Network Working Group J. Whitehead

Network Working Group J. Whitehead
Request for Comments: 3648 U.C. Santa Cruz
Category: Standards Track J. Reschke, Ed.
greenbytes
December 2003

Web Distributed Authoring and Versioning (WebDAV)
Ordered Collections Protocol

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

This specification extends the Web Distributed Authoring and
Versioning (WebDAV) Protocol to support the server-side ordering of
collection members. Of particular interest are orderings that are
not based on property values, and so cannot be achieved using a
search protocol's ordering option and cannot be maintained
automatically by the server. Protocol elements are defined to let
clients specify the position in the ordering of each collection
member, as well as the semantics governing the ordering.

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Table of Contents

1. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview of Ordered Collections . . . . . . . . . . . . . . . 5
4.1. Additional Collection properties . . . . . . . . . . . . 6
4.1.1. DAV:ordering-type (protected). . . . . . . . . . 6
5. Creating an Ordered Collection . . . . . . . . . . . . . . . . 7
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Example: Creating an Ordered Collection. . . . . . . . . 8
6. Setting the Position of a Collection Member. . . . . . . . . . 8
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Examples: Setting the Position of a Collection Member. . 10
6.3. Examples: Renaming a member of an ordered collection . . 10
7. Changing a Collection Ordering: ORDERPATCH method. . . . . . . 11
7.1. Example: Changing a Collection Ordering. . . . . . . . . 13
7.2. Example: Failure of an ORDERPATCH Request. . . . . . . . 14
8. Listing the Members of an Ordered Collection . . . . . . . . . 16
8.1. Example: PROPFIND on an Ordered Collection . . . . . . . 17
9. Relationship to versioned collections. . . . . . . . . . . . . 19
9.1. Collection Version Properties. . . . . . . . . . . . . . 20
9.1.1. Additional semantics for
DAV:version-controlled-binding-set (protected) . 20
9.1.2. DAV:ordering-type (protected). . . . . . . . . . 20
9.2. Additional CHECKIN semantics . . . . . . . . . . . . . . 20
9.3. Additional CHECKOUT Semantics. . . . . . . . . . . . . . 20
9.4. Additional UNCHECKOUT, UPDATE, and MERGE Semantics . . . 21
10. Capability Discovery . . . . . . . . . . . . . . . . . . . . . 21
10.1. Example: Using OPTIONS for the Discovery of Support for
Ordering . . . . . . . . . . . . . . . . . . . . . . . . 22
10.2. Example: Using Live Properties for the Discovery of
Ordering . . . . . . . . . . . . . . . . . . . . . . . . 22
11. Security Considerations. . . . . . . . . . . . . . . . . . . . 23
11.1. Denial of Service and DAV:ordering-type . . . . . . . . 23
12. Internationalization Considerations. . . . . . . . . . . . . . 24
13. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 24
14. Intellectual Property Statement. . . . . . . . . . . . . . . . 25
15. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
17. Normative References . . . . . . . . . . . . . . . . . . . . . 26
A. Extensions to the WebDAV Document Type Definition. . . . . . . 27
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 30

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1. Notational Conventions

Since this document describes a set of extensions to the WebDAV
Distributed Authoring Protocol [RFC2518], which is itself an
extension to the HTTP/1.1 protocol, the augmented BNF used here to
describe protocol elements is exactly the same as described in
Section 2.1 of HTTP [RFC2616]. Since this augmented BNF uses the
basic production rules provided in Section 2.2 of HTTP, these rules
apply to this document as well.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

This document uses XML DTD fragments as a purely notational
convention. WebDAV request and response bodies can not be validated
due to the specific extensibility rules defined in section 23 of
[RFC2518] and due to the fact that all XML elements defined by this
specification use the XML namespace name "DAV:". In particular:

1. element names use the "DAV:" namespace,

2. element ordering is irrelevant,

3. extension elements (elements not already defined as valid child
elements) may be added anywhere, except where explicitly stated
otherwise,

4. extension attributes (attributes not already defined as valid for
this element) may be added anywhere, except where explicitly
stated otherwise.

2. Introduction

This specification builds on the collection infrastructure provided
by the WebDAV Distributed Authoring Protocol, adding support for the
server-side ordering of collection members.

There are many scenarios in which it is useful to impose an ordering
on a collection at the server, such as expressing a recommended
access order, or a revision history order. The members of a
collection might represent the pages of a book, which need to be
presented in order if they are to make sense, or an instructor might
create a collection of course readings that she wants to be displayed
in the order they are to be read.

Orderings may be based on property values, but this is not always the
case. The resources in the collection may not have properties that

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can be used to support the desired ordering. Orderings based on
properties can be obtained using a search protocol's ordering option,
but orderings not based on properties cannot. These orderings
generally need to be maintained by a human user.

