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Versions: 00 01 02 03 04 rfc3382                                        
INTERNET-DRAFT                                              Roger deBry
<draft-ietf-ipp-collection-02.txt>            Utah Valley State College
                                                             T. Hastings
                                                       Xerox Corporation
                                                              R. Herriot
                                                       Xerox Corporation
                                                                 K. Ocke
                                                       Xerox Corporation
                                                               P. Zehler
                                                       Xerox Corporation
                                                           March 9, 2000

                   Internet Printing Protocol (IPP):
                   The 'collection' attribute syntax

    Copyright (C) The Internet Society (2000). All Rights Reserved.


Status of this Memo:

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of [RFC2026].  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups.  Note that other groups may also distribute working
documents as Internet-Drafts.


Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress".


The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt


The list of Internet-Draft Shadow Directories can be accessed as
http://www.ietf.org/shadow.html.

                                Abstract

   This document specifies an OPTIONAL attribute syntax called
   'collection' for use with the Internet Printing Protocol/1.0
   (IPP) [RFC2565, RFC2566], IPP/1.1 [ipp-mod, ipp-pro], and
   subsequent versions. A 'collection' is a container holding one or
   more named values, which are called "member" attributes.  A
   collection allows data to be grouped like a PostScript dictionary
   or a Java Map.

   There are 4 issues in the document.








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The full set of IPP documents includes:

  Design Goals for an Internet Printing Protocol [RFC2567]
  Rationale for the Structure and Model and Protocol for the Internet
     Printing Protocol [RFC2568]
  Internet Printing Protocol/1.1: Model and Semantics (this document)
  Internet Printing Protocol/1.1: Encoding and Transport [IPP-PRO]
  Internet Printing Protocol/1.1: Implementer's Guide [IPP-IIG]
  Mapping between LPD and IPP Protocols [RFC2569]


The "Design Goals for an Internet Printing Protocol" document takes a
broad look at distributed printing functionality, and it enumerates
real-life scenarios that help to clarify the features that need to be
included in a printing protocol for the Internet.  It identifies
requirements for three types of users: end users, operators, and
administrators.  It calls out a subset of end user requirements that are
satisfied in IPP/1.0.  A few OPTIONAL operator operations have been
added to IPP/1.1.


The "Rationale for the Structure and Model and Protocol for the Internet
Printing Protocol" document describes IPP from a high level view,
defines a roadmap for the various documents that form the suite of IPP
specification documents, and gives background and rationale for the IETF
working group's major decisions.


The "Internet Printing Protocol/1.1: Encoding and Transport" document is
a formal mapping of the abstract operations and attributes defined in
the model document onto HTTP/1.1 [RFC2616].  It defines the encoding
rules for a new Internet MIME media type called "application/ipp".  This
document also defines the rules for transporting over HTTP a message
body whose Content-Type is "application/ipp".  This document defines a
new scheme named 'ipp' for identifying IPP printers and jobs.


The "Internet Printing Protocol/1.1: Implementer's Guide" document gives
insight and advice to implementers of IPP clients and IPP objects.  It
is intended to help them understand IPP/1.1 and some of the
considerations that may assist them in the design of their client and/or
IPP object implementations.  For example, a typical order of processing
requests is given, including error checking.  Motivation for some of the
specification decisions is also included.


The "Mapping between LPD and IPP Protocols" document gives some advice
to implementers of gateways between IPP and LPD (Line Printer Daemon)
implementations.









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                           Table of Contents

1  Problem Statement.................................................4
2  Solution..........................................................4
3  Definition of a Collection Attribute..............................5
 3.1 Member Attribute Naming Rules..................................5
 3.2 Remaining rules for a collection attribute definition..........6
 3.3 Nested Collections.............................................8
 3.4 Collection Attributes as Operation Attributes..................9
 3.5 Collections as Job Template Attributes.........................9
 3.6 Collections and Get-Printer-Attributes and Get-Job-Attributes
 operations.........................................................10
4  New Out-of-band value............................................11
 4.1 'none'........................................................11
5  Unsupported Values...............................................12
6  Sample specification.............................................12
7  Encoding.........................................................13
 7.1 encoding of a collection (using solution 1a)..................17
 7.2 Sample Encoding (using solution 1a)...........................19
 7.3 1setOf Collection encoding (using solution 1a)................20
 7.4 Sample 1setOf Collection encoding (using solution 1a).........21
8  Legacy issues....................................................23
9  IANA Considerations..............................................24
10 Internationalization Considerations..............................24
11 Security Considerations..........................................24
12 References.......................................................24
13 Author's Addresses...............................................25
14 Appendix A: Full Copyright Statement.............................26


























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1  Problem Statement


The IPP Model and Semantics [ipp-mod] supports most of the common data
structures that are available in programming languages. It lacks a
mechanism for grouping several attributes of different types.  The Java
language uses the Map to solve this problem and PostScript has a
dictionary.  The new mechanism for grouping attributes together must
allow for optional members and subsequent extension of the collection.


The mechanism must be encoded in a manner consistent with existing 1.0
and 1.1 parsing rules (see [ipp-pro]).  Current 1.0 and 1.1 parsers that
don't support collections should not confuse collections they receive
with attributes that they do support.


