I am trying to setup a system for automating certain tasks in my home.

I am thinking of a solution wherein a server side application would be able to send/receive commands/data to Arduino (attached with Arduino Ethernet Shield) via the web.

Here the Arduino may both act as a sensor interface to the server application or command executor interface for the server app.

E.g. (user story):

1. The overhead water tank in my house has a water level sensor attached with Arduino (attached with Arduino Ethernet Shield).

2. Another Arduino (attached with Arduino Ethernet Shield) is attached with a relay/latch. This relay/latch is then connected to a water pump.

3. Now the server side application on the web is able to get/receive water level information from the Arduino on the water tank.

4. Depending on the water level information received, the web application should send suitable signals/commands to Arduino on water pump to switch 'ON' or switch 'OFF' the water pump.

Now for such a system to work across the web, I am thinking of using one of the type of solutions in order of my priority:

1. Using XMPP for communication between server application and Arduino.

2. Using HTTP polling.

3. Using HTTP hanging GET.

For solution number 1, I need to implement a XMPP client that would reside on Arduino.

Is it possible to write a XMPP client small enough to reside on an Arduino?

If yes what are the minimum possible XMPP client functionality that I need to write for Arduino, so that it would be able to contact XMPP servers solutions like GTalk, etc.?

For solution number 2 and 3 I need guidance in implementation.

Also which solution would be cost effective and easily extendable?