The ordering protocol defined here focuses on support for such
human-maintained orderings. Its protocol elements allow clients to
specify the position of each collection member in the collection's
ordering, as well as the semantics governing the order. The protocol
is designed to allow additional support in the future for orderings
that are maintained automatically by the server.

The remainder of this document is structured as follows: Section 3
defines terminology that will be used throughout the specification.
Section 4 provides an overview of ordered collections. Section 5
describes how to create an ordered collection, and Section 6
discusses how to set a member's position in the ordering of a
collection. Section 7 explains how to change a collection ordering.
Section 8 discusses listing the members of an ordered collection.
Section 9 discusses the impact on version-controlled collections (as
defined in [RFC3253]). Section 10 describes capability discovery.
Sections 11 through 13 discuss security, internationalization, and
IANA considerations. The remaining sections provide supporting
information.

3. Terminology

The terminology used here follows that in [RFC2518] and [RFC3253].
Definitions of the terms resource, Uniform Resource Identifier (URI),
and Uniform Resource Locator (URL) are provided in [RFC2396].

Ordered Collection

A collection for which the results from a PROPFIND request are
guaranteed to be in the order specified for that collection.

Unordered Collection

A collection for which the client cannot depend on the
repeatability of the ordering of results from a PROPFIND request.

Client-Maintained Ordering

An ordering of collection members that is maintained on the server
based on client requests specifying the position of each
collection member in the ordering.

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Server-Maintained Ordering

An ordering of collection members that is maintained automatically
by the server, based on a client's choice of ordering semantics.

Ordering Semantics

In general, ordering semantics are the set of structures or
meanings applied to the ordering of the member of a specific
collection. Within this document, "ordering semantics" refers
specifically to the structure specified in the DAV:ordering-type
property. See Section 4.1.1 for more information on
DAV:ordering-type.

This document uses the terms "precondition", "postcondition" and
"protected property" as defined in [RFC3253]. Servers MUST report
pre-/postcondition failures as described in section 1.6 of this
document.

4. Overview of Ordered Collections

If a collection is not ordered, the client cannot depend on the
repeatability of the ordering of results from a PROPFIND request. By
specifying an ordering for a collection, a client requires the server
to follow that ordering whenever it responds to a PROPFIND request on
that collection.

Server-side orderings may be client-maintained or server-maintained.
For client-maintained orderings, a client must specify the ordering
position of each of the collection's members, either when the member
is added to the collection (using the Position header (Section 6)) or
later (using the ORDERPATCH (Section 7) method). For server-
maintained orderings, the server automatically positions each of the
collection's members according to the ordering semantics. This
specification supports only client-maintained orderings, but is
designed to allow the future extension with server-maintained
orderings.

A collection that supports ordering is not required to be ordered.

If a collection is ordered, each of its internal member URIs MUST
appear in the ordering exactly once, and the ordering MUST NOT
include any URIs that are not internal members of the collection.
The server is responsible for enforcing these constraints on
orderings. The server MUST remove an internal member URI from the
ordering when it is removed from the collection. Removing an
internal member MUST NOT affect the ordering of the remaining

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internal members. The server MUST add an internal member URI to the
ordering when it is added to the collection.

Only one ordering can be attached to any collection. Multiple
orderings of the same resources can be achieved by creating multiple
collections referencing those resources, and attaching a different
ordering to each collection.

An ordering is considered to be part of the state of a collection
resource. Consequently, the ordering is the same no matter which URI
is used to access the collection and is protected by locks or access
control constraints on the collection.

4.1. Additional Collection properties

A DAV:allprop PROPFIND request SHOULD NOT return any of the
properties defined in this document.

4.1.1. DAV:ordering-type (protected)

The DAV:ordering-type property indicates whether the collection is
ordered and, if so, uniquely identifies the semantics of the
ordering. It may also point to an explanation of the semantics in
human and/or machine-readable form. At a minimum, this allows human
users who add members to the collection to understand where to
position them in the ordering. This property cannot be set using
PROPPATCH. Its value can only be set by including the Ordering-Type
header with a MKCOL request or by submitting an ORDERPATCH request.

Ordering types are identified by URIs that uniquely identify the
semantics of the collection's ordering. The following two URIs are
predefined:

DAV:custom: The value DAV:custom indicates that the collection is
ordered, but the semantics governing the ordering are not being
advertised.

DAV:unordered: The value DAV:unordered indicates that the collection
is not ordered. That is, the client cannot depend on the
repeatability of the ordering of results from a PROPFIND request.

An ordering-aware client interacting with an ordering-unaware server
(e.g., one that is implemented only according to [RFC2518]) SHOULD
assume that the collection is unordered if a collection does not have
the DAV:ordering-type property.

