Hi Jaichander.
1. The OpenSocial specification defines a persistence API which allows
you to store strings as name-value pairings without a server-side back-
end -- updating and fetching this app data is handled completely
through the client-side API. If you're interested, you can read more
by following the links below.
http://code.google.com/apis/opensocial/docs/0.7/devguide.html#Persistent
http://code.google.com/apis/opensocial/articles/persistence.html
2. Server-side applications cannot currently interact with an
OpenSocial container directly -- this is where the forthcoming REST
API comes in. However, your app can have a server-side component
today. You can use gadgets.io.makeRequest in your client-side code to
store and fetch data from your server today. For example, I'm building
a photo-sharing application that posts user images to my data store
and then uses makeRequest to fetch the uploaded data when the user
clicks the Photos tab. I send all the OpenSocial-related information
needed for the request (e.g. the owner's ID) to the server as well.
3. If you have a server-side component, you can store the IDs of users
that use your application. This should allow you to roughly track the
number of users that have your application installed, although there
is no straightforward way of being notified when a user removes your
application, which could skew your statistics.
Please let me know if you have any other questions on this.
- Jason