2  Solution


The new mechanism is a new IPP attribute syntax called a 'collection'.
As such each collection value is a value of an attribute whose attribute
syntax type is defined to be a 'collection'.  Such an attribute is
called a collection attribute.  The name of the collection attribute
serves to identify the collection value in an operation request or
response, as with any attribute value.

The 'collection' attribute syntax is a container holding one or more
named values (i.e., attributes), which are called member attributes.
Each collection attribute definition document lists the mandatory and
optional member attributes of each collection value. A collection value
is similar to an IPP attribute group in a request or a response, such as
the operation attributes group. They both consist of a set of
attributes.

As with any attribute syntax, the collection attribute definition
document specifies whether the attribute is single-value (collection) or
multi-valued (1setOf collection).

The name of each member attribute MUST be unique, but MAY be the same as
the name of a member attribute in another collection type and/or MAY be
the same as the name of an attribute that is not a member of a
collection..  The rules for naming member attributes are given in
section 3.1.

Each member attribute can have any attribute syntax type, including
'collection', and can be either single-valued or multi-valued.  The
length of a collection value is not limited. However, the length of each
member attribute MUST NOT exceed the limit of its attribute syntax.

The member attributes in a collection MAY be in any order in a request
or response. When a client sends a collection attribute to the Printer,


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the order that the Printer stores the member attributes of the
collection value and the order returned in a response MAY be different
from the order sent by the client.

A collection value MUST NOT contains two or more member attributes with
the same attribute name.  Such a collection is mal-formed.  Clients MUST
NOT submit such malformed requests and Printers MUST NOT return such
malformed responses.  If such a malformed request is submitted to a
Printer, the Printer MUST reject the request with the 'client-error-bad-
request' status code (see section 13.1.4.1)

ISSUE 01:  In attribute groups [ipp-mod] allows a Printer either (1) to
reject a request with duplicate named attributes OR (2) to choose
exactly one of the attributes as the one to be used.  Should we REQUIRE
the Printer to reject duplicate named attributes in a collection value
as stated above or allow the Printer to choose one member attribute as a
second alternative as we do with attribute groups?


3  Definition of a Collection Attribute


This section describes the requirements for any collection attribute
definition.


3.1 Member Attribute Naming Rules

Each collection attribute MUST have a unique name within the scope in
which the collection attribute occurs.  If the collection attribute
occurs as a member of a request or response attribute group, it MUST be
unique within that group, same as for any other attribute.  If a
collection attribute occurs as a member attribute of another collection,
the collection attribute MUST have a unique name within that collection
value, same as for any other attribute.

Each member attribute in a collection value MUST have unique name within
that collection value.  Member attribute names MAY be reused between
different collection attributes.  An example is the "media" attribute
which MAY be used as a job template attribute (see [ipp-mod]) and in a
collection.  All attribute names that are reused MUST have an identical
syntax.  All attribute names that are reused MUST have a similar
semantics.  The semantic difference MUST be limited to boundary
conditions and constraints placed on the reused attributes.  All
attributes that are not reused from elsewhere in the IPP model MUST have
a globally unique name.

Assume that it is desirable to extend IPP by adding a Job Template
attribute that allows the client to select the media by its properties,
e.g., weight, color, size, etc., instead of by name as the "media (type3
keyword | name) Job Template attribute in IPP/1.1 (see [ipp-mod]).  The
first rule is that the existing attribute MUST NOT be extended by adding
the 'collection' attribute syntax to the existing "media" attribute.
That would cause too many interoperability problems and complicates the


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validation and defaulting rules as well.  Instead, a new attribute will
be defined with a suffix of "-col" (for collection), e.g., "media-col"
(collection).

For a second example, suppose it is desirable to extend IPP by allowing
the client to select the media for the job start sheet.  Again, this
would not be done by adding the 'collection' attribute syntax to the
existing "job-sheets" (type2 keyword | name) Job Template attribute.
Instead, a new "job-sheet-col" (collection) Job Template attribute MUST
be introduced.  The member of the "job-sheet-col" collection might be:

     "job-sheet-format" (type3 keyword | name)
     "media" (type3 keyword | name)

if any of the "media-supported" (1setOf (type3 keyword | name)) Printer
attribute values could be specified for job sheets.  The reason that the
"job-sheet-format" member attribute isn't named simply, "job-sheet", is
because its values only indicate the format, and don't imply any media,
while the "job-sheets" (type2 keyword | name) Job Template attribute do
imply a media.  This example illustrates when a member attribute can be
the same as another attribute (in this case a Job Template attribute)
and when the member attribute MUST have a different name.

If the definers of the "job-sheet-col" (collection) attribute intended
that the System Administrator be allowed to have a different set of
media values for job sheets than documents, then the definition document
for the "job-sheet-col" collection attribute would have the following
member attributes instead:

     "job-sheet-format" (type3 keyword | name)
     "job-sheet-media" (type3 keyword | name)

Then the supported values would be include in a separate "job-sheet-
media-supported" (1setOf (type3 keyword | name)) Printer attribute.


3.2 Remaining rules for a collection attribute definition

When a specification document defines an "xxx" collection attribute,
i.e., an attribute whose attribute syntax type is 'collection' or
'1setOf collection'; the definition document MUST include the following
aspects of the attribute semantics.  Suppose the "xxx" collection
attribute contains an "aaa" member attribute.  A simplified example of a
collection specification is given in section 6

  1. The name of the collection attribute MUST be specified.  (e.g.
     "xxx")

  2. The collection attribute syntax MUST be of type 'collection' or
     '1setOf collection'.

  3. The context of the collection attribute MUST be specified, i.e.,
     whether the attribute is an operation attribute, a Job Template
     attribute, a Job Description attribute, a Printer Description



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     attribute, a member attribute of a particular collection attribute,
     etc.

