INTERNET-DRAFT Roger deBry
<draft-ietf-ipp-collection-04.txt> Utah Valley State College
T. Hastings
Xerox Corporation
R. Herriot
Xerox Corporation
K. Ocke
Xerox Corporation
P. Zehler
Xerox Corporation
January 24, 2001
Internet Printing Protocol (IPP):
The 'collection' attribute syntax
Copyright (C) The Internet Society (2001). 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
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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 [RFC2911, RFC2910], 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. This document also specifies the conformance
requirements for a definition document that defines a collection
attribute. Finally, this document gives some illustrative
example collection attribute definitions that are not intended as
actual attribute specifications.
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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 [RFC2911]
Internet Printing Protocol/1.1: Encoding and Transport [RFC2910]
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 Introduction....................................................5
1.1 Problem Statement ............................................5
1.2 Solution .....................................................5
2 Terminology.....................................................6
2.1 Conformance Terminology ......................................6
2.2 Other terminology ............................................7
3 Definition of a Collection Attribute............................7
3.1 Information to Include .......................................7
3.2 Nested Collections ..........................................11
4 Collection Attributes as Attributes in Operations..............11
4.1 General Rules ...............................................11
4.2 Unsupported Values ..........................................11
5 Example definition of a collection attribute...................12
5.1 media-col (collection) ......................................12
5.1.1media-color (type3 keyword | name(MAX) ......................13
5.1.2media-size (collection) .....................................13
5.2 media-col-default (collection) ..............................14
5.3 media-col-ready (1setOf collection) .........................14
5.4 media-col-supported (1setOf type2 keyword) ..................14
6 A Second Example Definition Of A Collection Attribute..........15
7 Encoding.......................................................15
7.1 Additional tags defined for representing a collection attribute
value16
7.2 Example encoding: "media-col" (collection) ..................17
8 Legacy issues..................................................23
9 IANA Considerations............................................23
9.1 Attribute Syntax Registration ...............................23
10 Internationalization Considerations............................23
11 Security Considerations........................................24
12 References.....................................................24
13 Author's Addresses.............................................25
14 Appendix A: Encoding Example of a Simple Collection............26
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15 Appendix B: Encoding Example of 1setOf Collection..............29
16 Appendix C: Encoding Example of Collection containing 1setOf XXX
attribute.........................................................34
17 Appendix D: Full Copyright Statement...........................38
Table of Tables
Table 1 - "media-col" member attributes...........................13
Table 2 - "media-size" collection member attributes...............13
Table 3 - Tags defined for encoding the 'collection' attribute syntax
..............................................................16
Table 4 - Overview Encoding of "media-col" collection.............18
Table 5 - Example Encoding of "media-col" collection..............18
Table 6 - Overview Encoding of simple collection..................26
Table 7 - Example Encoding of simple collection...................26
Table 8 - Overview Encoding of 1setOf collection..................29
Table 9 - Example Encoding of 1setOf collection...................30
Table 10 - Overview Encoding of collection with 1setOf value......34
Table 11 - Example Encoding of collection with 1setOf value.......35
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1 Introduction
1.1 Problem Statement
The IPP Model and Semantics [RFC2911] 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
(called 'collection' mechanism) must allow for optional members and
subsequent addition of new members.
The 'collection' mechanism must be encoded in a manner consistent
with existing 1.0 and 1.1 parsing rules (see [RFC2910]). Current 1.0
and 1.1 parsers that don't support the 'collection' mechanism must
not confuse collections or parts of collection they receive with
other attributes.
1.2 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 document that defines a collection
attribute specifies whether the attribute is single-value
(collection) or multi-valued (1setOf collection). If the attribute is
multi-valued (1setOf collection) each collection value MUST be a
separate instance of a single definition of a collection, i.e. it
MUST have the same member attributes except for OPTIONAL member
attributes. If we view each collection definition as a separate
syntax type, this rule continues the IPP/1.1 notion that each
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attribute has a single type or pattern (e.g. "keyword | name" is a
pattern). Without this rule, the supported values would be more
difficult to describe and the mechanism defined in item 4 of section
3.1 would not be sufficient.
