Subject: Proposal: WebDAV and transactions

From: "Pill, Juergen" <[email-masked]>
Date: Mon, 2 Sep 2002 12:24:17 +0200

Hello,

The current WebDAV specifications deal with a transactional support on a
method base only. Either a single WebDAV method is completely and
successfully executed, or the method is not executed at all (e.g. a
PropPatch command will either modify all requested properties or none of
them). A transactional support spanning multiple WebDAV methods is currently
not specified.
Multi user requirements are either handled in separate workspaces (Delta-V)
or via the Lock method.
During our discussion on the JSR 170 (Content Management API) implementation
on top of WebDAV, we believe that we require longer transactions spanning
multiple separate WebDAV methods. (This issue was already partially
discussed in the Batch method thread). Do you also fell the need/requirement
to get a standard on the way, concerning a transactional WebDAV protocol
extension?

A possible use case would be:
An author wants to modify an html page. To successfully do so, he will PUT
the updated html page back, PROPPATCH and UNLOCK it, DELETE all bitmap
files, which are not references any more, and PUT (create) the newly
referenced bitmaps files. If he wants to ensure, that either all his changes
do apply (or none of them) he would surround those method call with an
TA-BEGIN and a TA-COMMIT method call. If the author would be an API (e.g.
JSR 170) exposing the TA functionality to an application, we believe this
feature to be mandatory.

A possible (starting) specification could be:
WebDAV defines 3 additional methods: TA-BEGIN, TA-COMMIT and TA-ABORT. The
TA-BEGIN method will return a TA token (e.g. via an XML response body). This
TA token will be send to the following WebDAV methods, which are part of
this transaction (e.g. via an additional header). The TA-COMMIT or TA-ABORT
method will either commit or abort the transaction and invalidate the TA
token. 
If and when an open TA, which is not used any more, is aborted, could be
controlled similar to the lock method timeout header.
All WebDAV methods, which either do not posses a TA token, or posses an
invalid token are handled as today (the method is executed within its own
TA), this would ensure upward compatibility.
This extension would be optional, if a server supports the TA methods, it
will state this in the OPTIONS request (similar to Delta-V).

Does this make sense?

Best regards
Juergen Pill

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From: "B. Shadgar" <[email-masked]>
Date: Mon, 02 Sep 2002 12:35:15 +0100

> will state this in the OPTIONS request (similar to Delta-V).

Juergen,

It is what exactly I was thinking about. I've got another scenario of possible
using TA- methods you have proposed. I need those transaction methods since I
am dealing with accessing the database through the web based on the WebDAV
protocol. In other words, I've almost prepared an application which accesses to
the database and considers the database data model as WebDAV resources. With
all methods are provided by WebDAV and other WG + Batch method , I am able to
send almost all SQL queries into the server in form of WebDAV methods. But some
statements like commit, rollback, savepoint can not be implemented by WebDAV
methods, and it is exactly what you suggesting; TA-COMMIT, TA-ABORT and
TA-BEGIN.  This application can be another possible use case of those three
methods + Batch method which is discussed already but hasn't been accepted as a
WebDAV method.

If I want to complete your proposal from my point of view I would say: Since
the WebDAV claims to encompass all kind of web resources representing by URI,
databases resource can be considered as its resource and therefore to support
database operation we would need TA- Methods  as well as Batch Method.

Regards,
Bita