Session Beans - Table

How the Container knows which table to look for the fields for CMP !
Where do you define it ?
How many descriptors for Entity Beans !
{only ejb-jar.xml + one for the container}
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How I get into this Trouble !
I did a Session Beans by looking at the Wrox Book ! It worked !
(Deployed on Jboss)
And then I did a Entity beans using Wrox !
Find that they have not bothered to give the xml descriptor (ejb-jar.xml)
Referred the Roman's Book ! They have a descriptor for BEA not for Jboss !
Went to Jboss site, they have a descriptor ! but not clear !