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Latest DAV Version

From: Yaron Goland <yarong@microsoft.com>
Date: Sun, 10 Nov 1996 19:41:24 -0800
Message-ID: <c=US%a=_%p=msft%l=RED-44-MSG-961111034124Z-29389@INET-01-IMC.microsoft.com>
To: "'w3c-dist-auth@w3.org'" <w3c-dist-auth@w3.org>
This is the latest DAV spec. Jim and I are in the middle of a long
conversation about the relationships section. It currently reflects his
views. I would like to see some very major changes made to it but I felt
it was more important to get the spec out. Especially as it now contains
the versioning material. Jim will be posting the HTML version to the
website.
				Yaron
PS Does anyone have a good program for translating HTML into presentable
text?

WEBDAV Working Group                               Y. Goland, Microsoft
INTERNET-DRAFT                                     E. J. Whitehead, Jr.
                                                            U.C. Irvine

<draft-ietf-webdav-v1-spec-00>                         November 8, 1996

Expires April, 1997

Author's draft: v0.2
Extensions for Distributed Authoring and Versioning on the World Wide
Web 
Status of this Memo 
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups. Note that other groups may also distribute working
documents as Internet-Drafts. 
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or made obsolete by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress". 
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast). 
Distribution of this document is unlimited. Please send comments to the
WWW Distributed Authoring and Versioning (WEBDAV) working group at
<w3c-dist-auth@w3.org>, which may be joined by sending a message with
subject "subscribe" to <w3c-dist-auth-request@w3.org>. Discussions of
the WEBDAV working group are archived at
<URL:http://www.w3.org/pub/WWW/Archives/Public/w3c-dist-auth>. The HTTP
working group at <http-wg@cuckoo.hpl.hp.com> also discusses the HTTP
protocol. Discussions of the HTTP working group are archived at
<URL:http://www.ics.uci.edu/pub/ietf/http/>. General discussions about
HTTP and the applications which use HTTP should take place on the
<www-talk@w3.org> mailing list. 
Abstract 
TBD 
Changes Since Author Draft V0.1 
1. Added Undelete. 
2. Changed Notification section. 
3. Added versioning and access control sections. 
4. Added annotation, attributeset, search, and modifiable attributes. I
think attributeset is going to solve the problem with Larry. 
5. Rewrote and rearranged the attribute section. 
6. Changed the source attribute definition. 
7. Added attribute header, shared mode and principal to the terminology
section. 
8. Moved the definitions of copy, move, and redirect to the terminology
section. I also updated the terminology section to remove references to
representation. 
9. Added relationship to the terms section and wrote the relationship
section. 
10. Note that the Distributed Authoring commands assume that headers
will be used for representation negotiation while the Versioning
commands assume that only resources can be referred to and thus a
particular representation must be addressable using only a URL. Also
note that the versioning mime types contain both request and response
formats and that response formats identify themselves. This is not
strictly necessary with HTTP as one can tell if a message is a response
from context. However for maximum flexibility the mime times provide an
indication that it is a response so the mime times could be used with
e-mail or other mime delivery systems. 
11. Changed attribute URL syntax to allow attributes to have their own
attributes.
1. Introduction 
1.1 Purpose 
This specification defines extensions to the HTTP/1.1 [HTTP11] protocol,
the URL [URL] specification, and defines subtypes of the Application
content type [RFC1521]. Together, these provide a means for augmenting
existing facilities for remote authoring with abilities for locking,
versioning, relationships, attributes, and listing and manipulation of
the URL name space. Capabilities detailed in this specification meet the
requirements for Distributed Authoring and Versioning, stated in [ref DA
Reqt's][ref Vers. Reqt's]. 
