ABAP developers should not bother about the cluster and 
pool tables becoz we ABAPiers are mostly concerned with 
TRANSparent tables as it holds application data which is 
much more important to run a organization.

IF ur interested then go for R & D by joining SAPLABS there 
you get a better exposure to do this things..

Best of luck . anyways don't try to use joins between 
altogether different tables it won't work.