  4. The member attributes MUST be defined.  For each member attribute
     the definition document MUST provide the following:

     a)The member attribute's name, "aaa", MUST either (1) reuse the
       attribute name of another attribute if the member attribute
       shares the syntax and semantics with the other attribute or (2)
       be unique across the entire IPP attribute name space

     b)Whether the member attribute is REQUIRED or OPTIONAL for the
       Printer to support

     c)Whether the member attribute is REQUIRED or OPTIONAL for the
       client to supply in a request

     d)The member attribute's syntax type, which can be any attribute
       syntax, including '1setOf X', 'collection', and '1setOf
       collection'.  If this attribute name is the same as another
       attribute (case of option a-1 above), it MUST have the same
       attribute syntax, including cardinality (1setOf or not).

     e)The semantics of the "aaa" member attribute. The semantic
       definition MUST include a description of any constraint or
       boundary conditions the member attribute places on the
       associated attribute, especially if the attribute is the same as
       another attribute used in a different context (case of option a-
       1 above)

     f)the supported values for the "aaa" member attribute, either
       enumerated explicitly or specified by the values of a referenced
       attribute which may be specified by either:

          @ the attribute's definition

          @ a Printer attribute, such as "aaa-supported", which
            contains the explicit values supported. The "aaa-supported"
            attribute is a Printer attribute and not in a collection.
            For example, if a collection contains the "media" attribute
            and its supported values are specified by the "media-
            supported" attribute, the "media-supported" attribute is
            the same Printer attribute that the "media" attribute uses.

     g)the default value of "aaa" member attribute if it is OPTIONAL
       for a client to supply the "aaa" member attribute in a request.
       The default value is specified by either:

          @ the attribute's definition

          @ a Printer attribute, such as "aaa-default", which may have
            a collection value


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          @ or an implementation defined algorithm that takes into
            account the values of the other member attributes of the
            collection value

     h)Depending on the collection attributes context, it MUST follow
       the additional rules specified below for the various contexts.


3.3 Nested Collections

A member attribute may have a syntax type of 'collection' or '1setOf
collection'. The following example assumes a "yyy" collection attribute
is a member attribute of the preceding "xxx" collection attribute.   The
"yyy" collection attribute contains "bbb" member attribute.   The
definition document for the nested collection MUST include:

1.The name of the collection attribute, e.g., "yyy"

2.The collection attribute syntax MUST be of type 'collection' or
  '1setOf collection'

3.The member attributes MUST be defined.  For each member attribute the
  definition document MUST provide the following:

  a) The member attribute's name, "bbb", MUST either (1) reuse the
     attribute name of another attribute if the member attribute shares
     the syntax and semantics with the other attribute or (2) be unique
     across the entire IPP attribute name space

  b) Whether the member attribute is REQUIRED or OPTIONAL for the
     Printer to support

  c) Whether the member attribute is REQUIRED or OPTIONAL for the client
     to supply in a request

  d) The member attribute's syntax type, which can be any attribute
     syntax, including '1setOf X', 'collection', and '1setOf
     collection'.  If this attribute name is the same as another
     attribute (case of option a-1 above), it MUST have the same
     attribute syntax, including cardinality (1setOf or not)

  e) The semantics of the member attribute. The semantic definition MUST
     include a description of any constraint or boundary conditions the
     member attribute places on the associated attribute, especially if
     the attribute is the same as another attribute used in a different
     context (case of option a-1 above)

  f)

  g) Depending on the collection attributes context, it MUST follow the
     additional rules specified below for the various contexts.




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3.4 Collection Attributes as Operation Attributes

The definition documents that define a collection attribute for use as
an operation attribute MUST follow these additional rules:

    a)Define in which operation requests the collection attribute is
      intended to be used.

    b)Define in which operation responses the collection attribute is
      intended to be used.


3.5 Collections as Job Template Attributes

The definition documents for collection attributes that are specified to
be Job Template attributes (see [ipp-mod] section 4.2) MUST have
associated printer attributes with suffixes of "-supported" and "-
default" (or indicate that there is no "-default"), just as for any Job
Template attribute.  Certain Job Template collection attributes also
have an associated Printer attribute with "-ready" (for example, see the
"media-ready" attribute in [ipp-mod]).  Furthermore member attributes of
job template attributes are addressed using the same suffix convention.

See also section 3.6 on the interaction of collections and the Get-
Printer-Attributes and Get-Jobs-Attributes.

For the following rules assume the "xxx" (collection) example from
section 3.2 is a job template attribute.

1)There MUST be two associated printer attributes.  The attributes are
  "xxx-supported" and "xxx-default"

2)The "xxx-default" is a collection with a syntax identical to the
  "xxx" specification in section 3.2 .

     @ Each member attribute has the same name as in the "xxx"
       definition.

     @ A Get-Printer-Attributes operation MUST return the "xxx-default"
       (collection) Printer attribute and all the member attributes.
       Any default values that have been set MUST be returned.  Any
       default values that have not been set MUST return an out of band
       attribute of 'no-value'.