1.2 Terminology 
Unless otherwise noted below, the use of terminology in this document is
consistent with the definitions of terms given in [HTTP11]. 
attribute header 
A header which returns information about the nature of a resource. 
attribute set 
An attribute set is a defined set of attribute headers. An attribute set
is used to indicate which attribute headers a resource provides support
for. This does not mean that the resource expresses all of the headers
in the set. Attribute sets MUST NOT be used as a substitute for unique
naming of attribute headers. 
check in 
A Check In is a declaration that the principal no longer intends to edit
a resource(s). 
check out 
A Check Out is a declaration by a principal that they intend to edit a
resource(s). 
command comments 
Command Comments associate either a string or a URI with an HTTP
message. 
copy 
A copy performs a byte-for-byte duplication of a resource, making it
available at both the original and new location in the URI namespace. 
destroy 
To destroy a resource is to request that the resource be permanently
removed from storage. This differs from delete in that some versioning
systems handle delete as a request to no longer make the specified
resource editable. 
diff 
A diff is a mechanism whereby two or more resources are compared and the
differences enumerated. 
history 
The history of a resource is a list of all the versions of the resource
along with related information. 
merge 
A merge is the process whereby information from multiple resources is
folded into a single resource. Merges can occur at the client or the
server. 
move 
A move is logically a copy followed by a delete of the source resource. 
no-modify lock 
A no-modify lock prevents a locked resource from being edited until all
no-modify locks are released. 
notify request 
A notify request instructs the recipient to send information regarding
the progress of a request. 
principal 
The source of a message; for example: persons, computers, and programs. 
read lock 
A read lock prevents principals who do not posses a read lock on a
resource from reading that resource. 
redirect 
Redirect is used to instruct a server to return one of the 3xx series
codes. 
relationship 
A relationship, or link, is a typed bi-directional attribute header
which provides a connection between two or more resources. 
representation 
"An entity included with a response that is subject to content
negotiation... There may exist multiple representations associated with
a particular response status." - [HTTP11] Each of these representations
is potentially subject to individual modification. 
shared mode 
Shared mode modifies a lock request such that the lock may be shared
between multiple requestors. 
write lock 
A write lock prevents anyone who does not possess a write lock on a
resource from editing that resource. 
1.3 Notational Conventions and Generic Grammar 
This specification uses the Augmented BNF and Basic Rules as defined in
Section 2 of [HTTP11]. 
1.4 Mime Format 
[This section doesn't really belong in the introduction.  Needs to be
moved.] 
Mime types sent with POSTs are used to transmit the commands specified
in this document. The request-URI, unless specified otherwise, points to
a resource that is capable of executing the request. 
In addition all the Mime types start the BNF element MIMEVersion which
is defined as: 
MIMEVersion = 1#DIGIT "." 1#DIGIT 
The semantics of MIMEVersion is the same as for HTTP-Version defined in
section 3.1 of [HTTP11]. 
2. Attributes 
During distributed authoring it is often necessary to record meta data
about a resource, such as a resource's creator, the date of its
completion, and the organization responsible for its maintenance. Once
created, these attributes can be used to precisely search resources, and
create a repository for organizational memory about the resource.
Attributes provide meta data capability by allowing named data elements
to be created, modified, read, and deleted on a resource.  An attribute
on a resource is a pair (name, value) consisting of the attribute's name
and value. 
The existing HTTP specification uses header fields to transmit meta
data.  This specification defines a new type of header field, known as
attribute header fields, which provide information about a resource's
nature, not its content or transmission state.  Attribute header fields
consist of a header name and an associated value, and are used to
provide attributes on resources. 
Rather then inventing a raft of new methods, the current methods will be
bent to our purposes. Below, a convention for placing the name of an
attribute within a URI is given.  This convention allows existing HTTP
methods to be invoked on attributes. So, for example, when a GET is
performed on an attribute header URI, the value of the attribute header
is returned in the entity-body.  Similarly, a PUT may be used to set the
value of an attribute on a resource. 
2.1 Attribute Header URIs 
A specification is provided below for describing an attribute header in
the context of the URI of the header's associated resource. So, were an
attribute header named "FileName" to exist and be associated with the
resource http://foo/bar, it would be uniquely referred to as
http://foo/bar<FileName>. Headers may also have a hierarchy so the URI
http://foo/bar<Author.FirstAuthor> would refer to the header
"FirstAuthor" which is a child of the header "Author." The "." is used
to denote hierarchy because it is legal to use within a token. Note that
the name space for headers is actually flat and the use of "." to denote
hierarchy is optional. It is only meant to make it easier to group
headers. The "<...>" enclosure was chosen because it will not cause a
conflict with any currently existing URIs. 