The name of each member attribute MUST be unique for a collection
attribute, but MAY be the same as the name of a member attribute in
another collection attribute 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, 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 (depending on
implementation) either (1) reject the request with the 'client-error-
bad-request' status code (see section 13.1.4.1), or (2) accept the
request and use only one of each duplicate member attribute.
2 Terminology
This section defines terminology used throughout this document.
2.1 Conformance Terminology
Capitalized terms, such as MUST, MUST NOT, REQUIRED, SHOULD, SHOULD
NOT, MAY, NEED NOT, and OPTIONAL, have special meaning relating to
conformance. These terms are defined in [RFC2911] section 12.1 on
conformance terminology, most of which is taken from RFC 2119
[RFC2119].
The following specialization of these terms apply to this document:
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REQUIRED: if an implementation supports the extensions described in
this document, it MUST support a REQUIRED feature.
OPTIONAL: if an implementation supports the extensions described in
this document, it MAY support an OPTIONAL feature.
2.2 Other terminology
This document uses terms such as Job object (or Job), IPP Printer
object (or Printer), "operation", "request", response", "attributes",
"keywords", and "support". These terms have special meaning and are
defined in the model terminology [RFC2911] section 12.2. The
following additional terms are introduced in this document:
collection: an attribute syntax in which each attribute value is a
set of attributes, called member attributes.
member attribute: an attribute that is defined to be used as one
of the attributes in a collection.
collection attribute: an attribute whose definition specifies the
'collection' attribute syntax and each of the member attributes
that MAY occur in a collection attribute value.
3 Definition of a Collection Attribute
This section describes the requirements for any collection attribute
definition.
3.1 Information to Include
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 N member attributes named "aaa1",
"aaa2", _, "aaaN" ("aaaI" represents any one of these N member
attributes).
1. The name of the collection attribute MUST be specified (e.g.
"xxx"). The selection of the name "xxx" MUST follow the same rules
for uniqueness as for attributes of any other syntax type (as
defined by IPP/1.1) unless "xxx" is a member attribute of another
collection. Then the selection of the name "xxx" MUST follow the
rules for uniqueness defined in item 5a) of this list.
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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
attribute, a member attribute of a particular collection attribute,
etc.
4. An "xxx-supported" attribute MUST be specified and it has one of
the following two forms:
a)"xxx-supported" is a "1setOf collection" which enumerates all of
the supported collection values of "xxx". If a collection of
this form contains a nested collection, it MUST be of the same
form.
For example, "media-size-supported" might have the values {{x-
dimension:210, y-dimension:297},{x-dimension:297, y-
dimension:420}} to show that it supports two values of "media
size": A4 (210x297) and A3 (297x420). It does not support other
combinations of "x-dimension" and "y-dimension" member
attributes, such as 210x420 or 297x297 and it does not supported
non-enumerated values, such as 420x595.
b)"xxx-supported" is a "1setOf type2 keyword" which enumerates
the names of all of the member attributes of "xxx": "aaa1",
"aaa2", _, "aaaN". If a collection of this form contains a
nested collection, it MAY be of either form. See item 5f) below
for details on supported values of member attributes.
For example, "media-col-supported" might have the keyword
values: "media-size" and "media-color".
5. The member attributes MUST be defined. For each member attribute
the definition document MUST provide the following information:
a)The member attribute's name (e.g., "aaa") MUST be unique within
the collection being defined and MUST either
i) reuse the attribute name of another attribute (that is unique
across the entire IPP attribute name space) and have the same
syntax and semantics as the reused attribute (if the condition
of item 4b) above is met). For example, a member attribute
definition could reuse the IPP/1.1 "media" attribute.
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ii) potentially occur elsewhere in the entire IPP attribute
name space. (if the condition of item 4a) above is met). For
example, a member attribute could be "x-dimension" which could
potentially occur in another collection or as an attribute
outside of a collection.
iii) be unique across the entire IPP attribute name space (if
the condition of item 4b) above is met). For example, a member
attribute could be "media-color" which must unique be 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 reuses the name of another
attribute (case of item a1 above), it MUST have the same
attribute syntax, including cardinality (whether or not 1setOf).
