PostgreSQL catalogues: finding the primary key

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I'm trying to get Keystone to work with PostgreSQL.  One of the PHP
functions they use retrieves attribute information on a table to find
the primary key (actually, it retrieves attribute information on a
column; it is very MySQL-oriented).

I can't figure out which set of catalogues I need to search to find
this information.  Can someone point me in the right direction?

roland

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Roland B. Roberts, PhD                  Custom Software Solutions
roberts@panix.com                           101 West 15th St #4NN
                                               New York, NY 10011