To support requests for attributes the definition of a URI must be
altered as follows: 
URI = ( absoluteURI | relativeURI ) *("<" Attribute ">") ["#" fragment]
Attribute = field-name ; See section 4.2 of [HTTP11] 
By convention an attribute request which ends in a "." and which does
not resolve to a specific attribute name SHOULD be treated as a request
for a list of all attributes in that hierarchy. 
In order to prevent name space collisions both headers and header
prefixes should be registered with a central authority. A header prefix
is any legal token that may only be used when it is prefixed to another
token. Prefixes should use the "." hierarchy format. Thus Netscape could
register the prefix NS and thus be the only organization allowed to
create headers which begin with "NS.". 
2.2 Interaction with Existing Methods and Proposed Functionality 
This section describes the precise semantics of existing HTTP methods
when applied to an attribute header of a resource. 
2.2.1 GET 
A GET of an attribute resource MUST return the value of the attribute in
the entity body of the response. Type of reponse - TBD 
Since attribute headers may grow to very large sizes and may contain
octet data, it is not feasible to include attribute headers in the
response to a GET on a resource. Therefore attribute headers SHOULD not
be transmitted as a response header. 
2.2.2 HEAD 
A HEAD method invocation on an attribute resource MUST behave as
specified in Section 9.4 (HEAD) of [HTTP11].  Attribute headers SHOULD
not be transmitted as a reponse header in the response to a HEAD
request. 
2.2.3 POST 
A POST may not be performed on an attribute header resource. 
2.2.4 PUT 
A PUT on an attribute resource MUST set the value of the attribute to
the contents of the entity body, following the semantics specified in
Section 9.6 (PUT) of [HTTP11]. 
2.2.5 DELETE 
A DELETE causes the attribute resource to be made unavailable. 
2.2.6 OPTIONS and TRACE 
These methods are unmodified from HTTP/1.1. 
2.2.7 Copy and Move 
When a resource is copied, moved, or otherwise manipulated, its
attributes are equally affected. However servers make the final
determination regarding the state of any attribute header and may choose
to not copy, move, etc. any subset of headers when it performs the
requested action on a resource. 
2.3 Standard Attributes 
The following attributes have their name and semantics defined by this
specification. 
[TBD - Currently only brief descriptions are included. Once we have
decided which ones should survive we will provide MIME types and other
information.] 
AttributeDirectory 
The attribute AttributeDirectory returns a list of all attribute headers
on a resource. To retrieve a list of attribute headers associated with
the URL http://foo/bar one would send a GET request with a request-URI
of /bar<AttributeDirectory>, where Host would equal foo. The same logic
applies to PUT, which would be used to set an attribute's value. 
AttributeSet 
This attribute returns a list of the attribute sets currently being used
to describe the resource. Support of an attribute set does not indicate
that all of its attributes are being used. For a list of all attributes
in use, the AttributeDirectory attribute should be retrieved. For
example, if some attributes from the Dublin Core were being used to
describe a resource, AttributeSet might contain the value "Dublin", or
"DC". The tag used to denote attributes defined in this specification is
"RFCxxxx". 
CheckedOut 
This attribute header returns a SiteMap containing a list of principals
who have checked out the resource. 
DirectoryName 
This attribute returns a name suitable for presentation in a directory.
The attribute embeds content headers to indicate language, character
set, etc. 
History 
See History, section 9.2. 
Link 
Contains information about resources that are related to this resource.
A SiteMap representation SHOULD be available.
[TBD: Review the SiteMap format and figure out tag formats to define
source links.] 
Link.Version 
This attribSee Version, Section 9.3. 
LockInformation 
See Lock Discovery, Section 3.2. 
Modifiable (this is a weak form of access control query) 
Indicates if the principal can modify the resource. 
NotifyRequest 
See Notify Request, Section 6. 
Relationships 
See Relationships, Section 5. 