<!ELEMENT ordering-type (href) >

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5. Creating an Ordered Collection

5.1. Overview

When a collection is created, the client MAY request that it be
ordered and specify the semantics of the ordering by using the new
Ordering-Type header (defined below) with a MKCOL request.

For collections that are ordered, the client SHOULD identify the
semantics of the ordering with a URI in the Ordering-Type header,
although the client MAY simply set the header value to DAV:custom to
indicate that the collection is ordered but the semantics of the
ordering are not being advertised. Setting the value to a URI that
identifies the ordering semantics provides the information a human
user or software package needs to insert new collection members into
the ordering intelligently. Although the URI in the Ordering-Type
header MAY point to a resource that contains a definition of the
semantics of the ordering, clients SHOULD NOT access that resource to
avoid overburdening its server. A value of DAV:unordered in the
Ordering-Type header indicates that the client wants the collection
to be unordered. If the Ordering-Type header is not present, the
collection will be unordered.

Additional Marshalling:

Ordering-Type = "Ordering-Type" ":" absoluteURI
; absoluteURI: see RFC2396, section 3

The URI "DAV:unordered" indicates that the collection is not
ordered, while "DAV:custom" indicates that the collection is to be
ordered, but the semantics of the ordering is not being
advertised. Any other URI value indicates that the collection is
ordered, and identifies the semantics of the ordering.

Additional Preconditions:

(DAV:ordered-collections-supported): the server MUST support
ordered collections in the part of the URL namespace identified by
the request URL.

Additional Postconditions:

(DAV:ordering-type-set): if the Ordering-Type header was present,
the request MUST have created a new collection resource with the
DAV:ordering-type being set according to the Ordering-Type request
header. The collection MUST be ordered unless the ordering type
is "DAV:unordered".

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5.2. Example: Creating an Ordered Collection

>> Request:

MKCOL /theNorth/ HTTP/1.1
Host: example.org
Ordering-Type: http://example.org/orderings/compass.html

>> Response:

HTTP/1.1 201 Created

In this example, a new ordered collection was created. Its
DAV:ordering-type property has the URI from the Ordering-Type header
as its value http://example.org/orderings/compass.html. In this
case, the URI identifies the semantics governing a client-maintained
ordering. As new members are added to the collection, clients or end
users can use the semantics to determine where to position the new
members in the ordering.

6. Setting the Position of a Collection Member

6.1. Overview

When a new member is added to a collection with a client-maintained
ordering (for example, with PUT, COPY, or MKCOL), its position in the
ordering can be set with the new Position header. The Position
header allows the client to specify that an internal member URI
should be first in the collection's ordering, last in the
collection's ordering, immediately before some other internal member
URI in the collection's ordering, or immediately after some other
internal member URI in the collection's ordering.

If the Position request header is not used when adding a member to an
ordered collection, then:

o If the request is replacing an existing resource, the server MUST
preserve the present ordering.

o If the request is adding a new internal member URI to the
collection, the server MUST append the new member to the end of
the ordering.

Note to implementers: this specification does not mandate a specific
implementation of MOVE operations within the same parent collection.
Therefore, servers may either implement this as a simple rename
operation (preserving the collection member's position), or as a
sequence of "remove" and "add" (causing the semantics of "adding a

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new member" to apply). Future revisions of this specification may
specify this behaviour more precisely based on future implementation
experience.

Additional Marshalling:

Position = "Position" ":" ("first" | "last" |
(("before" | "after") segment))

segment is defined in Section 3.3 of [RFC2396].

The segment is interpreted relative to the collection to which the
new member is being added.

When the Position header is present, the server MUST insert the
new member into the ordering at the specified location.

The "first" keyword indicates that the new member is placed in the
beginning position in the collection's ordering, while "last"
indicates that the new member is placed in the final position in
the collection's ordering. The "before" keyword indicates that
the new member is added to the collection's ordering immediately
prior to the position of the member identified in the segment.
Likewise, the "after" keyword indicates that the new member is
added to the collection's ordering immediately following the
position of the member identified in the segment.

If the request is replacing an existing resource and the Position
header is present, the server MUST remove the internal member URI
from its current position, and insert it at the newly requested
position.

Additional Preconditions:

(DAV:collection-must-be-ordered): the target collection MUST be
ordered.

(DAV:segment-must-identify-member): the referenced segment MUST
identify a resource that exists and is different from the affected
resource.

Additional Postconditions:

(DAV:position-set): if a Position header is present, the request
MUST create the new collection member at the specified position.

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6.2. Examples: Setting the Position of a Collection Member

>> Request:

COPY /~user/dav/spec08.html HTTP/1.1
Host: example.org
Destination: http://example.org/~slein/dav/spec08.html
Position: after requirements.html

>> Response:

HTTP/1.1 201 Created

This request resulted in the creation of a new resource at
example.org/~slein/dav/spec08.html. The Position header in this
example caused the server to set its position in the ordering of the
/~slein/dav/ collection immediately after requirements.html.

