HRP1001, PA0000,PA0001

Hi HR experts,

I am an abaper and i am given a assignment on HR. I am to deal with infotypes 0000, 0001 and hrp1000 and hrp1001. whilst i was goin thru threads for the above infotypes, few things kept haunting me and after i cudnt find nething for it that wud make me clear, m writing this post. I want to know what does the following fields do.

plans or position, otype, objid, plvar, sobjid, relat and also i dint understand why are few fields concatenated, a citation with example wud be great help.

thanks in advance,

Gaurav