Search 
The search attribute returns a URI that points to a resource which can
handle searching. It is currently expected that the URI returned will be
a HTTP URL which points to a search page. 
Source 
The URI of the resource as stored, without any processing by the server
(e.g. without processing of server-side includes). 
Version 
See Version, Section 9.3. 
3. Lock/Unlock 
Locks come in three types: write, read, and no-modify. Logically a write
lock and a read lock can co-exist on a single resource. This means that
one set of principals can edit the resource and another set of
principals are the only ones allowed to read it. This may seem "silly"
but is actually used in Orange book [ORANGE] compliant environments. A
write lock and a no-modify lock can not be used together for obvious
reasons. A read lock and a no-modify lock can be used together. 
Locks are assigned to a subset of the representations available for a
resource. If the lock only applies to a single representation then the
lock may be further restricted to only a particular range of the
representation. A content-range header is used for this purpose. The
range may go off the "end" of the representation. Locks that exceed the
end of a representation control the ability to append to the
representation. 
Locks may be taken out either in exclusive or shared mode. In shared
mode anyone with proper access may take out a lock. In exclusive mode
only the principal(s) who originally took out the lock may edit the
lock. However a new principal can be added to an exclusive lock if the
holder of the lock token performs the addition. 
If an entire resource is write locked and a lock owner deletes the
resource then the write lock remains. So long as the write lock remains
the URI can not be edited. 
In order to provide for maximum flexibility and ease of administration,
lock tokens will be used to track locks. When a lock is taken out a lock
token will be returned. A single lock token can represent any number of
locks. In future lock requests the same token may have new locks added
or old locks removed from it. Lock tokens are not required to be
transferable between lock administration resources. 
Locks also have time outs associated with them. If no time out value is
associated with a lock then the lock will never time out. Otherwise the
lock will expire if a number of seconds equal to the time out value
passes without the resource being accessed by a lock owner. The time out
value may be edited, without affecting the rest of the lock, by
submitting a lock request with no Lock Entries. 
Finally, locks may be taken out for multiple principals in a single
request. The Lock_Owners field allows for tokens to be used to identify
multiple principals who are considered owners of the lock. A server
SHOULD only allow a lock token to be used in a request if the requestor
is an owner of that lock token. 
[TBD - We need an error message indicating that the server will not
accept certain lock combinations or accept overlapping locks. We also
need an error stating that an unlock couldn't be executed because it did
not exactly match with a lock.] 
Locks will be implemented using POST. The request-URI will be the lock
administration resource. The entity-body will be of type
application/lock. 
3.1 Definition of Content Type application/lock 
LOCK_BODY = Token_Status Time_Out Lock_Owners Lock_Entries
Token_Status = (Token_Field | "No Token")
Token_Field = "Lock Token" ":" LockToken
Time_Out = "Time Out" ":" (*DIGIT | "Never")
Lock_Entries = "Lock Entries" ":" *(Lock_URI LockType (("Exclusive" |
"Shared") | "Unlock") Headers CRLF)
Lock_Owners = "Lock Owner" ":" #Lock_Owner
Lock_Owner = token; This is some identifier used to list who owns the
lock.
Lock_URI = "URI" ":" URI
LockToken = Any OCTET but LWS
LockType = ("Write" | "Read" | "No-Modify")
Headers = #message-header ; As defined in 4.2 of [1] 
Examples of type application/lock include: 
No Token
Time Out: Never
Lock Entries: URI http://www.microsoft.com/staff/yarong.html Write
Exclusive
[Yaron Goland <yarong@microsoft.com>] 
This specifies a request for an exclusive write lock on
http://www.microsoft.com/staff/yarong.html, held by Yarong Goland. This
lock will never automatically time out. 
3.2 Processing a Lock Request 
A lock request without a LockToken is a new lock request. All the
requests in a lock must be granted or a 503 Service Unavailable must be
returned. If the lock is granted then the return body should be formated
as: 
RETURN_LOCK_BODY = LockToken 
A lock request with a LockToken is a request to extend the lock
represented by the lock token. The same rules as specified in the
previous paragraph apply. 
