rfc3072.txt

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12. IANA Considerations

   The compression and encryption algorithms for SDXF is not fixed, SDXF
   is open for various algorithms.  Therefore an agreement is necessary
   to interprete the compression and encryption algorithm method
   numbers.  (Encryption methods are not a semantic part of SDXF, but
   may be used for a connection protocol to negotiate the encryption
   method to use.)

   Following two items are registered by IANA:

12.1 COMPRESSION METHODS FOR SDXF

   The compressed SDXF chunk starts with a "compression header".  This
   header contains the compression method as an unsigned 1-Byte integer
   (1-255).  These numbers are assigned by IANA and listed here:









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   compression
    method     Description                     Hints
   ---------   ------------------------------- -------------
         01    RUN-LENGTH algorithm            see chap. 5
         02    DEFLATE (ZIP)                   see [DEFLATE]
     03-239    IANA to assign
    240-255    private or application specific

12.2 ENCRYPTION METHODS FOR SDXF

   An unique encryption method is fixed or negotiated by handshaking.
   For the latter one a number for each encryption method is necessary.
   These numbers are unsigned 1-Byte integers (1-255).  These numbers
   are assigned by IANA and listed here:

   encryption
     method    Description
    ---------  ------------------------------
     01-239    IANA to assign
    240-255    private or application specific

12.3 Hints for assigning a number:

   Developers which want to register a compression or encrypt method for
   SDXF should contact IANA for a method number.  The ASSIGNED NUMBERS
   document should be referred to for a current list of METHOD numbers
   and their corresponding protocols, see [IANA].  The new method SHOULD
   be a standard published as a RFC or by a established standardization
   organization (as OSI).

13. Discussion

   There are already some standards for Internet data exchanging, IETF
   prefers ASN.1 and XML therefore.  So the reasons for establish a new
   data format should be discussed.

13.1 SDXF vs. ASN.1

   The demand of ASN.1 (see [ASN.1]) is to serve program language
   independent means to define data structures.  The real data format
   which is used to send the data is not defined by ASN.1 but usually
   BER or PER (or some derivates of them like CER and DER) are used in
   this context, see [BER] and [PER].








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   The idea behind ASN.1 is: On every platform on which a given
   application is to develop descriptions of the used data structures
   are available in ASN.1 notation.  Out off these notations the real
   language dependent definitions are generated with the help of an
   ASN.1-compiler.

   This compiler generates also transform functions for these data
   structures for to pack and unpack to and from the BER (or other)
   format.

   A direct comparison between ASN.1 and SDXF is somehow inappropriate:
   The data format of SDXF is related rather to BER (and relatives).
   The use of ASN.1 to define data structures is no contradiction to
   SDXF, but: SDXF does not require a complete data structure to build
   the message to send, nor a complete data structure will be generated
   out off the received message.

   The main difference lies in the concept of building and
   interpretation of the message, I want to name it the "static" and
   "dynamic" concept:

   o  ASN.1 uses a "static" approach: The whole data structure must
      exists before the message can be created.

   o  SDXF constructs and interpretes the message in a "dynamic" way,
      the message will be packed and unpacked step by step by SDXF
      functions.

   The use of static structures may be appropriate for a series of
   applications, but for complex tasks it is often impossible to define
   the message as a whole.  As an example try to define an ASN.1
   description for a complex structured text document which is presented
   in XML:  There are sections and paragraphs and text elements which
   may recursively consist of sections with specific text attributes.

13.2 SDXF vs. XML

   On the one hand SDXF and XML are similar as they can handle any
   recursive complex data stream.  The main difference is the kind of
   data which are to be maintained:

   o  XML works with pure text data (though it should be noted that the
      character representation is not standardized by XML).  And: a XML
      document with all his tags is readable by human.  Binary data as
      graphic is not included directly but may be referenced by an
      external link as in HTML.





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      In XML there is no strong separation between informational and
      control data, escape characters (like "<" and "&") and the
      <![CDATA[...]]> construction are used to distinguish between these
      two types of data.

   o  SDXF maintains machine-readable data, it is not designed to be
      readable by human nor to edit SDXF data with a text editor (even
      more if compression and encryption is used).  With the help of the
      SDXF functions you have a quick and easy access to every data
      element.  The standard parser for a SDXF data structure follows
      always a simple template, the "while - switch -case ID -
      enter/extract" pattern as outlined in chap. 3.4.2.

   Because of the complete different philosophy behind XML and SDXF (and
   even ASN.1) a direct comparison may not be very senseful, as XML has
   its own right to exist next to ASN.1 (and even SDXF).

   Nevertheless there is a chance to convert a XML data stream into a
   SDXF structure:  As a first strike, every XML tag becomes a SDXF
   chunk ID.  An elementary sequence <tag>pure text</tag> can be
   transformed into an elementary (non-structured) chunk with data type
   "character".  Tags with attributes and sequences with nested tags are
   transformed into structured chunks.  Because XML allows a tag
   sequence everywhere in a text stream, an artificially "elementary
   text" tag must be introduced:
   If <t> is the tag for text elements, the sequence:

   <t>this is a text <attr value='bold'>with</attr> attributes</t>

   is to be "in thought" replaced by:

   <t><et>this is a text </et><attr value='bold'><et>with</et></attr>
   <et> attributes</et></t>

   (With "et" as the "elementary text" tag)
















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   This results in following SDXF structure:

   ID_t
   |
   +-- ID_et = " this is a text "
   |
   +-- ID_attr
   |   |
   |   +-- ID_value = "bold"
   |   |
   |   +-- ID_et = "with"
   |
   +-- ID_et = " attributes"

   ID_t and ID_et may be represented by the same chunk ID, only
   distinguished by the data type ("structured" for <t> and "character"
   for <et>)

   Binary data as pictures can be directly imbedded into a SDXF
   structure instead referencing them as an external link like in HTML.

14. Author's Address

   Max Wildgrube
   Schlossstrasse 120
   60486 Frankfurt
   Germany

   EMail: [e-mail]

15. Acknowledgements

   I would like to thank Michael J. Slifcak ([e-mail]) for the
   supporting discussions.

16. References

   [ASN.1]   Information processing systems - Open Systems
             Interconnection, "Specification of Abstract Syntax Notation
             One (ASN.1)", International Organization for
             Standardization, International Standard 8824, December
             1987.

   [BER]     Information Processing Systems - Open Systems
             Interconnection - "Specification of Basic Encoding Rules
             for Abstract Notation One (ASN.1)", International
             Organization for Standardization, International Standard
             8825-1, December 1987.



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   [DEFLATE] Deutsch, P., "DEFLATE Compressed Data Format Specification
             version 1.3", RFC 1951, May 1996.

   [IANA]    Internet Assigned Numbers Authority,
             http://www.iana.org/numbers.htm

   [PER]     Information Processing Systems  - Open Systems
             Interconnection -"Specification of Packed Encoding Rules
             for Abstract Syntax Notation One (ASN.1)", International
             Organization for Standardization, International Standard
             8825-2.

   [UCS]     ISO/IEC 10646-1:1993. International Standard -- Information
             technology -- Universal Multiple-Octet Coded Character Set
             (UCS)

   [UTF8]    Yergeau, F., "UTF-8, a transformation format of ISO 10646",
             RFC 2279, January 1998.

































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17.  Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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