>> Request:

MOVE /i-d/draft-webdav-prot-08.txt HTTP/1.1
Host: example.org
Destination: http://example.org/~user/dav/draft-webdav-prot-08.txt
Position: first

>> Response:

HTTP/1.1 409 Conflict
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx

<?xml version="1.0" encoding="utf-8" ?>
<D:error xmlns:D="DAV:">
<D:collection-must-be-ordered/>
</D:error>

In this case, the server returned a 409 (Conflict) status code
because the /~user/dav/ collection is an unordered collection.
Consequently, the server was unable to satisfy the Position header.

6.3. Examples: Renaming a member of an ordered collection

The following sequence of requests will rename a collection member
while preserving its position, independently of how the server
implements the MOVE operation:

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1. PROPFIND collection with depth 1, retrieving the DAV:ordering-type
property (an interactive client has already likely done this in
order to display the collection's content).

2. If the DAV:ordering-type property is present and does not equal
"dav:unordered" (thus if the collection is ordered), determine the
current position (such as "first" or "after x") and setup the
Position header accordingly.

3. Perform the MOVE operation, optionally supplying the Position
header computed in the previous step.

7. Changing a Collection Ordering: ORDERPATCH method

The ORDERPATCH method is used to change the ordering semantics of a
collection, to change the order of the collection's members in the
ordering, or both.

The server MUST apply the changes in the order they appear in the
order XML element. The server MUST either apply all the changes or
apply none of them. If any error occurs during processing, all
executed changes MUST be undone and a proper error result returned.

If an ORDERPATCH request changes the ordering semantics, but does not
completely specify the order of the collection members, the server
MUST assign a position in the ordering to each collection member for
which a position was not specified. These server-assigned positions
MUST follow the last position specified by the client. The result is
that all members for which the client specified a position are at the
beginning of the ordering, followed by any members for which the
server assigned positions. Note that the ordering of the server-
assigned positions is not defined by this document, therefore servers
can use whatever rule seems reasonable (for instance, alphabetically
or by creation date).

If an ORDERPATCH request does not change the ordering semantics, any
member positions not specified in the request MUST remain unchanged.

A request to reposition a collection member to the same place in the
ordering is not an error.

If an ORDERPATCH request fails, the server state preceding the
request MUST be restored.

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Additional Marshalling:

The request body MUST be DAV:orderpatch element.

<!ELEMENT orderpatch (ordering-type?, order-member*) >

<!ELEMENT order-member (segment, position) >
<!ELEMENT position (first | last | before | after)>
<!ELEMENT segment (#PCDATA)>
<!ELEMENT first EMPTY >
<!ELEMENT last EMPTY >
<!ELEMENT before segment >
<!ELEMENT after segment >

PCDATA value: segment, as defined in section 3.3 of [RFC2396].

The DAV:ordering-type property is modified according to the
DAV:ordering-type element.

The ordering of internal member URIs in the collection identified
by the Request-URI is changed based on instructions in the order-
member XML elements. Specifically, in the order that they appear
in the request. The order-member XML elements identify the
internal member URIs whose positions are to be changed, and
describe their new positions in the ordering. Each new position
can be specified as first in the ordering, last in the ordering,
immediately before some other internal member URI, or immediately
after some other internal member URI.

If a response body for a successful request is included, it MUST
be a DAV:orderpatch-response XML element. Note that this document
does not define any elements for the ORDERPATCH response body, but
the DAV:orderpatch-response element is defined to ensure
interoperability between future extensions that do define elements
for the ORDERPATCH response body.

<!ELEMENT orderpatch-response ANY>

Since multiple changes can be requested in a single ORDERPATCH
request, the server MUST return a 207 (Multi-Status) response
(defined in [RFC2518]), containing DAV:response elements for
either the request-URI (when the DAV:ordering-type could not be
modified) or URIs of collection members to be repositioned (when
an individual positioning request expressed as DAV:order-member
could not be fulfilled) if any problems are encountered.

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Preconditions:

(DAV:collection-must-be-ordered): see Section 6.1.

(DAV:segment-must-identify-member): see Section 6.1.

Postconditions:

(DAV:ordering-type-set): if the request body contained a
DAV:ordering-type element, the request MUST have set the
DAV:ordering-type property of the collection to the value
specified in the request.

(DAV:ordering-modified): if the request body contained DAV:order-
member elements, the request MUST have set the ordering of
internal member URIs in the collection identified by the request-
URI based upon the instructions in the DAV:order-member elements.