A lock request with Unlock specified for Lock_Request means that all
locks associated with this token should be removed. 
A lock entries with Unlock specified means this particular lock should
be removed from the token. 
The BNF allows for Unlocks to be specified without specifying a lock
token. This is not an error. This syntax allows authorized principals to
override locks they do not have the token for. 
Lock requests MUST be processed as an atomic action or the request must
be refused. 
When multiple resources are locked under a single token an operation
will only be allowed on any of the resources if the remaining locks in
the token can be guaranteed to exist for the life of the operation. 
3.3 Lock Discovery 
When a lock is taken out the system SHOULD record who owns the lock.
Ownership information can be taken from the From header, from
identification provided by authentication, or from the LockOwners field.
This information SHOULD be available through the attribute header
"LockInformation" which has the mime type application/LockInformation.
The format of the mime entity-body is: 
LOCKINFORMATION = #(Token_Field Time_Out Lock_Owners Lock_Entries)
[Contact_Field]
Contact_Field = "Contact" ":" token 
The Contact_Field is used to provide contact information in case there
is a problem with a lock. 
An example of a LockInformation attribute is: 
LockInformation:
Token: a5dzq 
Time Out: Never 
[Yaron Goland <yarong@microsoft.com]
Lock Entries: URI http://www.microsoft.com/staff/yarong.html Write
Exclusive
Contact: Lock Administrator <lockadmin@microsoft.com> 
The exclusive write lock on http://www.microsoft.com/staff/yarong.html
is held by Yaron Goland, has token value a5dqz, and will never time out.
If there is a problem with a lock, the Lock Administrator should be
contacted. 
4. Name Space Manipulation 
4.1 Copy 
A copy performs a byte-for-byte duplication of a resource, making it
available at both the original and new location in the URI namespace.
There is no guarantee that the result of a GET on the URL of the
resource copy will be identical to a GET on the original resource. For
example, copying a script to a new location will often remove it from
its intended environment, and cause it to either not work, or produce
erroneous output. A copy MUST be atomic. 
A copy is performed by sending a POST method to a resource which can
perform the copy. The entity-body for the POST method is of content type
application/copy, defined in Section 4.1.1. 
Before any copied resources are made available through the destination
URIs, all copied resources must either be available or return a 503
Service Unavailable response code when referenced. 
If the No Overwrite value is specified then that entry in the copy
should not occur if the destination URI already exists. If a resource is
not copied because a "No Overwrite" flag was used and the resource
exists then the request still succeeds. 
4.1.1 Definition of Content Type application/copy 
BODY = 1*(Source_URI Headers Destination_URI Headers Type)
Source_URI = URI
Destination_URI = URI
Type = "Overwrite" | "No Overwrite"
Headers = #message-header ; As defined in 4.2 of [HTTP11] 
Examples of content type application/copy include: 
http://www.ics.uci.edu/~ejw/hidden/draft.html
Accept-Language: fr, en;q=0.7
http://www.ics.uci.edu/~ejw/final_report.html
Overwrite 
This example specifies a copy of the French language version of
http://www.ics.uci.edu/~ejw/hidden/draft.html if available, otherwise
any English version, into http://www.ics.uci.edu/~ejw/final_report.html,
overwriting the contents of final_report.html if they exist. 
http://www.ics.uci.edu/pub/ietf/http/index.html
Range: bytes=0-500
http://www.ics.uci.edu/~ejw/working.html
Range: bytes=0-500
Overwrite 
This example specifies a copy of the first 500 bytes of
/pub/ietf/index.html into /~ejw/working.html, overwriting the first 500
bytes of working.html if they exist. 
4.2 Destroy, Delete, and Undelete 
To destroy a resource is to request that the resource and its attribute
headers be permanently removed from storage. To delete a resource is to
request that the resource no longer be made available for editing.
Destory differs from delete in that a versioning system may allow a
deleted resource to be visible, but not editable, while a destroy causes
the resource, and all knowledge about the resource to be removed from
the server.  A destroy is performed by sending a POST message with an
entity-body of type application/delete, defined in Section 4.2.1. 