3.If the definition of the collection does not mention an "xxx-ready"
  attribute than it is assumed that one is not defined, though
  implementer's are free to support an "xxx-ready" as an extension.

4.The collection attribute definition document MUST define an "xxx-
  supported" attribute with either a syntax of '1setOf type2 keyword'
  or '1setOf collection':




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     @ If the definition uses the '1setOf type2 keyword' attribute
       syntax, it MUST be the attribute keyword names of all of the
       member attributes that the Printer implementation supports in a
       Job Creation operation.  Furthermore, the definition MUST
       include corresponding definitions of each of the "aaa-supported"
       attributes that correspond to each "aaa" member attribute.  Then
       a client can determine the supported values of each member
       attribute in the Job Template collection attribute

     @ If the definition uses the '1setOf collection' attribute syntax,
       then the values are the supported instances of the "xxx"
       (collection) attribute that a client can supply in a Job
       Creation operation.  It is expected that this second approach
       will be used for small collections whether the number of
       possible collection values is small.  For example, a "media-
       size" (collection) member attribute in which the member
       attributes are "x-dimension" (integer) and "y-dimension"
       (integer). The pairs of integers are just like keywords as far
       as the client localization is concerned, except that if the
       client doesn't recognize a size pair of numbers, it can display
       the numbers.

  a) The keywords returned lists all the contained member attribute
     names.  This example would return the "aaa" keyword.

  b) The list is recursive and lists all the member attributes of the
     contained collections. In section 3.3 the printer would return
     "aaa" and "bbb" for collection "xxx"

  c) The encoding convention allows the reconstruction of the collection
     structure. The will allow the client to reconstruct the
     collections.  The client would know that "aaa" is a member of
     collection "xxx".  It can also be derived that collection "bbb" is
     a member of collection "yyy".  See section 7 for more information
     on encoding.

  d) To obtain the supported values for any member attribute a client
     performs a Get-Printer-Attributes operation explicitly requesting
     the member attribute name with the suffix "supported".  If a member
     attribute is itself a collection rule 4 above applies to member
     attribute.


3.6 Collections and Get-Printer-Attributes and Get-Job-Attributes
    operations

The behavior of collections for "job-description" and "printer-
description" is similar to any other attribute.  Simple attributes
return the attribute and its value.  For a collection, the collection
and its entire member attributes and their values are returned.  This
includes any containing collections, its member attributes and their
values.  The same logic applies for the "-default" and "-ready" printer
attribute associated with a job-template attributes.


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Whether the Printer applies individual member attributes independently
or takes into account the member attributes supplied by the client in
the collection, depends on implementation.  Therefore, a client SHOULD
query the Printer's "xxx-default" (collection) attribute, allow the user
to make any changes, and then submit the entire collection to the
Printer.  Then the variability in defaulting between different
implementations will not cause the user to get unexpected results.

The semantics for "-supported" is different for a collection.  Here the
focus is on the member attributes that the collection supports.  This
solution allows for extension of collections and allowing the member
attributes of a collection to vary (i.e. mandatory and optional member
attributes).  Once a client determines what member attributes are
supported in a collection a subsequent request can be constructed to
determine the supported values for the member attributes.

Another advantage of that the behavior of the "-supported" printer
collection attribute is limiting the amount of data that is returned on
general queries.  A 'get-printer-attributes' that returns all the
attributes of a printer will not have to return what may turn out to be
extensive lists of "-supported" attribute values.  An example might be
"media-col" that could be a representation for media using a collection
that goes beyond the information currently provided by the job-template
attribute "media".  The "media-col" could now be used to represent a
job's media, insert sheets and inserted tab sheets.  An IPP Printer
implementation would return the member attributes for each of the "-
supported" collections.


4  New Out-of-band value


4.1 'none'

'none'   The specified Job Template attribute in the request MUST
          NOT be applied to the job.  Specifically, this value
          overrides the Printer's "xxx-default" attribute value for
          the Job Template attribute, if one exists.


This "out-of-band" value allows a client to specify "turn-off" a feature
that is specified by an attribute whose value is a collection. Because a
client specifies a value, the Printer uses the client-specified value
and not the Printer's default value.


If a Printer supports the use of the 'collection' attribute syntax for
an attribute, a Printer MUST support the use of the "out-of-band" value
'none'.


A Printer MUST support the "out-of-band" value 'none' as the value for
an attribute "xxx" if:




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     @ the definition of the attribute specifies 'none' MUST be
       supported AND


     @ the definition of the attribute specifies 'none' MAY be
       supported and it is a value of the attribute "xxx-supported".


5  Unsupported Values


The rules for returning an unsupported collection attribute are an
extension to the current rules.

   If the entire collection attribute is unsupported, then the Printer
   returns just the collection attribute name with the 'unsupported'
   out-of-band value (see the beginning of [ipp-mod] section 4.1) in the
   Unsupported Attributes Group.

   If a collection contains unrecognized, unsupported member attributes
   and/or conflicting values, the attribute returned in the Unsupported
   Group is a collection containing the unrecognized, unsupported member
   attributes, and/or conflicting values. The unrecognized member
   attributes have an out-of-band value of 'unsupported' (see the
   beginning of [ipp-mod] section 4.1). The unsupported member
   attributes and conflicting values have their unsupported or
   conflicting values.


