[help-GIFT] Understanding MRML: undo

[Ralf Juengling]

Hi all,

I'm thinking about introducing a new MRML element to request from the
server an undo of the last query step, say "undo-query-step". The 
answer of an "undo-query-step" would be the last but one 
"query-result" message...

However, in the current version of MRML.DTD it reads:

<!ELEMENT user-data  EMPTY>
<!ATTLIST user-data command (history-backward|history-forward)
"backward"
          steps     CDATA                              #IMPLIED>


As Wolfgang explained to me, the idea with this was to let the 
client track the session state and if the user requests an 
undo-step, the server just gets notified by a message

<mrml>
        <user-data command="history-backward" />
</mrml>

say.
I wonder how this could work, since in general the session has 
a state on the server site either and this state has to be maintained 
by the server. Thus, I can imagine this to be useful only in a setting
where the session on the server site is stateless.

To conclude: I propose to introduce a new elemenent 
"undo-query-step" to request an undo of the last query step from the
server.

RFC,
Ralf