storing/maintaining a collection in memory during sevice cal

Question

Hi,
I have a dictionary. I will be feeling that dictionary from
database later on. For now I don'nt have a database. So for the time
being I want to actually maintain the dictionary data.
Like from front end I will be adding/deleting items. I want to maintain
that in backend and update the UI as per the user action that is Save or delete. (Only for that instance.). I will have a service call from front end to backend.
Note: I want it only for that instance. Like if user closes the application, then I don'nt need to maintain.
Is this posible ??
Regards,