. This is a CPU efficient encoding, and its canonical variant allows digital signature and encryption. The low CPU requirements makes it possible to exchange XML documents with devices that are deemed to have little processing power and limited bandwith. On the other hand, gzip is known to need higher CPU and memory usage, and to be slower, due to its on-the-fly building of the dictionary. Another advantage of the use of ASN.1 tools that they don't share with their XML counterparts is the overhead of processing. They allow fast and direct marshalling and unmarshalling of the data to programmatic types, in many different languages including C, C++ and Java. This data binding is a considerable improvement for the toolkit users. ASN.1 tools also benefit from 20 years of evolution of the supporting standard. These tools are thus highly optimized, well documented and debugged.

X.694 is specifically designed to provide an efficient mapping from the W3C XML schemas, so it does not support as-is other schema languages. However, using tools like Trang it's easy to translate DTDs and RelaxNG schemas and use the resulting W3C schemas with X.694.