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 reuses the
name of another attribute (case of item a1 above)
f)The supported values for the each "aaaI" member attribute (of
the member attributes "aaa1", "aaa2", _, "aaaN") is specified
by one of two mechanisms.
i) If "xxx-supported" is a "1setOf collection" (see item 4a)
above), the value for each "aaaI" is specified in each
collection value of "xxx-supported" in the context of other
member attributes. That is, "xxx-supported" enumerates all
supported values of "xxx".
ii) If the value of "xxx-supported" is a "1setOf type2
keyword" (see item 4b) above), the supported values of "aaaI"
are the values specified by either i) the "aaaI-supported"
attribute or ii) the definition of the member attribute "aaaI"
within the document defining the "xxx" attribute. The values
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of each member attribute "aaaI" are specified independently of
other member attributes though a Printer is not required to
support all combinations of supported values.
For example, "media-col-supported" might have the keyword
values: "media-size" and "media-color". Using the first method
for defining supported values (an "aaaI-supported" attribute),
the collection values of "media-col" are combinations of
values of "media-size-supported" and "media-color-
supported".If "media-size-supported" has the values of
'210x297' and '297x420' and "media-color-supported" has the
values of 'white' and 'pink', the Printer might support only
the combinations 'white-210x297', 'pink-210x297'and 'white-
297x420', and not 'pink-297x420'.
If a collection contains a member "aaaI" whose syntax type is
"text", the supported values would probably be defined by the
definition of "xxx" rather than by the attribute "aaaI-
supported".
g)the default value of each "aaaI" member attribute if it is
OPTIONAL for a client to supply the "aaa" member attribute in a
request. The default value is specified by in the attribute's
definition within a document and MUST be one of the following:
i) a fixed default
ii) a mechanism by which the Printer determines default
iii) an indefinite default that is left to the implementation.
iv) an attribute that the Printer uses to determine the default
6. The default value of "xxx" if a client does not supply it. The
default value is specified by in the attribute's definition within
a document and MUST be one of the following:
a)a fixed default
b)a mechanism by which the Printer determines default
c)an indefinite default that is left to the implementation
d)a Printer attribute "xxx-default" which is a collection with the
same member attributes as "xxx". Though optional member
attributes may be absent in which case the Printer uses the
defaulting rules of item 5g) above.
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7. The "xxx-ready (1setOf collection)" attribute if human intervention
is required to make many of the supported values available. For
example, "media-col" is an attribute which has a "ready" attribute.
Most attributes do not have a "ready" attribute.
3.2 Nested Collections
A member attribute may have a syntax type of 'collection' or '1setOf
collection', in which case it is called a nested collection
attribute. The rules for a nested collection attribute are the same
as for a collection attribute as specified in section 3.1.
4 Collection Attributes as Attributes in Operations
4.1 General Rules
A collection value is like any other IPP/1.1 value, except that it is
structured. The rules for attributes with collection values are the
same as for attributes of any other syntax type (see IPP/1.1), be
they in any group of a request of a response.
4.2 Unsupported Values
The rules for returning an unsupported collection attribute are an
extension to the current rules:
1. 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 [RFC2911]
section 4.1) in the Unsupported Attributes Group.
2. 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 [RFC2911] section
4.1). The unsupported member attributes and conflicting values
have their unsupported or conflicting values.
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5 Example definition of a collection attribute
In some printing environments, it is desirable to allow the client to
select the media by its properties, e.g., weight, color, size, etc.,
instead of by name. In IPP/1.1 (see [RFC2911]), the "media (type3
keyword | name) Job Template attribute allows selection by name. It
is tempting to extend the "media" attribute syntax to include
"collection", but then existing clients could not understand default
or supported media values that use the collection value. To preserve
interoperability, a new attribute MUST BE added, e.g., "media-col
(collection)". The following subsections contain a sample definition
of a simplified "media-col" attribute. The definition follows the
rules in section 3.
