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Re: Informal Last Call: CalDAV Scheduling Extensions to WebDAV [Fwd: I-D Action:draft-desruisseaux-caldav-sched-07.txt]

From: Julian Reschke <julian.reschke@gmx.de>
Date: Mon, 13 Jul 2009 13:45:58 +0200
Message-ID: <4A5B1E76.7020803@gmx.de>
To: Bernard Desruisseaux <bernard.desruisseaux@oracle.com>
CC: caldav@ietf.org, calsify@ietf.org, w3c-dist-auth@w3.org, Cyrus Daboo <cyrus@daboo.name>, Alexey Melnikov <alexey.melnikov@isode.com>, Lisa Dusseault <Lisa.Dusseault@messagingarchitects.com>
Bernard Desruisseaux wrote:
> Cyrus and I submitted draft-desruisseaux-caldav-sched-07 to the IETF 
> last week.  See Internet-Draft announcement below.
> Before requesting the IESG to consider this Internet-Draft as a Proposed 
> Standard, we would like to get as much feedback as possible from the 
> participants of the "caldav" mailing list as well as from the members of 
> the WebDAV and Calsify Working Groups.
> Please review the document and send your comments to the caldav@ietf.org 
> mailing list by July 7th, 2009.
> We would like to submit draft -08 before July 13, 2009, i.e., the final 
> submission cut-off for the 75th IETF in Stockholm, Sweden.
> ...

Hi Bernard,

I'm sorry that I'm late with my feedback (attached below). Most are nits 
of editorial nature. Also, I have only read the spec from an HTTP/WebDAV 
point of view, as I'm no expert on calendaring at all.

There is a single non-editorial issue I found, and that is the 
introduction of the scheduling tag, with associated HTTP headers. I 
think it would be good to discuss this in more detail.

BR, Julian

--- snip ---
1.5.  XML Namespaces and Processing

    Definitions of XML elements in this document use XML element type
    declarations (as found in XML Document Type Declarations), described
    in Section 3.2 of [W3C.REC-xml-20081126].

JR: should this be a section reference?

    The XML declarations used in this document do not include namespace
    information.  Thus, implementers must not use these declarations as
    the only way to create valid CalDAV properties or to validate CalDAV
    XML element type.  Some of the declarations refer to XML elements

JR: I realize this sentence is borrowed from 4791. Does anybody recall what
the "...create valid CalDAV properties..." refers to? What does the DTD have
to do with that?

4.1.  Scheduling Outbox Collection

    While there is currently no defined use for child resources in a
    scheduling Outbox collection, a scheduling Outbox collection MAY
    contain child resources.

JR: may say "...MAY contain child resources, whose semantics are 
undefined for now..."?
...if this is correct, is it planned to add semantics later? How?

4.2.  Scheduling Inbox Collection

    Scheduling Inbox collections MUST only contain calendar object
    resources that obey the restrictions specified in iTIP
    [I-D.ietf-calsify-2446bis].  Consequently, scheduling Inbox
    collections MUST NOT contain any types of collection resources.
    Restrictions defined in Section 4.1 of CalDAV "calendar-access"
    [RFC4791] on calendar object resources contained in calendar
    collections (e.g., "UID" uniqueness) don't apply to calendar object
    resources contained in a scheduling Inbox collection.  Multiple
    calendar object resources contained in a scheduling Inbox collection
    MAY have the same "UID" property value (i.e., multiple scheduling
    messages for the same calendar component).

JR: last sentence just seems to rephrase the previous one. So maybe say 
"Thus, ..."
and remove the RFC2119 keyword.

5.1.  Identifying Scheduling Object Resources

    Calendar object resources on which the server performs automatic
    scheduling transactons are refered to as scheduling object resources.

JR: spelling.  Create

    The attempt to deliver the scheduling message will either succeed or
    fail.  In all cases, the server MUST add a "SCHEDULE-STATUS"
    iCalendar property parameter (see Section 10.3) to the "ATTENDEE"
    iCalendar property in the scheduling object resource being created,
    and set its value as described in Section 9.2.  This will result in
    the created calendar object resource differing from the calendar data
    sent in the HTTP request.  As a result clients MAY reload the
    calendar data from the server as soon as it is created on the server
    in order to update to the new server generated state information.

The "MAY" doesn't seem to be right here. This is not an interop requirement
but simply a statement of fact. They "MAY" reload whenever they want
anyway :-) (there are more occurrences of this language later on).

7.2.7.  CALDAV:max-resource-size Precondition

    Name:  max-resource-size

    Namespace:  urn:ietf:params:xml:ns:caldav

    Apply to:  POST

    Use with:  403 Forbidden

    Purpose:  (precondition) -- The resource submitted in the POST
       request MUST have an octet size less than or equal to the value of

JR: "octet size"? I thought that's 8 :-) Maybe "size in octets"?

8.  Conditional Requests on Scheduling Object Resources

    In order to do that, this specification introduces a new WebDAV
    resource property CALDAV:schedule-tag with a corresponding response
    header "Schedule-Tag", and a new "If-Schedule-Tag-Match" request
    header to allow client changes to be appropriately merged with server
    changes in the case where the changes on the server were the result
    of an "inconsequential" scheduling message update.  An
    "inconsequential" scheduling message is one which simply updates the
    status information of Attendees due to a reply from an Attendee.

JR: that sounds really heavy-weight; I think it would be good to discuss
this scenario over on the HTTPbis working group's mailing list. Even if new
state tokens need to be added it is not totally clear why the RFC4918
can not be used for checking.

11.1.  Schedule-Reply Request Header

       Schedule-Reply = "Schedule-Reply" ":" ("T" | "F")


       Schedule-Reply: F

    When an Attendee executes an HTTP DELETE request on a scheduling
    object resource, and the Schedule-Reply header is not present, or
    present and set to the value "T", the server MUST send an appropriate
    reply scheduling message with the Attendee's "PARTSTAT" iCalendar
    property parameter value set to "DECLINED" as part of its normal
    automatic scheduling transaction processing.

JR: is this header really really needed? Would it be possible to pass
that information in the request body instead?
Received on Monday, 13 July 2009 11:46:45 UTC

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