7.1. Example: Changing a Collection Ordering

Consider an ordered collection /coll-1, with bindings ordered as
follows:

three.html
four.html
one.html
two.html

>> Request:

ORDERPATCH /coll-1/ HTTP/1.1
Host: example.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" ?>
<d:orderpatch xmlns:d="DAV:">
<d:ordering-type>
<d:href>http://example.org/inorder.ord</d:href>
</d:ordering-type>
<d:order-member>
<d:segment>two.html</d:segment>
<d:position><d:first/></d:position>
</d:order-member>
<d:order-member>
<d:segment>one.html</d:segment>
<d:position><d:first/></d:position>
</d:order-member>

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<d:order-member>
<d:segment>three.html</d:segment>
<d:position><d:last/></d:position>
</d:order-member>
<d:order-member>
<d:segment>four.html</d:segment>
<d:position><d:last/></d:position>
</d:order-member>
</d:orderpatch>

>> Response:

HTTP/1.1 200 OK

In this example, after the request has been processed, the
collection's ordering semantics are identified by the URI http://
example.org/inorder.ord. The value of the collection's
DAV:ordering-type property has been set to this URI. The request
also contains instructions for changing the positions of the
collection's internal member URIs in the ordering to comply with the
new ordering semantics. As the DAV:order-member elements are
required to be processed in the order they appear in the request,
two.html is moved to the beginning of the ordering, and then one.html
is moved to the beginning of the ordering. Then three.html is moved
to the end of the ordering, and finally four.html is moved to the end
of the ordering. After the request has been processed, the
collection's ordering is as follows:

one.html
two.html
three.html
four.html

7.2. Example: Failure of an ORDERPATCH Request

Consider a collection /coll-1/ with members ordered as follows:

nunavut.map
nunavut.img
baffin.map
baffin.desc
baffin.img
iqaluit.map
nunavut.desc
iqaluit.img
iqaluit.desc

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>> Request:

ORDERPATCH /coll-1/ HTTP/1.1
Host: www.nunanet.com
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" ?>
<d:orderpatch xmlns:d="DAV:">
<d:order-member>
<d:segment>nunavut.desc</d:segment>
<d:position>
<d:after>
<d:segment>nunavut.map</d:segment>
</d:after>
</d:position>
</d:order-member>
<d:order-member>
<d:segment>iqaluit.map</d:segment>
<d:position>
<d:after>
<d:segment>pangnirtung.img</d:segment>
</d:after>
</d:position>
</d:order-member>
</d:orderpatch>

>> Response:

HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" ?>
<d:multistatus xmlns:d="DAV:">
<d:response>
<d:href>http://www.nunanet.com/coll-1/iqaluit.map</d:href>
<d:status>HTTP/1.1 403 Forbidden</d:status>
<d:responsedescription>
<d:error><d:segment-must-identify-member/></d:error>
pangnirtung.img is not a collection member.
</d:responsedescription>
</d:response>
</d:multistatus>

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In this example, the client attempted to position iqaluit.map after a
URI that is not an internal member of the collection /coll-1/. The
server responded to this client error with a 403 (Forbidden) status
code, indicating the failed precondition DAV:segment-must-identify-
member. Because ORDERPATCH is an atomic method, the request to
reposition nunavut.desc (which would otherwise have succeeded) failed
as well, but does not need to be expressed in the multistatus
response body.

8. Listing the Members of an Ordered Collection

A PROPFIND request is used to retrieve a listing of the members of an
ordered collection, just as it is used to retrieve a listing of the
members of an unordered collection.

However, when responding to a PROPFIND on an ordered collection, the
server MUST order the response elements according to the ordering
defined on the collection. If a collection is unordered, the client
cannot depend on the repeatability of the ordering of results from a
PROPFIND request.

In a response to a PROPFIND with Depth: infinity, members of
different collections may be interleaved. That is, the server is not
required to do a breadth-first traversal. The only requirement is
that the members of any ordered collection appear in the order
defined for that collection. Thus, for the hierarchy illustrated in
the following figure, where collection A is an ordered collection
with the ordering B C D,

A
/|\
/ | \
B C D
/ /|\
E F G H

it would be acceptable for the server to return response elements in
the order A B E C F G H D or "A B E C H G F D" as well (if C is
unordered). In this response, B, C, and D appear in the correct
order, separated by members of other collections. Clients can use a
series of Depth: 1 PROPFIND requests to avoid the complexity of
processing Depth: infinity responses based on depth-first traversals.

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

8.1. Example: PROPFIND on an Ordered Collection

Suppose a PROPFIND request is submitted to /MyColl/, which has its
members ordered as follows.

