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Re: Proposal: WebDAV and transactions

From: Stefan Eissing <stefan.eissing@greenbytes.de>
Date: Fri, 13 Sep 2002 09:36:59 +0200
Cc: w3c-dist-auth@w3.org
Message-Id: <9627E886-C6EB-11D6-9F78-00039384827E@greenbytes.de>
To: "Clemm, Geoff" <gclemm@rational.com>


Am Donnerstag den, 12. September 2002, um 22:20, schrieb Clemm, Geoff:

> [...]
> But it would be interesting to investigate whether the
> DeltaV CHECKOUT/CHECKIN/UNCHECKOUT protocol could give clients most
> of the benefits of transactions (a non-versioning server would
> only keep the most recently checked in "version" of a resource).
> You would create an "activity" for a given transaction,
> make your changes, and then CHECKIN the activity to commit
> all the changes, or UNCHECKOUT to roll them back.

All the use cases mentioned to me for HTTP transactions can be
done with DeltaV. It would be very interesting to hear of an
authoring use case which cannot be satisfied with deltaV
features. And then I would probably try to extend deltav...

If you want to do rdbms-like transactions in WebDAV (with
READ-COMITTED transaction isolation at least), which
are also RESTful, you need to reflect the server state in
the URIs used for the transactions. And if you do that, you'd
sooner or later end up doing what DeltaV has done with
working resource, workspace and activities.

//Stefan


> Cheers,
> Geoff
>
> -----Original Message-----
> From: Gary Cowan [mailto:Gary.Cowan@Tally.Hummingbird.com]
> Sent: Thursday, September 12, 2002 3:43 PM
> To: 'Jim Whitehead'; w3c-dist-auth@w3.org
> Subject: RE: Proposal: WebDAV and transactions
>
>
>
> Well I suppose, but isn't this what wrapping updates with a 
> Lock/Unlock pair
> is intended to accomplish. I have nothing against transactions, I 
> just don't
> have any need for them spanning multiple WebDAV methods. Yet:)
>
> -----Original Message-----
> From: Jim Whitehead [mailto:ejw@cse.ucsc.edu]
> Sent: Thursday, September 12, 2002 3:24 PM
> To: w3c-dist-auth@w3.org
> Subject: RE: Proposal: WebDAV and transactions
>
>
>
> One common example is to be able to write a resource and its 
> properties in a
> single operation. You want this to be a transaction, so that the 
> resource
> doesn't get updates before the properties are written, and so that 
> if the
> properties cannot be written, the resource is reverted back to it's
> pre-write state.
>
> - Jim
>
>> -----Original Message-----
>> From: w3c-dist-auth-request@w3.org
>> [mailto:w3c-dist-auth-request@w3.org]On Behalf Of Gary Cowan
>> Sent: Thursday, September 12, 2002 12:21 PM
>> To: 'Babich, Alan'; 'Roy T. Fielding'; w3c-dist-auth@w3.org
>> Subject: RE: Proposal: WebDAV and transactions
>>
>>
>>
>> At the risk of sounding naive, I cannot understand why anyone
>> would want or
>> need transactions in a WebDAV session.
>>
>> -----Original Message-----
>> From: Babich, Alan [mailto:ABabich@filenet.com]
>> Sent: Thursday, September 12, 2002 3:11 PM
>> To: 'Roy T. Fielding'; w3c-dist-auth@w3.org
>> Subject: RE: Proposal: WebDAV and transactions
>>
>>
>>
>>
>>
>> -----Original Message-----
>> From: Roy T. Fielding [mailto:fielding@apache.org]
>> Sent: Thursday, September 12, 2002 7:01 AM
>> To: Babich, Alan
>> Cc: w3c-dist-auth@w3.org
>> Subject: Re: Proposal: WebDAV and transactions
>>
>> ...snip...
>>
>> <Alan>
>>> Between the method calls, the resources changed have to be locked 
>>> on the
>>> server.
>> </Alan>
>>
>> <Roy>
>> That's not how I described transactions.  I said that the requests are
>> collected on the server and only applied when the commit message is
>> received.  If the state has changed such that the methods are no 
>> longer
>> applicable, then the method transaction will fail on commit.
>> </Roy>
>>
>> That directly addresses the central issue, and I managed to miss that
>> somehow. >>My whole point is that when the server actually 
>> executes the
>> transaction, the server should have everything and do the entire
>> transaction
>> all at once -- retrievals, updates, and conditional processing 
>> included.<<
>> Sorry if I didn't make that clear.
>>
>> If you want to dribble the instructions for the transaction over 
>> piece by
>> piece by making separate method calls until it all gets to the server,
>> without actually doing any updates or retrievals, that's not
>> something that
>> I am concerned with much. It would be more efficient to just send 
>> over all
>> the stuff at once, but I don't think it's that big of a deal to
>> send it over
>> in pieces. So, doing that is OK with me.
>>
>> If you want the server to do some security checking and other
>> processing on
>> the individual pieces as they arrive, before actually executing 
>> the entire
>> transaction in the commit step, that's fine. That would help the 
>> client
>> pinpoint a certain subset of the possible problems in each step of the
>> transaction.
>>
>>                                  ---
>>
>> I think it would be interesting to see how the conditional
>> processing of the
>> methods is specified. How much generality is achievable without
>> getting into
>> syntax that doesn't resemble the current methods at all? To make 
>> arbitrary
>> transactions convenient, you want "program" variables, conditional
>> "statements", iteration "statements", and "subroutines" with
>> parameters. If
>> we don't go that far, perhaps a useful set of transactions could 
>> still be
>> specified.
>>
>> I also think it would be interesting to see how the results of the
>> transaction are specified. Any part of it could fail.
>>
>> Alan
>
>
Received on Friday, 13 September 2002 03:37:12 GMT

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