6  Sample specification


This example is for a collection called "media-col".  The "media-col"
attribute is a job template attribute.  This collection is simplified
and fictitious and is used for illustrative purposes only.

Name: media-col

Syntax: collection

Member Attributes:

     Name: "media-color"

     Syntax: type3 keyword | name

     Mandatory

     Semantics: This attribute identifies the color of the media.  Valid
     values are "red" "white" and "blue"

     "media-color-supported" syntax: 1setOf (type2 keyword | name)

     Name: "media-size"



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     Syntax: collection

     Member Attributes:

          Name: "x-dimension"

          Syntax: integer

          Mandatory

          Semantics: This attribute identifies length of the media in
          inches.  Valid values are any integer though in practice
          implementation will constrain the range.

          x-supported syntax: rangeOfInteger

          Name: "y-dimension"

          Syntax: integer

          Mandatory

          Semantics: This attribute identifies the width of the media in
          inches.  Valid values are any integer though in practice
          implementation will constrain the range.

          y-supported syntax: rangeOfInteger

     Name: name

     Syntax: See job template attribute "media"

     Optional

     Semantics: See job template attribute "media".  Additional
     restrictions on "media" in this collection are that the "media"
     value must be valid based on the size and color.  When invalid
     names are given based on the size or color, the size or color value
     takes precedence.

     Supported values identical to job template attribute "media-
     supported".




7  Encoding


This section is still under construction.

We are now down to considering two encodings for collections. The goals
of the encoding are:


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   a) must be simple

   b) a legacy receiver must correctly ignore a collection value and not
incorrectly decode part of a collection as a legitimate attribute.

   c) it parses an attributes with collection values as a single unknown
attribute rather than as many unknown attributes.

The two encodings are:

     1) encode attributes within collections in the same way as
     attributes outside of collections, but encode each attribute name
     in a collection so that its name cannot be the same as an attribute
     name outside of a collection. We have considered two solutions for
     encoding attribute names.

          a) add a prefix to each collection member attribute name where
          the prefix is the (outer) attribute's name following by a dot
          ("."). Nested collections have extra levels of dotted names.
          For example, the "media-size" attribute in "media-col" is
          encoded as "media-col.media-size" and the "x" attribute in
          "media-size" which is inside "media" is encoded as "media-
          col.media-size.x". The outer attribute name is the "name" of
          the begin-collection and end-collection value.

          b) add a hyphen suffix to each attribute name in a collection.
          For example, the "media-size" attribute in "media-col" is
          encoded as "media-size-" and the "x" attribute in "media-size"
          which is inside "media" is encoded as "x-". Note the hyphen
          must be a suffix so that the attribute name follows the rules
          for a legal keyword, and the hyphen is chosen because no
          attributes currently end with a hyphen. The empty name is used
          for the  end-collection value and all but the first begin-
          collection value.

     2) encode attributes within a collection as a 1setOf values where
     each attribute whose name is M and whose values are V1 ... Vn are
     encoded as a sequence of n+1 values M, V1, ... Vn. Subsequent
     member attributes continue the value in the 1setOf values.

The following are examples of encodings. In the real encoding, each
"attribute" consists of

    a) a one byte tag

    b) a two byte name length whose value is "n"

    c) "n" bytes of a name

    d) a two bytes value length whose value is "v"

    e) "v" bytes of a value


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To make it easy to read, we show only items c (the name), a (the tag)
and e (the value), in that order.

There are 3 encoding examples for each solution:

   i) media-col with media-color and media-size as member attributes,
and where media-size contains "x" and "y" as collection members.

   ii) media-size-supported with two collection values.

   iii) job-notify with notify-recipients and notify-events which is a
1setOf keyword with 3 values in this example

Solution 1a)



      Name                           syntax-type            value
      "media-col"                    begin-collection       ""
      "media-col.media-color"        keyword                white
      "media-col.media-size"         begin-collection       ""
      "media-col.media-size.x"       integer                850
      "media-col.media-size.y"       integer                1100
      "media-col.media-size"         end-collection         ""
      "media-col"                    end-collection         ""

      Name                           syntax-type            value
      "media-size-supported"         begin-collection       ""
      "media-size-supported.x"       integer                850
      "media-size-supported.y"       integer                1100
      "media-size-supported"         end-collection         ""
      "media-size-supported"         begin-collection       ""
      "media-size-supported.x"       integer                850
      "media-size-supported.y"       integer                1400
      "media-size-supported"         end-collection         ""

      Name                           syntax-type            value
      "job-notify"                   begin-collection       ""
      "job-notify.notify-recipients" url       "mailto://bill@foo.com"
      "job-notify.notify-events"     keyword             job-completed
      ""                             keyword               job-created
      ""                             keyword         job-state-changed
      "job-notify"                   end-collection         ""


Solution 1b)

      Name                           syntax-type            value
      "media-col"                    begin-collection       ""
      "media-color-"                 keyword                white
      "media-size-"                  begin-collection       ""
      "x-"                           integer                850
      "y-"                           integer                1100

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      "media-size-"                  end-collection         ""
      ""                             end-collection         ""

      Name                           syntax-type            value
      "media-size-supported"         begin-collection       ""
      "x-"                           integer                850
      "y-"                           integer                1100
      ""                             end-collection         ""
      ""                             begin-collection       ""
      "x-"                           integer                850
      "y-"                           integer               1400
      ""                             end-collection         ""

