Sequence question.

I'm working on an idea that uses sequences.

I'm going to create a table like this:

id serial,
sequence int,
keyword varchar(32),
text text

for every keyword there will be a uniq sequence for it eg:

id, sequence, keyword
1, 1, foo, ver1
2, 1, bar, bar ver1
3, 2, foo, ver2
4, 2, bar, bar ver2
etc...

I could have one sequence for all keyword which would be 1,3, etc... I 
would be prefer to have them in sequence.  I'm sure someone has ran into 
this before, any ideas?

Anthony.