All of the example attribute definitions in this document are
illustrative examples, rather than actual definitions. These
examples are intended to illustrate how to define collection
attributes. Other documents MUST define collection attributes for
use in actual interchange. Such definitions may be very similar to
the examples in this document, since we attempted to pick useful
examples.
Note: we picked the name "media-col" because the name "media" is
already in use. Ordinarily the collection attribute would have a name
like any other attribute and would not end in "col".
The member attributes of "media-col" attribute ("media-color (type 3
keyword)" and "media-size (collection)") both follow the naming rules
of item 4a3 of section 3, i.e. the names are unique across the entire
IPP attribute name space. The member attributes of the "media-size
(collection)" member attribute ("x-dimension (integer(0,MAX))" and
"y-dimension (integer(0,MAX))") both follow the naming rules of item
4a2 of section 3, i.e. they potentially occur elsewhere in the IPP
attribute name space.
5.1 media-col (collection)
The "media-col" (collection) attribute augments the IPP/1.1 [RFC2911]
"media" attribute. This collection attribute enables a client end
user to submit a list of media characteristics to the Printer. When
the client specifies media using the "media-col" collection
attribute, the Printer object MUST match the requested media exactly.
The 'collection' consists of the following member attributes:
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Table 1 - "media-col" member attributes
Attribute name attribute syntax reque Printer
st Support
media-color type3 keyword | name (MAX) MAY MUST
media-size collection MUST MUST
The definitions for the member attributes is given in the following
sub-sections:
5.1.1 media-color (type3 keyword | name(MAX)
This member attribute identifies the color of the media. Valid
values are 'red', 'white' and 'blue'
The "media-color-supported" (1setOf (type3 keyword | name(MAX)))
Printer attribute identifies the values of this "media-color"
member attribute that the Printer supports, i.e., the colors
supported.
If the client omits this member attribute, the Printer determines
the value in an implementation dependent manner.
5.1.2 media-size (collection)
This member attribute identifies the size of the media. The
'collection' consists of the member attributes shown in Table 2:
Table 2 - "media-size" collection member attributes
Attribute attribute syntax request Printer
name Support
x-dimension integer (0:MAX) MUST MUST
y-dimension integer (0:MAX) MUST MUST
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The definitions for the member attributes is given in the
following sub-sections:
5.1.2.1 x-dimension (integer(0:MAX))
This attribute identifies the width of the media in inch units
along the X axis.
5.1.2.2 y-dimension (integer(0:MAX))
This attribute identifies the height of the media in inch
units along the Y axis.
The "media-size-supported" (1setOf collection) Printer
attribute identifies the values of this "media-size" member
attribute that the Printer supports, i.e., the size
combinations supported. The names of the member attributes
are the same as the member attributes of the "media-size"
collection attribute, namely "x-dimension", and "y-dimension",
since they have the same attribute syntax and the same
semantics.
5.2 media-col-default (collection)
The "media-col-default" Printer attribute specifies the media that
the Printer uses, if any, if the client omits the "media-col" and
"media". Job Template attribute in the Job Creation operation (and
the PDL doesn't include a media specification). The member
attributes are defined in Table 1. A Printer MUST support the same
member attributes for this default collection attribute as it
supports for the corresponding "media-col" Job Template attribute.
5.3 media-col-ready (1setOf collection)
The "media-col-ready" Printer attribute identifies the media that are
available for use without human intervention, i.e., the media that
are ready to be used without human intervention. The collection
value MUST have all of the member attributes that are supported in
Table 1.
5.4 media-col-supported (1setOf type2 keyword)
The "media-col-supported" Printer attribute identifies the keyword
names of the member attributes supported in the "media-col"
collection Job Template attribute, i.e., the keyword names of the
member attributes in Table 1 that the Printer supports.
