A link is a navigation tool which allows you to follow a "one-to-many"
or "many-to-one" relationship from one form to another.

Every link is stored as a record in the pfm_link table, which has the
following attributes:

    - linkname : the name of the link, which is displayed on
      a link button on the "fromform";

    - fromform : the name of the form from which the link
      originates;

    - toform : the name of the form to which the link leads;

    - sqlwhere : the "WHERE"-clause which is used to open the
      "toform" and in which the value of an attribute of the
      "fromform" may be represented by $(attrib-x), where
      'attrib-x' is the name of the attribute;

    - orderby : an 'order by' clause which determines the order of the
      records in the 'toform';

    - displayattrib : a space separated list of
      attributes of the 'fromform', the value of which is displayed on
      the 'toform' to remind the user from which record the link
      originated.

Note: Postgres Forms does not provide any checks to safeguard
      the referential integrity of the data base in case of updates or
      deletions. However, postgreSQL provides these functions as
      'foreign key' table constraints (see postgreSQL documentation).