Staus of Primary/Foreign key?

I have implemented referential integrity in older Postgres projects
using functions. I am preparing to do a new project, aand was wondering
what the status of Primary/Foreign key implementation was?

I am starting with 6.4.2,

Thanks.

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Stan Brown stanb(at)netcom(dot)com 843-745-3154
Westvaco
Charleston SC.
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(c) 1999 Stan Brown. Redistribution via the Microsoft Network is prohibited.