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6 A Second Example Definition Of A Collection Attribute
All of the example attribute definitions in this document are
illustrative examples, rather than actual definitions. These
examples are intended to illustrate how to define collection
attributes. Other documents MUST define collection attributes for
use in actual interchange. Such definitions may be very similar to
the examples in this document, since we attempted to pick useful
examples.
In some printing environments, it is desirable to allow the client to
select the media for the job start sheet. The reason for not adding
the 'collection' attribute syntax to the existing "job-sheets" Job
Template attribute is the same as for "media". Instead, a new Job
Template attribute is introduced, e.g. "job-sheet-col (collection)".
The member attributes of "job-sheet-col" attribute ("job-sheets
(type 3 keyword)" and "media (type3 keyword | name)") both follow
the naming rules of item 4a1 of section 3, i.e they reuse existing
IPP attributes. According to the rules, their supported values come
from the existing IPP attributes: "job-sheets-supported" and "media-
supported". However, their default values do not come from "job-
sheets-default" and "media-default", respectively. Rather the
definition of "job-sheet-col" says that "job-sheets (type 3 keyword)"
is required and if "media (type3 keyword | name)" is absent, the
Printer uses the same media as the rest of the job uses.
If "job-sheet-col" attribute were defined to contain the member
attribute "job-sheet-media (type3 keyword | name)" instead of "media
(type3 keyword | name)", then the definition would also have to
specify a "job-sheet-media-supported (1setOf (type3 keyword |
name))" whose values would be independent of "media-supported
(1setOf (type3 keyword | name))" and would be set separately by a
System Administrator.
The actual text for the definition of the attribute is left as an
exercise for the reader.
7 Encoding
This section defines the additional encoding tags used according to
[RFC2910] and gives an example of their use. The encoding tags
define in this document MUST be used by all collection attributes
defined in other documents. However, the example of their use is
illustrative only.
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7.1 Additional tags defined for representing a collection attribute
value
The 'collection' attribute syntax uses the tags defined in Table 3.
Table 3 - Tags defined for encoding the 'collection' attribute syntax
Tag name Tag Meaning
value
begCollection 0x34 Begin the collection attribute value.
endCollection 0x37 End the collection attribute value.
memberAttrName 0x4A The value is the name of the
collection member attribute
When encoding a collection attribute "xxx" that contains an attribute
"aaa" and is not inside another collection, the encoding follows
these rules:
1. The beginning of the collection is indicated with a value tag
that MUST be syntax type 'begCollection' (0x34) with a name
length and Name field that represent the name of the collection
attribute ("xxx") as with any attribute, followed by a value. The
Printer MAY ignore the value and its length of MAY be 0. In the
future, however, this field MAY contain useful information, such
as the collection name (cf. the name of a C struct).
2. Each member attribute is encoded as a sequence of two or more
values that appear to be part of a single multi-valued attribute,
i.e. 1setOf. The first value after the 'begCollection' value has
the attribute syntax 'memberAttrName' (0x4A) and its value holds
the name of the first member attribute (e.g. "aaa"). The second
value holds the first member's attribute value, which can be of
any attribute syntax, except 'memberAttrName' or 'endCollection'.
If the first member's attribute value is multi-valued, the third
value holds the second value of the first member's value.
Otherwise, the third value holds the name of second member
attribute (e.g. "bbb") and its attribute syntax is
'memberAttrName'. In this case, the fourth member's value is the
value of "bbb".
Note that the technique of encoding a 'collection' as a '1setOf'
makes it easy for a Printer that doesn't support a particular
deBry, et al. Expires: July 24, 2001 [page 16]
INTERNET-DRAFT IPP: The 'collection' attribute syntax Jan 24, 2001
collection attribute (or the collection attribute syntax at all)
to simply skip over the entire collection value.
3. The end of the collection is indicated with a value tag that MUST
be syntax type 'endCollection' (e.g. 0x37) and MAY have a zero
name length and a zero value length. In the future, this field
MAY contain useful information,such as the collection name that
matches the one in the 'begCollection' .