      Name                           syntax-type            value
      "job-notify"                   begin-collection      ""
      "notify-recipients-"           url      "mailto://bill@foo.com"
      "notify-events-"               keyword          "job-completed"
      ""                             keyword            "job-created"
      ""                             keyword      "job-state-changed"
      "job-notify"                   end-collection        ""


Solution 2)

       Name                          syntax-type               value
       "media-col"                   begin-collection             ""
       ""                            attribute-name    "media-color"
       ""                            keyword                   white
       ""                            attribute-name     "media-size"
       ""                            begin-collection             ""
       ""                            attribute-name              "x"
       ""                            integer                     850
       ""                            attribute-name              "y"
       ""                            integer                    1100
       ""                            end-collection               ""
       ""                            end-collection               ""

      Name                           syntax-type               value
      "media-size-supported"         begin-collection             ""
      ""                             attribute-name              "x"
      ""                             integer                     850
      ""                             attribute-name              "y"
      ""                             integer                    1100
      ""                             end-collection               ""
      ""                             begin-collection             ""
      ""                             attribute-name              "x"
      ""                             integer                     850
      ""                             attribute-name              "y"
      ""                             integer                    1400
      ""                             end-collection               ""

      Name                           syntax-type               value


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      "job-notify"                   begin-collection             ""
      ""                             attribute-name "notify-recipients"
      ""                             url       mailto://bill@foo.com"
      ""                             attribute-name   "notify-events"
      ""                             keyword          "job-completed"
      ""                             keyword            "job-created"
      ""                             keyword      "job-state-changed"
      ""                             end-collection                ""




Observations:

Solution 1a have identical properties to solution 1b except that the
rules for encoding the name are more complicated for 1a, and the name of
the attribute appears before each end-collection and end-collection in
1a but only before the first begin-collection in 1b.

If a collection aware client sends a collection to a collection unaware
Printer:

For solutions 1a and 1b)  the Printer sees many attributes in place of
the collection and it returns in the Unsupported attribute group, all of
the attributes: the attribute outside the collection and each attribute
in the collection with it altered name. Thus the unsupported attributes
have names that the client didn't send and they may be in an order that
makes it hard to reconstruct the collection. In addition, because the
"end-collection" has the same name as the attribute for 1a, some
printers will reject the job because the attribute appears twice. Also,
1a does not work for a 1setOf collection because the name of the
attributes appear in front of each begin-collection and thus cannot be
distinguished from two occurrences of the same attribute.

For solution 2) the Printer sees the collection as a 1setOf values where
some values have unknown syntax types and other values have known syntax
types.  When a collection-unaware printer discovers it doesn't
understand an attribute that is a collection,  it sees the unknown
attribute as a 1setOf rather than a collection. It still returns the
attribute-name with the out-of-band value "unsupported" making it easier
for the client.




7.1 encoding of a collection (using solution 1a)

NOTE:  If we pick another solution to the encoding, this section will
change.

Each collection MUST have a globally unique name.  Each attribute in an
attribute group or a collection MUST have globally unique name.



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Uniqueness is generated by prepending the collection name to the
attribute using a period, '.' as a separator.

For encoding attributes that have a 'collection' attribute syntax, the
attribute's name is REQUIRED to be the first part of each of the member
attribute name separated by a PERIOD (.) character.  For example, if a
"media-col" (collection) Job Template attribute is added to IPP and
contains a member attribute "color, it  MUST be encoded as a "media-
col.color".  In another example, if the "job-sheets" (collection) Job
Template attribute is added to IPP and reuses the "color" member
attribute, the "color" attribute MUST be encoded as "job-sheets.color".
The "xxx.color" attribute has an identical attribute syntax and similar
semantics.

When encoding a collection attribute "xxx" that contains an attribute
"aaa".  A simplified example of a collection specification is given in
section 6

1.The beginning of the collection is indicated with a value tag that
  MUST be syntax type 'begincollection' (e.g. 0x34).

2.The length of the collection name (e.g. 0x03)

3.The collection name (e.g. "xxx")

4.A null collection value length (e.g. 0x00)

5.The attributes are encoded as with any other attribute.  It is valid
  to have a collection a member of a collection.  The modifications
  necessary for encoding member attributes of a collection are as
  follows.

  a) The name of the member attribute MUST be prepended with the
     collection name and a period.

  b) The length of the member attribute name MUST be adjusted
     appropriately.

6.The end of the collection is indicated with a value tag that MUST be
  syntax type 'endCollection' (e.g. 0x37).

7.The length of the collection name (e.g. 0x03)

8.The collection name (e.g. "xxx")

9.A null collection value length (e.g. 0x00)








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7.2 Sample Encoding (using solution 1a)

NOTE:  If we pick another solution to the encoding, this section will
change.

This section defines the encoding of a collection syntax type using
solution 1a.  The collection specified in section 6 is used.  The
encoding is of an implementation that does not support any optional
attributes.  A collection is encoded by using two new tags:

Tag name         Tag      Meaning
                 value

beginCollection  0x34     Begin the named collection.

endCollection    0x37     End the named collection.

