Subject: Re: Using PROPPATCH to create a resource with no body

From: [email-masked]
Date: Mon, 16 Aug 1999 16:45:47 -0400

I am generally in favor of using PROPPATCH to create and initialize the
properties of a resource. This would allow PROPPATCH to have the same semantics
as PUT. I am a little less comfortable with the overwrite header semantics. It
seems that overwrite is somewhat redundant with the propertyupdate element in
the body of the PROPPATCH request. Perhaps the semantics being handled by the
overwrite header could be included in the propertyupdate element. This would
allow more flexibility by indicating for each property how it should be handled,
and would not introduce a third state for overwrite which is currently a boolean
header.

There are a number of proposed extensions to PROPPATCH which I will summarize
here. Jim Whitehead, what needs to be done to get these extensions considered by
the WebDAV working group?

1. Allow PROPPATCH on a null resource to create a resource and initialize its
properties.

The spec is currently quiet about PROPPATCH on a null resource (a resource that
does not exist). It does say that PROPPATCH on a lock null resource (a resource
created by the LOCK method) will fail, but this is inconsistent with PUT which
is allowed, and changes the state of the resource from lock null to resource.

2. Extend the DAV:set and DAV:remove elements to include information describing
how the client wishes to handle errors. The DTD additions would be:

<!ELEMENT propertyupdate (remove | set)+>

<ELEMENT set (prop, updatebehavior?)>
<ELEMENT remove (prop, updatebehavior?)>

<!ELEMENT updatebehavior (ignore | mustsucceed)>
<!ELEMENT ignore EMPTY>
<!ELEMENT mustsucceed (#PCDATA | href+)>

If an updatebehavior is not included, it is equivalent to specifying
<mustsucceed>*</mustsucceed> meaning that all the updates must be successful or
none of them are performed. If a list of URIs is included as the value of
mustsucceed, then the named properties must be updated successfully. The #PCDATA
in element mustsucceed can only be "*" indicating all updates must be
successful. If ignore is specified, then the server must use best effort to
update the properties returning a multistatus indicating which properties were
not updated.

Currently, the spec says that all property updates must be successful, or none
are applied. In many instances, this is too restrictive requiring clients to
submit PROPPATCH requests, examine the multistatus returned to figure out which
updates failed, and re-submit a new PROPPATCH with the failures removed. This
situation arrises when different servers support different live properties. The
above extension to PROPPATCH allows client applications to have more control on
setting properties.

3. Add an add element to propertyupdate to distinguish between setting an
existing property and adding a new property.

Currently, propertyupdate includes set and remove. A client can either set the
value of an existing property, or add a new property with the set element. There
are some cases where the client does not want to set an element that already
exists, but there is currently no way to distinguish these operations in the
propertyupdate element. The extension provides an add element that would add a
new property to the resource. The add update would fail if the property already
has a value. This extension will be more important if we add extension 1 because
there will be many cases where a property should not be updated after it has
been set. For example, resourcetype, creationdate, etc.

"Geoffrey M. Clemm" <[email-masked]> on 08/16/99 01:53:54 PM

To:   [email-masked], [email-masked]
cc:

Subject:  Using PROPPATCH to create a resource with no body

The DeltaV versioning extensions to WebDAV propose four new
types of resources: workspace, activity, configuration, and history.

All these new resource types share the characteristic that their
state is represented as a set of properties, rather than in a body.
In this way, they are like the collection resource type from the
core WebDAV protocol, and the redirect-reference resource type from
the advanced collection WebDAV extensions.

A common issue for each of these new resource types is how one creates
an instance.  The approach started by the core WebDAV spec is
to introduce a new method for creating each new resource type
(e.g. MKCOL). This becomes rather burdensome when
the list starts growing (MKWORKSPACE, MKACTIVITY, MKCONFIGURATION,
MKHISTORY, ...), and is rather redundant since they all take the
form of initializing a set of properties of a new resource.

An alternative approach is to just allow PROPPATCH to create a new
resource when it is applied to a null resource.  I would propose
also adding a new value for the Overwrite header, e.g. Update,
which would say that the destination of operation should be updated,
rather than deleted (Overwrite=T) or have the operation fail (Overwrite=F).
Then the Overwrite header could be used to control the effect of a
PROPPATCH.

This is very consistent with the functionality of PUT, which can be
used either to update an existing resource or create a new resource.

Another alternative is to introduce a MKRESOURCE method, which would
be equivalent to a PROPATCH with Overwrite=F.

I personally favor extending PROPPATCH since it is both more consistent
with PUT, and a more powerful/flexible approach.  As a note, MKCOL would
then just become an alias for a PROPATCH, with the resourcetype
property set to be <D:collection/>

Comments?

Cheers,
Geoff

---

From: Jim Whitehead <[email-masked]>
Date: Mon, 16 Aug 1999 15:19:03 -0700

Jim Amsden writes:
> There are a number of proposed extensions to PROPPATCH which I
> will summarize here. Jim Whitehead, what needs to be done to get these
> extensions considered by the WebDAV working group?

Write them up in an Internet-Draft. This draft can then be used by the
document editors when RFC 2518 goes to Draft Standard.

> 1. Allow PROPPATCH on a null resource to create a resource and
> initialize its properties.
>
> The spec is currently quiet about PROPPATCH on a null resource (a
> resource that does not exist). It does say that PROPPATCH on a lock null
> resource (a resource created by the LOCK method) will fail, but this is
inconsistent
> with PUT which is allowed, and changes the state of the resource from lock
null
> to resource.

The intent of RFC 2518 was that PROPPATCH, like every other method that does
not create a resource, would return a 404 (Not Found) error.  The spec. does
not explicitly mention this, since we intended for all standard HTTP/1.1
error cases to be applied to WebDAV.  A PROPPATCH on a null resource is a
standard 404 (Not Found) error case, and hence we didn't think it needed
special mention.

- Jim