/MyColl/
lakehazen.html
siorapaluk.html
iqaluit.html
newyork.html

>> Request:

PROPFIND /MyColl/ HTTP/1.1

Host: example.org
Depth: 1
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx

<?xml version="1.0" ?>
<D:propfind xmlns:D="DAV:">
<D:prop xmlns:J="http://example.org/jsprops/">
<D:ordering-type/>
<D:resourcetype/>
<J:latitude/>
</D:prop>
</D:propfind>

>> Response:

HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx

<?xml version="1.0" ?>
<D:multistatus xmlns:D="DAV:"
xmlns:J="http://example.org/jsprops/">
<D:response>
<D:href>http://example.org/MyColl/</D:href>
<D:propstat>
<D:prop>
<D:ordering-type>
<D:href>DAV:custom</D:href>
</D:ordering-type>
<D:resourcetype><D:collection/></D:resourcetype>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

</D:propstat>
<D:propstat>
<D:prop>
<J:latitude/>
</D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>http://example.org/MyColl/lakehazen.html</D:href>
<D:propstat>
<D:prop>
<D:resourcetype/>
<J:latitude>82N</J:latitude>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop>
<D:ordering-type/>
</D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href
>http://example.org/MyColl/siorapaluk.html</D:href>
<D:propstat>
<D:prop>
<D:resourcetype/>
<J:latitude>78N</J:latitude>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop>
<D:ordering-type/>
</D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>http://example.org/MyColl/iqaluit.html</D:href>
<D:propstat>
<D:prop>
<D:resourcetype/>
<J:latitude>62N</J:latitude>
</D:prop>

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

<D:status>HTTP/1.1 200 OK</D:status>
</D:propstat>
<D:propstat>
<D:prop>
<D:ordering-type/>
</D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:response>
<D:response>
<D:href>http://example.org/MyColl/newyork.html</D:href>
<D:propstat>
<D:prop>
<D:resourcetype/>
<J:latitude>45N</J:latitude>
</D:prop>
<D:status>HTTP/1.1 200 OK</D:status>
<D:propstat>
<D:prop>
<D:ordering-type/>
</D:prop>
<D:status>HTTP/1.1 404 Not Found</D:status>
</D:propstat>
</D:propstat>
</D:response>
</D:multistatus>

In this example, the server responded with a list of the collection
members in the order defined for the collection.

9. Relationship to versioned collections

The Versioning Extensions to WebDAV [RFC3253] introduce the concept
of versioned collections, recording both the dead properties and the
set of internal version-controlled bindings. This section defines
how this feature interacts with ordered collections.

This specification considers both the ordering type (DAV:ordering-
type property) and the ordering of collection members to be part of
the state of a collection. Therefore, both MUST be recorded upon
CHECKIN or VERSION-CONTROL, and both MUST be restored upon CHECKOUT,
UNCHECKOUT or UPDATE (where for compatibility with RFC 3253, only the
ordering of version-controlled members needs to be maintained).

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

9.1. Collection Version Properties

9.1.1. Additional semantics for DAV:version-controlled-binding-set
(protected)

For ordered collections, the DAV:version-controlled-binding elements
MUST appear in the ordering defined for the checked-in ordered
collection.

9.1.2. DAV:ordering-type (protected)

The DAV:ordering-type property records the DAV:ordering-type property
of the checked-in ordered collection.

9.2. Additional CHECKIN semantics

Additional Postconditions:

(DAV:initialize-version-controlled-bindings-ordered): If the
request-URL identified a both ordered and version-controlled
collection, then the child elements of DAV:version-controlled-
binding-set of the new collection version MUST appear in the
ordering defined for that collection.

(DAV:initialize-collection-version-ordering-type): If the
request-URL identified a both ordered and version-controlled
collection, then the DAV:ordering-type property of the new
collection version MUST be a copy of the collection's
DAV:ordering-type property.

9.3. Additional CHECKOUT Semantics

Additional Postconditions:

(DAV:initialize-version-history-bindings-ordered): If the request
has been applied to a collection version with a DAV:ordering-type
other than "DAV:unordered", the bindings in the new working
collection MUST be ordered according to the collection version's
DAV:version-controlled-binding-set property.

(DAV:initialize-ordering-type): If the request has been applied to
a collection version, the DAV:ordering-type property of the new
working collection MUST be initialized from the collection
version's DAV:ordering-type property.

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

9.4. Additional UNCHECKOUT, UPDATE, and MERGE Semantics

Additional Postconditions:

(DAV:update-version-controlled-collection-members-ordered): If the
request modified the DAV:checked-in version of a version-
controlled collection and the DAV:ordering-type for the checked-in
version is not unordered ("DAV:unordered"), the version-controlled
members MUST be ordered according to the checked-in version's
DAV:version-controlled-binding-set property. The ordering of
non-version-controlled members is server-defined.

(DAV:update-version-ordering-type): If the request modified the
DAV:checked-in version of a version-controlled collection, the
DAV:ordering-type property MUST be updated from the checked-in
version's property.

