XML is a common data transfer format and many web application already use it. Below is an example of the data and it should explain most of the things you need.
<weruat>
<format>xml</format>
<locations>
<location>
<name>Free firewood</name>
<short_name>Wood</short_name>
<description>A tree fell down and I have a lot of fire wood if any one would like it give me a call at 555.555.5555</description>
<link>http://www.mysiteexample.com/item/123</link>
<address>123 Pearchtree Circle Atlanta GA</address>
<icon>http://www.mysiteexample.com/images/wood16x16.png</icon>
</location>
<location>
<name>Rent a caraige house</name>
<short_name>$500</short_name>
<description>Wonderfully renovated caraige house for rent please call 555.555.5555</description>
<link>http://www.mysiteexample.com/item/124</link>
<address>124 Pearchtree Circle Atlanta GA</address>
<icon>http://www.mysiteexample.com/images/124PearchTree16x16.png</icon>
</locations>
</weruat>