 A collection value is encoded as a sequence of attribute values
preceded by a beginCollection attribute and followed by an endCollection
attribute. The name field of a beginCollection and an endCollection both
contain the name of the collection type, i.e., the keyword name of the
collection attribute, which is a string of ASCII characters. The value
field contains the prefix used for all subordinate member attributes.
The following example is written in the style of the IPP/1.1 "Encoding
and Transport" document [ipp-pro].  The following example is for a media
collection attribute.  The media collection contains 2 member
attributes.  One member is "color" that contains a keyword for the
media's color.  The second attribute is a collection that gives the
media's size.  The size collection has two integer attributes "x" and
"y" that gives the media's size in inches

Octets           Symbolic       Protocol   comments
                 Value          field

0x34             beginCollecti  value-tag  Beginning of the collection
                 on
0x0009                          name-      Length of collection's name
                                length
media-col        media-col      Name       Collection's name
0x0000                          Value-
                                length

0x44             keyword type   value-tag  Member attribute type
0x000F                          name-      Length of member attribute
                                length     name
media-col.color  media-         Name       Name of member attribute
                 col.color
0x0004                          value-
                                length
blue             blue           Value

0x34             beginCollecti  value-tag  Beginning of the sub-
                 on                        collection


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Octets           Symbolic       Protocol   comments
                 Value          field

0x000E                          name-      Length of sub-collection's
                                length     name
media-col.size   media-         Name       Sub-collection's name
                 col.size
0x0000                          Value-
                                length

0x21             integer type   value-tag  Member attribute type
0x0010                          name-      Length of member attribute
                                length     name
media-           media-         Name       Name of member attribute
col.size.x       col.size.x
0x0004                          value-
                                length
0x0006                          Value

0x21             integer type   value-tag  Member attribute type
0x0007                          name-      Length of member attribute
                                length     name
media-           media-         Name       Name of member attribute
col.size.y       col.size.y
0x0004                          value-
                                length
0x0004                          Value

0x37             endCollection  value-tag  end of the sub-collection
0x0007                          name-      Length of sub-collection's
                                length     name
media-col.size   media-         Name       Sub-collection's name
                 col.size
0x0000                          Value-
                                length

0x37             endCollection  value-tag  end of the collection
0x0007                          name-      Length of collection's name
                                length
media-col        media-col      Name       Sub-collection's name
0x0000                          Value-
                                length



7.3 1setOf Collection encoding (using solution 1a)

The encoding of a set of collections follows the standard method of
encoding multi-valued IPP attributes.  The "beginCollection" attribute
is coded normally.  The first instance of the collection follows.  The
"endCollection" MUST appear only once in a collection and MUST follow
the last member of the set of collection.  The member collections of a


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set of collections are delineated by a specially encoded
"beginCollection" attribute.  The type MUST be "beginCollection" (i.e.
0x34).  The length of the name field MUST be 0x0000.  The name field
MUST be omitted.  The length of the value MUST be the length of the
collection's prefix.  The value MUST be the prefix.


7.4 Sample 1setOf Collection encoding (using solution 1a)

NOTE:  If we pick another solution to the encoding, this section will
change.

This section defines the encoding of a collection syntax type using
solution 1a.  The collection specified in section 7 is used.  The
difference is that the type of "media-col" is 1setOf collection instead
of collection.  The encoding is of an implementation that does not
support any optional attributes.



Octets           Symbolic       Protocol   comments
                 Value          field

0x34             beginCollecti  value-tag  Beginning of the collection
                 on
0x0009                          name-      Length of collection's name
                                length
media-col        media-col      Name       Collection's name
0x0000                          Value-
                                length

0x44             keyword type   value-tag  Member attribute type
0x000F                          name-      Length of member attribute
                                length     name
media-col.color  media-         Name       Name of member attribute
                 col.color
0x0004                          value-
                                length
blue             blue           Value

0x34             beginCollecti  value-tag  Beginning of the sub-
                 on                        collection
0x000E                          name-      Length of sub-collection's
                                length     name
media-col.size   media-         Name       Sub-collection's name
                 col.size
0x0000                          Value-
                                length

0x21             integer type   value-tag  Member attribute type
0x00010                         name-      Length of member attribute
                                length     name



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Octets           Symbolic       Protocol   comments
                 Value          field

media-           media-         Name       Name of member attribute
col.size.y       col.size.y
0x0004                          value-
                                length
0x0006                          Value

0x21             integer type   value-tag  Member attribute type
0x00010                         name-      Length of member attribute
                                length     name
media-           media-         Name       Name of member attribute
col.size.x       col.size.x
0x0004                          value-
                                length
0x0004                          Value

0x37             endCollection  value-tag  end of the sub-collection
0x000E                          name-      Length of sub-collection's
                                length     name
media-col.size   media-         Name       Sub-collection's name
                 col.size
0x0000                          Value-
                                length


                                           Second collection in set

0x34             beginCollecti  value-tag  Beginning of the collection
                 on
0x0000                          name-      Indicates continuation of
                                length     set
0x0000                          Value-
                                length

0x44             keyword type   value-tag  Member attribute type
0x000F                          name-      Length of member attribute
                                length     name
media-col.color  media-         Name       Name of member attribute
                 col.color
0x0003                          value-
                                length
red              red            Value

0x34             beginCollecti  value-tag  Beginning of the sub-
                 on                        collection
0x000E                          name-      Length of sub-collection's
                                length     name
media-col.size   media-         Name       Sub-collection's name
                 col.size