4. It is valid to have a member attribute that is, itself, a
collection attribute, i.e., collections can be nested within
collections. This is represented by the occurrence of a member
attribute that is of attribute syntax type 'begCollection'. Such
a collection is terminated by a matching 'endCollection'. The
name of such a member attribute is in the immediately preceding
value whose syntax type is 'memberAttrName'.
5. It is valid for a collection attribute to be multi-valued, i.e.,
have more than one collection value. If the next attribute
immediately following the 'endCollection' has a zero name length
and a tag of 'begCollection', then the collection attribute is a
multi-valued collection, as with any attribute. This statement
applies to collections within collections and collections that
are not in collections.
7.2 Example encoding: "media-col" (collection)
The collection specified in section 5 is used for the encoding
example shown in Table 5. The example also shows nested collections,
since the "media-size" member attribute is a 'collection. The
encoding example represents a blue 4x6-index cards and takes 216
octets. The Appendices contains more complex examples.
Additional examples have been included in the appendices.
The overall structure of the two collection values can be pictorially
represented as:
"media-col" =
{ "media-color" = 'blue';
"media-size" =
{ "x-dimension" = 6;
"y-dimension" = 4
}
},
The full encoding is in table 4. A simplified view of the encoding
looks like this:
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Table 4 - Overview Encoding of "media-col" collection
Tag Value Name Value
begCollection media-col ""
memberAttrName "" media-color
keyword "" blue
memberAttrName "" media-size
begCollection "" ""
memberAttrName "" x-dimension
integer "" 6
memberAttrName "" y-dimension
integer "" 4
endCollection "" ""
endCollection "" ""
Table 5 - Example Encoding of "media-col" collection
Octets Symbolic Value Protocol comments
field
0x34 begCollection value-tag beginning of the "media-
col" collection attribute
0x0009 name- length of (collection)
length attribute name
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Octets Symbolic Value Protocol comments
field
media-col media-col name name of (collection)
attribute
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
0x4A memberAttrName value-tag starts a new member
attribute: "media-color"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000B value- length of "media-color"
length keyword
media-color media-color value value is name of 1st
member attribute
0x44 keyword type value-tag keyword type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0004 value-
length
blue blue value value of 1st member
attribute
0x4A memberAttrName value-tag starts a new member
attribute: "media-size"
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Octets Symbolic Value Protocol comments
field
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000A value- length of "media-size"
length keyword
media-size media-size value Name of 2nd member
attribute
0x34 begCollection value-tag Beginning of the "media-
size" collection attribute
which is a sub-collection
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0000 value- collection attribute names
length have no value
no value (since value-
length was 0)
0x4A memberAttrName value-tag starts a new member
attribute: "x-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000B value- length of "x-dimension"
length keyword
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Octets Symbolic Value Protocol comments
field
x-dimension x-dimension value name of 1st sub-
collection member
attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0006 value value of 1st sub-
collection member
attribute
0x4A memberAttrName value-tag starts a new member
attribute: "y-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000B value- length of the "y-
length dimension" keyword
y-dimension y-dimension value name of 2nd sub-
collection member
attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
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Octets Symbolic Value Protocol comments
field
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0004 value value of 2nd sub-
collection member
attribute
0x37 endCollection value-tag end of the sub-collection
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
0x37 endCollection value-tag end of the 1st collection
value in 1setOf
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
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INTERNET-DRAFT IPP: The 'collection' attribute syntax Jan 24, 2001
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
and their values will look like a 1setOf values of the collection
attribute, so that the Printer simply ignores the entire attribute
and all of its values. Returning unsupported attributes is also
simple, since only the name of the collection attribute is returned
with the 'unsupported' out-of-band value (see section 4.2).
9 IANA Considerations
This section contains the exact information for IANA to add to the
IPP Registries according to the procedures defined in "IPP/1.1 Model
and Semantics" document [RFC2911] section 6.
Note to RFC Editors: Replace RFC NNNN below with the RFC number for
this document, so that it accurately reflects the content of the
information for the IANA Registry.