An undelete undoes the action of a delete, making a deleted resource
available for editing.  An undelete is performed by sending a POST
message with  entity-body of content type application/delete, with a
listing of the resources to be undeleted. 
4.2.1 Definition of Content Type application/delete 
Application/Delete = Request | Response
Request = "Request" 1#(URI ("Delete" | "Destroy" | "Undelete"))
Response = "Response" 1#(URI ("Delete" | "Destroy" | "Undelete")
("Success" | "Failure") (comment | Status-Line) 
Note that this definition allows for the specification of a mix of
delete and destroy operations. A "Delete" entry should be treated the
same as if a Delete method were sent to the specified URI (as defined in
Section 9.7 of [HTTP11]). 
An example of content type application/delete is: 
Request 
http://www.ics.uci.edu/~ejw/hidden/draft.html Delete
http://www.ics.uci.edu/~ejw/hidden/draft.png Destroy 
This specifies a request to make the resource
http://www.ics.uci.edu/~ejw/hidden/draft.html unavailable, but not
necessarily deleted from the server, and to completely destroy resource
http://www.ics.uci.edu/~ejw/hidden/draft.png, erasing it from the
underlying storage mechanism.  A possible reponse to this request would
be the following reponse entity-body: 
Response
http://www.ics.uci.edu/~ejw/hidden/draft.html Delete Success
http://www.ics.uci.edu/~ejw/hidden/draft.png Destroy Failure 403
Forbidden 
4.3 Move 
A move is logically a copy followed by a delete of the source resource.
A move MUST be atomic. A move is performed by sending a POST method to a
resource which can perform the move. The entity-body of the POST method
is of content type application/move, defined exactly the same as content
type application/copy, (Section 4.1.1). 
In this case atomicity requires that before the resources are made
available at the new location they must no longer be available at the
old location. The rest of the atomicity requirements are the same as for
copy. 
4.4 Redirect 
Redirect is used to instruct a server to redirect all further requests
on a resource, or set of resources. A redirection can be used to
instruct the server to return one of the following response codes: 301
Moved Permanently, 302 Moved Temporarily, 303 See Other, or 305 Use
Proxy. A Redirect request specifies both the reponse code and the URL to
which it applies. 
To perform a redirect a POST should be performed with the content-type
equal to application/redirect, defined in section 4.4.1. 
4.4.1 Definition of Content Type application/redirect 
The body of the mime type is defined as TBD. [The mime type will contain
the URL being redirected, the code to be used, and the semantics of the
entity-body to be returned.] 
5. Relationships 
[NOTE: The authors are currently in the middle of a very long and
detailed conversation about this section. This section reflects Jim's
views on how relationships should be specified. My views are radically
different. I want to see relationships specified as attributes in the
attribute name space using the normal attribute control mechanisms. I
believe documents will have many relationships and it will not be
feasible to drag these around in the header. This was the same reasoning
that lead to the creation of attributes and why I want relationships to
be attributes.]
A relationship specifies how two or more resources are related. Examples
of relationships include "author-of," "table of contents," and
"specifies." A relationship can exist within a resource, and between
mutliple resources.  These resources may be of any media type, and a
relationship can exist between resources of differing media type. When
considering relationships which exist between resources, due to the
distribution of resources across the Web, it is often the case that the
relationship spans multiple servers.  As a result, instead of being
stored once, between resources, the endpoints of a relationship must be
stored on individual resources.  For the purposes of this specification,
a relationship is defined to be a set of relationship endpoints. To
create a multiway (or n-ary) relationship, a client must individually
create each endpoint of the relationship, specifying at each endpoint
which other relationship endpoints (usually on other resources) are part
of the relationship. 
A hypertext link is a relationship which a client has made available to
the user interface so a user can jump to the other endpoints of the
relationship using the hypertext point-click-and-traverse user interface
style.  A link is always a relationship, but a relationship is not
always a hypertext link. 
To request the creation of a relationship endpoint, a POST message with
entity body of content-type application/relationship should be issued to
the administration resource for relationships. 