10. Capability Discovery

Sections 9.1 and 15 of [RFC2518] describe the use of compliance
classes with the DAV header in responses to OPTIONS, indicating which
parts of the Web Distributed Authoring protocols the resource
supports. This specification defines an OPTIONAL extension to
[RFC2518]. It defines a new compliance class, called ordered-
collections, for use with the DAV header in responses to OPTIONS
requests. If a collection resource does support ordering, its
response to an OPTIONS request may indicate that it does, by listing
the new ORDERPATCH method as one it supports, and by listing the new
ordered-collections compliance class in the DAV header.

When responding to an OPTIONS request, only a collection or a null
resource can include ordered-collections in the value of the DAV
header. By including ordered-collections, the resource indicates
that its internal member URIs can be ordered. It implies nothing
about whether any collections identified by its internal member URIs
can be ordered.

Furthermore, RFC 3253 [RFC3253] introduces the live properties
DAV:supported-method-set (section 3.1.3) and DAV:supported-live-
property-set (section 3.1.4). Servers MUST support these properties
as defined in RFC 3253.

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

10.1. Example: Using OPTIONS for the Discovery of Support for
Ordering

>> Request:

OPTIONS /somecollection/ HTTP/1.1
Host: example.org

>> Response:

HTTP/1.1 200 OK
Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, ORDERPATCH
DAV: 1, 2, ordered-collections

The DAV header in the response indicates that the resource
/somecollection/ is level 1 and level 2 compliant, as defined in
[RFC2518]. In addition, /somecollection/ supports ordering. The
Allow header indicates that ORDERPATCH requests can be submitted to
/somecollection/.

10.2. Example: Using Live Properties for the Discovery of Ordering

>> Request:
PROPFIND /somecollection HTTP/1.1
Depth: 0
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" encoding="UTF-8" ?>
<propfind xmlns="DAV:">
<prop>
<supported-live-property-set/>
<supported-method-set/>
</prop>
</propfind>

>> Response:
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx

<?xml version="1.0" encoding="utf-8" ?>
<multistatus xmlns="DAV:">
<response>
<href>http://example.org/somecollection</href>
<propstat>
<prop>

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

<supported-live-property-set>
<supported-live-property>
<prop><ordering-type/></prop>
</supported-live-property>

</supported-live-property-set>
<supported-method-set>
<supported-method name="COPY" />
<supported-method name="DELETE" />
<supported-method name="GET" />
<supported-method name="HEAD" />
<supported-method name="LOCK" />
<supported-method name="MKCOL" />
<supported-method name="MOVE" />
<supported-method name="OPTIONS" />
<supported-method name="ORDERPATCH" />
<supported-method name="POST" />
<supported-method name="PROPFIND" />
<supported-method name="PROPPATCH" />
<supported-method name="PUT" />
<supported-method name="TRACE" />
<supported-method name="UNLOCK" />
</supported-method-set>
</prop>
<status>HTTP/1.1 200 OK</status>
</propstat>
</response>
</multistatus>

Note that actual responses MUST contain a complete list of supported
live properties.

11. Security Considerations

This section is provided to make WebDAV implementers aware of the
security implications of this protocol.

All of the security considerations of HTTP/1.1 and the WebDAV
Distributed Authoring Protocol specification also apply to this
protocol specification. In addition, ordered collections introduce a
new security concern. This issue is detailed here.

11.1. Denial of Service and DAV:ordering-type

There may be some risk of denial of service at sites that are
advertised in the DAV:ordering-type property of collections.
However, it is anticipated that widely-deployed applications will use
hard-coded values for frequently-used ordering semantics rather than

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

looking up the semantics at the location specified by DAV:ordering-
type. This risk will be further reduced if clients observe the
recommendation of Section 5.1 that requests not be sent to the URI in
DAV:ordering-type.

12. Internationalization Considerations

This specification follows the practices of [RFC2518] by encoding all
human-readable content using [XML] and in the treatment of names.
Consequently, this specification complies with the IETF Character Set
Policy [RFC2277].

WebDAV applications MUST support the character set tagging, character
set encoding, and the language tagging functionality of the XML
specification. This constraint ensures that the human-readable
content of this specification complies with [RFC2277].

As in [RFC2518], names in this specification fall into three
categories: names of protocol elements such as methods and headers,
names of XML elements, and names of properties. The naming of
protocol elements follows the precedent of HTTP using English names
encoded in USASCII for methods and headers. The names of XML
elements used in this specification are English names encoded in
UTF-8.

For error reporting, [RFC2518] follows the convention of HTTP/1.1
status codes, including with each status code a short, English
description of the code (e.g., 423 Locked). Internationalized
applications will ignore this message, and display an appropriate
message in the user's language and character set.

This specification introduces no new strings that are displayed to
users as part of normal, error-free operation of the protocol.

For the rationale of these decisions and advice for application
implementers, see [RFC2518].