9.1 Attribute Syntax Registration
The attribute syntax defined in this document will be published by
IANA according to the procedures in RFC 2911 [RFC2911] section 6.3
with the following path:
ftp.isi.edu/iana/assignments/ipp/attribute-syntaxes/
The registry entry will contain the following information:
Reference:
RFC NNNN [this document]
Attribute Syntaxes: Ref. Section:
collection RFC NNNN 3
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
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INTERNET-DRAFT IPP: The 'collection' attribute syntax Jan 24, 2001
internationalization considerations, as may any attribute, according
to [RFC2911].
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 [RFC2911].
12 References
[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.
[RFC2565]
Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
Protocol/1.0: Encoding and Transport", RFC 2565, April 1999.
[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.
deBry, et al. Expires: July 24, 2001 [page 24]
INTERNET-DRAFT IPP: The 'collection' attribute syntax Jan 24, 2001
[RFC2910]
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.
[RFC2911]
Isaacson, S., deBry, R., Hastings, T., Herriot, R., Powell, P.,
"Internet Printing Protocol/1.1: Model and Semantics", RFC 2911,
September 2000.
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
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
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EMail: peter.zehler@usa.xerox.com
14 Appendix A: Encoding Example of a Simple Collection
The overall structure of the collection value can be pictorially
represented as:
" media-size " =
{ "x-dimension" = 6;
"y-dimension" = 4
}
A simplified view of the encoding would look like this:
Table 6 - Overview Encoding of simple collection
Tag Value Name Value
begCollection media-size ""
memberAttrName "" x-dimension
integer "" 6
memberAttrName "" y-dimension
integer "" 4
endCollection "" ""
Note: "" represents a name or value whose length is 0.
Table 7 - Example Encoding of simple collection
Octets Symbolic Value Protocol comments
field
0x34 begCollection value-tag beginning of the "media-
size" collection attribute
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Octets Symbolic Value Protocol comments
field
0x000A name- length of (collection)
length attribute name
media-size media-size name name of (collection)
attribute
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
0x4A memberAttrName value-tag starts member attribute:
"x-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000B value- length of "x-dimension"
length keyword
x-dimension x-dimension value name of 1st collection
member attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0006 value value of 1st collection
member attribute
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Octets Symbolic Value Protocol comments
field
0x4A memberAttrName value-tag starts a new member
attribute: "y-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000B value- length of the "y-
length dimension" keyword
y-dimension y-dimension value name of 2nd collection
member attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf for
length media-size
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0004 value value of 2nd collection
member attribute
0x37 endCollection value-tag end of the collection
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0000 value- defined to be 0 for this
length type
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Octets Symbolic Value Protocol comments
field
no value (since value-
length was 0)
15 Appendix B: Encoding Example of 1setOf Collection
The overall structure of the collection value can be pictorially
represented as:
"media-size-supported" =
{ "x-dimension" = 6;
"y-dimension" = 4
},
{ "x-dimension" = 3;
"y-dimension" = 5
};
A simplified view of the encoding would look like this:
Table 8 - Overview Encoding of 1setOf collection
Tag Value Name Value
begCollection media-size- ""
supported
memberAttrName "" x-dimension
integer "" 6
memberAttrName "" y-dimension
integer "" 4
endCollection "" ""
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INTERNET-DRAFT IPP: The 'collection' attribute syntax Jan 24, 2001
begCollection "" ""
memberAttrName "" x-dimension
integer "" 3
memberAttrName "" y-dimension
integer "" 5
endCollection "" ""
Table 9 - Example Encoding of 1setOf collection
Octets Symbolic Value Protocol comments
field
0x34 begCollection value-tag beginning of the "media-
size-supported (1setOf
collection" attribute
0x00014 name- length of (collection)
length attribute name
media-size- media-size- name name of (collection)
supported supported attribute
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
0x4A memberAttrName value-tag starts member attribute:
"x-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
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Octets Symbolic Value Protocol comments
field
0x000B value- length of "x-dimension"
length keyword
x-dimension x-dimension value name of 1st collection
member attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0006 value value of 1st collection
