Recovery with pg_xlog

I have two questions:

 1. In Postgresql, what is the name of the exact DATAFILE under the DATA
 DIRECTORY ?

 2. We want to prepare a backup machine (for disaster management)by passing
    the pg_xlog diectory.First time we have made a base backup & restore
    the backup server by this backup.but when we want to recover from
    pg_xlog backup.Firsttime it is working,after that not.Can we recover by
    passing pg_xlog?

 Please help us in resolving this problem whereby we do not have to send
 the full DATA Directory.