Farms: Group of xenapp servers, they can be combination of web interface servers, where the web site will allow the users to connect into the xen app, license servers and xen app servers itself. Farm has a single data store.
Data collector: Stores dynamic information, for each of the Zones in a farm we will have a data collector. Ex: how many users are on a server, what the users are doing, what applications are being run.
Data store: Stores static information, farm has a single data store, data store is connected by some data connection, like sql or Oracle.
With the use for both this data collector and data store we can manage a farm.
LHC : local host cache, available on each server. Its like a mini data base, for example if a XENAPP server losses its connectivity to data store then it will use the information it has in its local host cache