The +exi Media Type Suffix
draft-shelby-exi-registration-01

Abstract

Efficient XML Interchange (EXI) is an XML representation technique specified by the W3C to provie a binary alternative to the standard text XML representation. This document defines a new Structure Syntax Suffix "+exi" for use in a specific class of protocols, where "exi" content-type encoding or the generic "application/exi" Media Type are not applicable.

Status of this Memo

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This Internet-Draft will expire on September 28, 2012.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. When to Use the +exi Suffix
• 3. Security Considerations
• 4. IANA Considerations
• 5. Acknowledgments
• 6. Changelog
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Author's Address

1. Introduction

Efficient XML Interchange (EXI) [W3C.REC-exi-20110310] is an XML representation technique specified by the W3C to provie a binary alternative to the standard text XML representation. EXI is not a generic compression technique like gzip or deflate, but an encoding technique specifically for XML that uses either learnt or pre-informed schema information.

This document defines a new Structure Syntax Suffix "+exi" for use in a specific class of protocols, where the "exi" content-type encoding or generic "application/exi" Media Type defined in [W3C.REC-exi-20110310] are not applicable.

2. When to Use the +exi Suffix

The EXI standard already defines both an "exi" content-type encoding and an "application/exi" Media Type. This sections discusses when it is appropriate to use the new "+exi" Structured Syntax Suffix when registring a Media Type.

Appendix F.1 of [W3C.REC-exi-20110310] clearly describes when the exi content-type encoding should be used: "Protocols that can identify and negotiate the content coding of XML information independent of its media type, SHOULD use the content coding "exi" (case-insensitive) to convey the acceptance or actual use of EXI encoding for XML information."

Thus when a protocol depends on the media type to identify that the payload is EXI, it can make use of the "application/exi" Media Type defined in Appendix F.2 of [W3C.REC-exi-20110310]. This works particularly well for applications using EXI in a generic way, and in particular in non Schema-informed mode, where protocol specific information is not needed to process the payload, in particular the XML schema used. In these cases it is recommended to use the "application/exi" Media Type or "exi" content-type encoding.

The "+exi" Structure Syntax Suffix defined in this document is appropriate for use with a special class of protocols that:

• Make use of a Media Type to identify the semantics of the protocol payload, and offer more that one serialization of the payloads. For example, some protocols may offer JSON, XML and EXI representations, and
• use EXI as a native encoding (without the use of XML as an interemediate) in Schema-informed mode, and the base Media Type together with the SchemaID indicates to the protocol the Schema that was used to produce the EXI grammar as described in Section 4.

3. Security Considerations

Security considerations are discussed in Section 4.

4. IANA Considerations

This document requests registration of the Structured Syntax Suffix "+exi" as follows, following the registration template from Section 6.2 of [I-D.ietf-appsawg-media-type-regs].

Name:

Efficient XML Interchange

+suffix:

"+exi"

References:

The EXI standard is defined in [W3C.REC-exi-20110310], in particular Schema-informed Grammars are defined in Section 8.5 and the "applicatio/exi" Media Type is defined in Appendix F.2.

Encoding considerations:

Binary

Interoperability considerations:

The registration of a Media Type using this suffix MUST describe how to determine the XML Schema that is used to encode/decode a payload identified by that Media Type. In particular this description defines how to determine the Schema used to encode a payload using the SchemaID option of the EXI header. The format of the identifier to be used in the SchemaID, a reference to where the corresponding Schema is defined, and a description of how future versions of such Schemas will be handled MUST be included. A default Schema version in the absence of the SchemaID field MAY be defined.

Security considerations:

The "+exi" suffix shares the same security considerations as XML, described in [RFC3023], Section 10. In addition, the security considerations discussed in the Media Type registration for "application/exi" apply as defined in Appendix F.2 of [W3C.REC-exi-20110310].

Contact:

Apps Area Working Group (apps-discuss@ietf.org)

Author/Change controller:

The Apps Area Working Group has change control over this registration.

5. Acknowledgments

This draft is the result of discussions on the Apps Area Working Group mailing list. Thanks to Carine Bournez and Guido Moritz for their helpful comments.

6. Changelog

7. References

7.1. Normative References

7.2. Informative References

Author's Address