5.1 Definition of Content Type application/relationship 
REL/BODY = Relationship-request | Relationship-response
Relationship-request = 1*( Rel-action Rel-token Rel-spec )
Relationship-response = 1*( Rel-action Rel-token Rel-spec Rel-response )
Rel-spec = Rel-URI Link  ; Link is defined in Section 19.6.2.4 of
[HTTP11]
Rel-URI = "URI" ":" URI
Rel-action = "Add" | "Remove" | "Modify"
Rel-token = *1("RToken" ":" rtoken)   ; Specifying token for an Add
request is optional
Rel-status = Status-Code SP Reason-Phrase   ; As defined in [HTTP11]
rtoken = token 
The ability to specify relationship endpoints on resources of any
content type is mostly provided by the Link entity header field defined
in 19.6.2.4 of [HTTP11]. The Link entity header field is used in this
specification, with minor additions which add the ability to specify
that another endpoint belongs to this relationship.  This cabability is
provided by an additional link-param field, called peer. The contents of
a peer field are a sequence of (URI, relationship token) tuples, which
list the opposite endpoints of the relationship. The relationship token
MUST uniquely identify a relationship endpoint on a particular resource,
but does not have to be globally unique across all resources. 
( "peer" "=" 1# "(" <"> URI <"> "," rtoken ")" )

An example of content type application/relationship is: 
Add
URI: http://www.ics.uci.edu/authoring/meeting/intro.html
RToken: 1
Link: <http://www.ics.uci.edu/authoring/meeting/agenda.html>;
rel="Child";
peer=("http://www.ics.uci.edu/authoring/meeting/agenda.html, 2) 
Add 
URI: http://www.ics.uci.edu/authoring/meeting/agenda.html
RToken: 2
Link: <http://www.ics.uci.edu/authoring/meeting/intro.html>;
rel="Parent";
peer=("http://www.ics.uci.edu/authoring/meeting/intro.html", 1) 
This defines a binary parent-child relationship between intro.html and
agenda.html. From this example, it may seem that having the URI in the
peer field is redundant. For binary relationships, this is indeed the
case. However, the URI is required for multiway relationships, where
more than one peer link needs to be specified in a peer parameter. 
6. Notification 
6.1 Notify Request Header 
The Notify Request request-header is used to request that the server
send a stream of "102 Process" messages containing updates of the
request's status. 
Notify_Request = "NotifyRequest" ":" 
6.2 Resource Event Notification 
As features such as WebCheck and URLMinder demonstrate, there is a
strong interest in receiving notification when a resource changes. What
is lacking is a standard means to register interest in receiving
notification regarding a resource. 
6.2.1 Definition of Content Type application/ResourceNotification 
The following specification proposes the mime type
application/RequestNotification which is used to set the attribute
RequestNotification. This solves the problem by providing a standardized
method to register interest and to specify how one wishes to receive
information. 
Application/ResourceNotification = 1#(On_Resource Notification_Means
On_Event)
On_Resource = URI
Notification_Means = URI
On_Event = #token 
On_Resource specifies the resource for which notification is being
requested. Notification_Means species a URI which will indicate how to
notify the requester. On_Event specifies what event must occur in order
for the notification to be sent. If no On_Event is specified then the
server chooses when to notify the requester. 
Possible On_Event values include "Deleted", "Accessed", "Faxed",
"Printed", "Mailed", "AttributesModified", and "LockLost" ":" LockToken.
6.2.2 Definition of Content Type application/NotificationData 
The actual notification is protocol dependent. However, the content type
application/NotificationData is defined as follows: 
Application/NotificationData = 1#(On_Resource On_Event) 
7. URI Container 
Any resource which has a representation of content type
application/container, is defined to be a URI container. Content type
application/container will use the SiteMap format. 
The advantage of SiteMaps in this context is that they are designed to
point to other SiteMaps. In this way a hierarchy can be built and when
an operation is performed it will act recursively down the tree. 
[TBD - Do we really want to teach every DAV system to do HTML? Perhaps
we want to introduce another access mechanism?] 