member attribute
0x4A memberAttrName value-tag starts member attribute:
"y-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000B value- length of the "y-
length dimension" keyword
y-dimension y-dimension value name of 2nd collection
member attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
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Octets Symbolic Value Protocol comments
field
0x0004 value- length of an integer = 4
length
0x0004 value value of 2nd collection
member attribute
0x37 endCollection value-tag end of the collection
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
0x34 begCollection value-tag beginning of the 2nd
member of the 1SetOf
"sizes-avail " collection
attribute
0x0000 name- Zero length name indicates
length this is member of previous
attribute
name no name (since name-length
was 0)
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
0x4A memberAttrName value-tag starts member attribute:
"x-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
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Octets Symbolic Value Protocol comments
field
no name (since name-length
was 0)
0x000B value- length of "x-dimension"
length keyword
x-dimension x-dimension value name of 1st collection
member attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0003 value value of 1st collection
member attribute
0x4A memberAttrName value-tag starts member attribute:
"y-dimension"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x000B value- length of the "y-
length dimension" keyword
y-dimension y-dimension value name of 2nd collection
member attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
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Octets Symbolic Value Protocol comments
field
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0005 value value of 2nd collection
member attribute
0x37 endCollection value-tag end of the 1setOf
collection value
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
16 Appendix C: Encoding Example of Collection containing 1setOf XXX
attribute
The overall structure of the collection value can be pictorially
represented as:
"wagons" =
{ "colors" = red, blue;
"sizes" = 4, 6, 8
}
A simplified view of the encoding would look like this:
Table 10 - Overview Encoding of collection with 1setOf value
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INTERNET-DRAFT IPP: The 'collection' attribute syntax Jan 24, 2001
Tag Value Name Value
begCollection wagons ""
memberAttrName "" colors
keyword "" red
keyword "" blue
memberAttrName "" sizes
integer "" 4
integer "" 6
integer "" 8
endCollection "" ""
Table 11 - Example Encoding of collection with 1setOf value
Octets Symbolic Value Protocol comments
field
0x34 begCollection value-tag beginning of the "wagons"
collection attribute
0x0005 name- length of (collection)
length attribute name
wagons wagons name name of (collection)
attribute
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
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Octets Symbolic Value Protocol comments
field
0x4A memberAttrName value-tag starts a new member
attribute: "colors"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0006 value- length of "colors" keyword
length
colors colosr value value is name of 1st
member attribute
0x44 keyword type value-tag keyword type
0x0000 name- 0 indicates 1setOf wagons
length
no name (since name-length
was 0)
0x0004 value-
length
blue blue value value of 1st member
attribute
0x44 keyword type value-tag keyword type
0x0000 name- 0 indicates 1setOf wagons
length
no name (since name-length
was 0)
0x0003 value-
length
red red value value of 1st member
attribute
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Octets Symbolic Value Protocol comments
field
0x4A memberAttrName value-tag starts a new member
attribute: "sizes"
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0005 value- length of "length-avail"
length keyword
sizes sizes value Name of 2nd member
attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf wagons
length
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0004 value 1st value for 1SetOf
integer attribute
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0006 value 2nd value for 1SetOf
integer attribute
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Octets Symbolic Value Protocol comments
field
0x21 integer type value-tag attribute type
0x0000 name- 0 indicates 1setOf
length
no name (since name-length
was 0)
0x0004 value- length of an integer = 4
length
0x0008 value 3rd value for 1SetOf
integer attribute
0x37 endCollection value-tag end of the collection
0x0000 name- defined to be 0 for this
length type, so part of 1setOf
no name (since name-length
was 0)
0x0000 value- defined to be 0 for this
length type
no value (since value-
length was 0)
17 Appendix D: Full Copyright Statement
Copyright (C) The Internet Society (1998,1999,2000,2001). 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
deBry, et al. Expires: July 24, 2001 [page 38]
INTERNET-DRAFT IPP: The 'collection' attribute syntax Jan 24, 2001
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.
deBry, et al. Expires: July 24, 2001 [page 39]
