Network Working Group                                   D. Crocker
Internet Draft                              Silicon Graphics, Inc.
Expiration <4/94>                                   5 October 1993
                                
                                
                                
                                
                                
                    MIME Multipart/Header-Set


                 draft-crocker-headerset-00.txt
                                
                                                                



STATUS OF THIS MEMO

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SUMMARY

Data often are aggregated with an initial set of descriptor
information, followed by some number of user data portions.  This
specification formalizes the occurrences of such aggregations as
a MIME Multipart Content-type.  It is intended that MIME
processors which are aware of the Header-Set construct will be
able to process the user data portions, even when they do not
understand the specific header (or descriptor) information which
begins the set.







D. Crocker                                                       1


Internet Draft        Multipart/Header-Set    (Expiration:  4/94)


TABLE OF CONTENTS

1.        INTRODUCTION
2.        Header-Set Content-Subtype Usage in MIME
3.        Header-Set Specification
4.        Header-Set Examples
7.        REFERENCES
8.        SECURITY CONSIDERATIONS
9.        ACKNOWLEDGMENTS
10.       CONTACT



1.  INTRODUCTION

Data often are aggregated with an initial set of descriptor
information, followed by some number of user data portions.  Such
aggregations derive from a specialized environment, such as a
particular operating system file structure, or a tailored
communication environment, such as privacy enhanced mail.  In
particular, one portion of the data contains all of the data
special to that environment and the remainder is regular user-
data, possibly of a type registered within MIME [BORE92].

This specification formalizes the occurrences of such
aggregations as a MIME Multipart Content-type.  It dictates that
the descriptor header information shall occur as the first MIME
body-part at the beginning of the Multipart set, and is then
followed by one or more MIME body-parts containing user data.

It is intended that MIME processors which are aware of the Header-
Set construct will be able to process the user data portions,
even when they do not understand the specific header (or
descriptor) information which begins the set.  As an example, a
recipient on one operating system may still be able to identify
and process the user-data portion(s) even when the specific
header descriptor is intended for an entirely different and
unrelated operating system.  In addition, specifications for MIME
usage which conform to this model will not need to define two
MIME types, one for the Multipart containing "bucket" and one for
the specific Application label to distinguish the portion
containing application-specific data.







D. Crocker                                                       2


Internet Draft        Multipart/Header-Set    (Expiration:  4/94)


2.  Header-Set Content-Subtype Usage in MIME

Header-set information is specified by:

MIME type name:                 MULTIPART

MIME subtype name:              HEADER-SET

Required parameters:            Any pertaining to MULTIPART/Mixed

Optional parameters:            Any pertaining to MULTIPART/Mixed

Encoding considerations:        none

Security considerations:        See separate section in the
                                document.

Published specification:        Contained in the following
                                section.

Rationale:
       
       Permits recipients to process user-data even when they
       cannot process the more specialized header descriptor
       information.  Also, reduces the number of registered MIME
       Content-types, since those which conform to this model
       need to register only an Application sub-type and are not
       also required to register a Multipart subtype.

Contact-info:                   See Contact section, below.

Detail specific to MIME-based usage:
       
       Provides for a MULTIPART MIME body-part which declares
       that the first sub-part in the MULTIPART shall contain a
       header which provides descriptive information about the
       one or more remaining sub-parts in that MULTIPART.  It is
       expected that the first sub-part will typically be an
       Content-type:Application sub-type.



3.  Header-Set Specification

A MIME Content-Type:Multipart/Header-Set body part is a distinct
section of a message and contains two, or more, sub-parts within
in.  The first sub-part is the header and any following sub-parts
compose the set of user data associated with that header.

D. Crocker                                                       3


Internet Draft        Multipart/Header-Set    (Expiration:  4/94)


Typically, the header sub-part will be a registered Content-
Type:Application sub-type, but this is not required.

The Content-Type:Application subtype will declare the "context"
and base of interpretation for processing the MULTIPART body-part
in its entirety.  However, the user data body-parts may also be
processed separately, to the extent that the receiver understands
the individual MIME subparts.



4.  Header-Set Examples

Assume that a user is sending data from the FOO file system, with
its file-system specific information registered as
Application/Filesys-FOO, and the user data containing US-ASCII
text:


To:
Subject:
From:
Date:
Mime-Version: 1.00
Content-Type: MULTIPART/HEADER-SET; boundary=Boundary-1

--Boundary-1
Content-Type:    APPLICATION/Filesys-FOO

(Descriptive information specific to the FOO file system's
storage of the following user data.)

--Boundary-1
Content-Type:    TEXT/plain

(Regular text user-data)

--Boundary-1--


7.  REFERENCES

[BORE92]    Borenstein, N. & Freed, N., "MIME
            (Multipurpose Internet Mail Extensions):  Mechanisms
            for specifying and describing the format of Internet
            Message Bodies.  March, 1992, Network Information
            Center, RFC 1341.


D. Crocker                                                       4


Internet Draft        Multipart/Header-Set    (Expiration:  4/94)


8.  SECURITY CONSIDERATIONS

Specific header parts may contain security-related information.
To the extent that Header-set facilitates the transmission of
operating-system sensitive data, it may open a door for easier
relaxation of security rules than is intended either by the
sender or the administrator of the sender's system.



9.   ACKNOWLEDGMENTS

Header-Set developed from the continuing 882ext working group
discussions.



10.  CONTACT

name:     David H. Crocker;
work      <email:  dcrocker@sgi.com;
          org:     Silicon Graphics, Inc.;
          street:  2011 N. Shoreline Blvd.;
          box:     7311;
          geo:     Mountain View / CA / US;    code: 94039-7311;
          phone:   +1 415 390 1804;          fax: +1 415 962 8404>























D. Crocker                                                       5