Multiple Columns Keys - Good or Bad idea?

Hi, this is not really a postgres question, more of a design question so
I hope no one minds...

I have to intergrate data from several sites, updates and new data, etc
etc, so I have come up with the following idea:

all tables will have a sequence and location column, these two columns
are the primary key. each site has it's own location number and own
sequence inserted by default.

Is this a good idea? would it be better to have just the sequence as
primary key, and make sure each site has a different sequence (ie: site
one starting at 1, site 2 starting at 10,000,000)

The second idea seems a bit kludgy to me, but if I go the first way I
have two have two cloumns as links in each table, you know SELECT * FROM
foo WHERE key1=77 and key2=4

Stuck and awaiting help...

Thanks

--

Rob Brown-Bayliss
---======o======---