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Octets           Symbolic       Protocol   comments
                 Value          field

0x0000                          Value-
                                length

0x21             integer type   value-tag  Member attribute type
0x0010                          name-      Length of member attribute
                                length     name
media-           media-         Name       Name of member attribute
col.size.y       col.size.y
0x0004                          value-
                                length
0x0006                          Value

0x21             integer type   value-tag  Member attribute type
0x0010                          name-      Length of member attribute
                                length     name
media-           media-         Name       Name of member attribute
col.size.x       col.size.x
0x0004                          value-
                                length
0x0004                          Value

0x37             endCollection  value-tag  end of the sub-collection
0x000E                          name-      Length of sub-collection's
                                length     name
media-col.size   media-         Name       Sub-collection's name
                 col.size
0x0000                          Value-
                                length

0x37             endCollection  value-tag  end of the set of
                                           collections
0x0009                          name-      Length of collection's name
                                length
media-col        media-col      Name       collection's name
0x0000                          Value-     Length of collection's
                                length     prefix





8  Legacy issues


IPP 1.x Printers and Clients will gracefully ignore collections and its
member attributes if it does not understand the collection.  The
begCollection and endCollection elements each look like an attribute
with an attribute syntax that the recipient doesn't support and so
should ignore the entire attribute.  The individual member attributes
will look like ordinary attributes, but since they each are encoded with

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a unique name that can't be the same as a top level attribute, each of
the member attributes will also look like attributes that the recipient
doesn't support and so should ignore.


9  IANA Considerations


This attribute syntax will be registered with IANA after the WG approves
its specification according to the procedures for extension of the
IPP/1.1 Model and Semantics [ipp-mod].

ISSUE 04 - Since this is intended to be a standards track document, do
we also register the attribute syntax with IANA?


10 Internationalization Considerations


This attribute syntax by itself has no impact on internationalization.
However, the member attributes that are subsequently defined for use in
a collection may have internationalization considerations, as may any
attribute, according to [ipp-mod].


11 Security Considerations


This attribute syntax causes no more security concerns than any other
attribute syntax.  It is only the attributes that are subsequently
defined to use this or any other attribute syntax that may have security
concerns, depending on the semantics of the attribute, according to
[ipp-mod].


12 References

[ipp-mod]
     Isaacson, S., deBry, R., Hastings, T., Herriot, R., Powell, P.,
     "Internet Printing Protocol/1.1: Model and Semantics" draft-ietf-
     ipp-model-v11-06.txt, March 1, 2000.

[ipp-ntfy]
     Isaacson, S., Martin, J., deBry, R., Hastings, T., Shepherd, M.,
     Bergman, R. " Internet Printing Protocol/1.0 & 1.1:  IPP Event
     Notification Specification" draft-ietf-ipp-not-spec-02.txt, work in
     progress, February 2, 2000.

[ipp-pro]
     Herriot, R., Butler, S., Moore, P., Turner, R., "Internet Printing
     Protocol/1.1: Encoding and Transport", draft-ietf-ipp-protocol-v11-
     05.txt, March 1, 2000.

[RFC2565]
     Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
     Protocol/1.0: Encoding and Transport", RFC 2565, April 1999.

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[RFC2566]
     R. deBry, T. Hastings, R. Herriot, S. Isaacson, P. Powell,
     "Internet Printing Protocol/1.0: Model and Semantics", RFC 2566,
     April 1999.

[RFC2567]
     Wright, D., "Design Goals for an Internet Printing Protocol", RFC
     2567, April 1999.

[RFC2568]
     Zilles, S., "Rationale for the Structure and Model and Protocol for
     the Internet Printing Protocol", RFC 2568, April 1999.

[RFC2569]
     Herriot, R., Hastings, T., Jacobs, N., Martin, J., "Mapping between
     LPD and IPP Protocols", RFC 2569, April 1999.

[RFC2616]
     R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P.
     Leach, T. Berners-Lee, "Hypertext Transfer Protocol - HTTP/1.1",
     RFC 2616, June 1999.


13 Author's Addresses

     Roger deBry
     Utah Valley State College
     Orem, UT 84058
     Phone: (801) 222-8000
     EMail: debryro@uvsc.edu

     Tom Hastings
     Xerox Corporation
     737 Hawaii St.  ESAE 231
     El Segundo, CA  90245
     Phone: 310-333-6413
     Fax: 310-333-5514
     e-mail: hastings@cp10.es.xerox.com

     Robert Herriot
     Xerox Corp.
     3400 Hill View Ave, Building 1
     Palo Alto, CA 94304
     Phone: 650-813-7696
     Fax:  650-813-6860
     e-mail: robert.herriot@pahv.xerox.com

     Kirk Ocke
     Xerox Corp.
     800 Phillips Rd
     M/S 139-05A
     Webster, NY 14580


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     Phone: (716) 442-4832
     EMail: kirk.ocke@usa.xerox.com

     Peter Zehler
     Xerox Corp.
     800 Phillips Rd
     M/S 139-05A
     Webster, NY 14580
     Phone: (716) 265-8755
     EMail: peter.zehler@usa.xerox.com

14 Appendix A: Full Copyright Statement


Copyright (C) The Internet Society (1998,1999,2000). 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.
















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