8. Versioning Mime Types 
8.1 Check In/Out 
A Check In is a declaration that the principal no longer intends to edit
a resource(s).  A Check Out is a declaration by a principal that they
intend to edit a resource(s).  An RCS-style locking check out is
performed by issuing a request for a write lock, immediately followed by
a request which requests a check-out (as specified below).  A CVS-style
non-locking checkout is performed by only issuing a request for a
check-out. 
8.1.1 Definition of Content Type application/checkinout 
Application/CheckInOut = CheckInOutRequest | CheckInOutResponse 
CheckInOutRequest = ["Atomic"] "Request" 1#Requests 
Requests = URI ("CheckIn" | "CheckOut" ("Exclusive" | "Shared")) 
CheckInOutResponse = "Response" 1#Responses
Responses = URI ("CheckIn" | "CheckOut" ("Exclusive" | "Shared"))Status 
Status = ("Success" | "Failure") comment 
If a request contains "Atomic" then all the elements in the request must
be granted or rejected. 
The "Exclusive" and "Shared" keywords indicate if a check out is
exclusive or shared on the specified resource. 
[TBD - We can always get rid of the versioning header by overloading
Check In and making it a versioning PUT. Though we still need a
"UnCheckOut" which is a CheckIn with no body.] 
8.2 Diff/Merge 
The purpose of the Diff or Merge is to take all the specified URIs and
entities and return a single Diff or a single Merge of the results. Many
servers will not be able to handle more than two resources and will
return an error if more are specified. 
8.2.1 Definition of Content Type application/DiffMerge 
Application/Diff = Body
Application/Merge = Body
Body = 1#("URI" ":" URI | "Entity" ":" entity-body) 
9. Versioning Headers 
9.1 Command Comments 
Command comments are entity headers. 
Command_Comment = "Comment" ":" CommentVal
CommentVal = URI | comment 
This is the standard comment facility used by versioning systems.
Servers that do not understand the header or do not wish to make use of
the information are free to ignore the information. No specification is
made regarding how this information is to be retrieved. It is likely,
however, that most systems will make the command comments available
through their history attribute. 
9.2 History 
History is an attribute header that returns a SiteMap containing the
history of the document. 
9.3 Version 
The version entity header is used with PUT to create a new version or to
begin versioning an entity. 
Version = "version" ":" token 
When included with a PUT on a new resource it indicates that the
resource should be versioned and what version token should be used. The
server is not required to accept the version token. The actual version
token used along with the URI the resource will be accessible from must
be returned in the response body. 
When included with a PUT on the URI of a currently existing versioned
resource the version entity header indicates that the entity is a new
version of that resource. The server will indicate what the URI of the
new version of the resource is along with its version token in the
response. 
If the version entity header is included with other methods then the
header should be interpreted as a request for a particular version of
the resource. However this interpretation is non-standard as one version
is semantically different than another and the header thus may be
dropped. 
In addition to the version entity header there also exists a version
link attribute header. TBD. 
Acknowledgements 
Roy Fielding, Richard Taylor, Larry Masinter, Henry Sanders, Judith
Slein, Dan Connolly, David Durand, Henrik Nielsen. Others, TBD. 
References 
[HTTP11] R. T. Fielding, J. Gettys, J. C. Mogul, H. F. Nielsen, and T.
Berners-Lee. "Hypertext Transfer Protocol -- HTTP/1.1" Internet-Draft
draft-ietf-http-v11-spec-07.txt, expires February 12, 1997. 
[ORANGE] DoD 5200.28-STD, "Department of Defense Trusted Computer System
Evaluation Criteria", December, 1985. 
[RFC1521] N. Borenstein, N. Freed. "MIME (Multipurpose Internet Mail
Extensions) Part One: Mechanisms for Specifying and Describing the
Format of Internet Message Bodies." RFC 1521, Bellcore, Innsoft,
September, 1993. 
[URL] T. Berners-Lee, L. Masinter, M. McCahill. "Uniform Resource
Locators (URL)." RFC 1738, CERN, Xerox PARC, University of Minnesota,
December, 1994. 
Received on Sunday, 10 November 1996 22:41:20 GMT

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