13. IANA Considerations

This document uses the namespaces defined by [RFC2518] for properties
and XML elements. All other IANA considerations mentioned in
[RFC2518] also apply to this document.

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

14. Intellectual Property Statement

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.

15. Contributors

This document has benefited from significant contributions from Geoff
Clemm, Jason Crawford, Jim Davis, Chuck Fay and Judith Slein.

16. Acknowledgements

This document has benefited from thoughtful discussion by Jim Amsden,
Steve Carter, Tyson Chihaya, Ken Coar, Ellis Cohen, Bruce Cragun,
Spencer Dawkins, Mark Day, Rajiv Dulepet, David Durand, Lisa
Dusseault, Roy Fielding, Yaron Goland, Fred Hitt, Alex Hopmann,
Marcus Jager, Chris Kaler, Manoj Kasichainula, Rohit Khare, Daniel
LaLiberte, Steve Martin, Larry Masinter, Jeff McAffer, Surendra
Koduru Reddy, Max Rible, Sam Ruby, Bradley Sergeant, Nick Shelness,
John Stracke, John Tigue, John Turner, Kevin Wiggen, and others.

Whitehead & Reschke Standards Track [Page 25]

RFC 3648 WebDAV Ordered Collections Protocol December 2003

17. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.

[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.

[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, February 1999.

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

[RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C. and J.
Whitehead, "Versioning Extensions to WebDAV (Web
Distributed Authoring and Versioning)", RFC 3253, March
2002.

[XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-
xml, October 2000, <http://www.w3.org/TR/2000/REC-xml-
20001006>.

Whitehead & Reschke Standards Track [Page 26]

RFC 3648 WebDAV Ordered Collections Protocol December 2003

Appendix A. Extensions to the WebDAV Document Type Definition

<!ELEMENT orderpatch (ordering-type?, order-member*) >
<!ELEMENT order-member (segment, position) >
<!ELEMENT ordering-type (href) >
<!ELEMENT position (first | last | before | after)>
<!ELEMENT first EMPTY >
<!ELEMENT last EMPTY >
<!ELEMENT before segment >
<!ELEMENT after segment >
<!ELEMENT segment (#PCDATA)>

Index

C
Client-Maintained Ordering 4
Condition Names
DAV:collection-must-be-ordered (pre) 9
DAV:initialize-collection-version-ordering-type (post) 20
DAV:initialize-ordering-type (post) 21
DAV:initialize-version-controlled-bindings-ordered (post) 20
DAV:initialize-version-history-bindings-ordered (post) 20
DAV:ordered-collections-supported (pre) 7
DAV:ordering-modified (post) 13
DAV:ordering-type-set (post) 7, 13
DAV:position-set (post) 9
DAV:segment-must-identify-member (pre) 9
DAV:update-version-controlled-collection-members-ordered
(post) 21
DAV:update-version-ordering-type (post) 21

D
DAV header
compliance class 'ordered-collections' 21
DAV:collection-must-be-ordered precondition 9
DAV:custom ordering type 6
DAV:initialize-collection-version-ordering-type postcondition 20
DAV:initialize-ordering-type postcondition 21
DAV:initialize-version-controlled-bindings-ordered
postcondition 20
DAV:initialize-version-history-bindings-ordered postcondition 20
DAV:ordered-collections-supported precondition 7
DAV:ordering-modified postcondition 13
DAV:ordering-type property 6
DAV:ordering-type-set postcondition 7, 13
DAV:position-set postcondition 9
DAV:segment-must-identify-member precondition 9
DAV:unordered ordering type 6

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

DAV:update-version-controlled-collection-members-ordered
postcondition 21
DAV:update-version-ordering-type postcondition 21

H
Headers
Ordering-Type 7
Position 9

M
Methods
ORDERPATCH 11

O
Ordered Collection 4
Ordering Semantics 5
Ordering-Type header 7
ORDERPATCH method 11

P
Position header 9
Properties
DAV:ordering-type 6

S
Server-Maintained Ordering 5

U
Unordered Collection 4

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RFC 3648 WebDAV Ordered Collections Protocol December 2003

Authors' Addresses

Jim Whitehead
UC Santa Cruz, Dept. of Computer Science
1156 High Street
Santa Cruz, CA 95064
US

EMail: [email protected]

Julian F. Reschke, Ed.
greenbytes GmbH
Salzmannstrasse 152
Muenster, NW 48159
Germany

Phone: +49 251 2807760
Fax: +49 251 2807761
EMail: [email protected]
URI: http://greenbytes.de/tech/webdav/

Whitehead & Reschke Standards Track [Page 29]

RFC 3648 WebDAV Ordered Collections Protocol December 2003

Full Copyright Statement

Copyright (C) The Internet Society (2003). 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 assignees.

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

Acknowledgement

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

Whitehead & Reschke Standards Track [Page 30]