Beginner help needed

Greetings, my name is Mark Robbins and I am new to Informix and am trying to grasp it quickly. The tutorial book I got (by Paul Mahler) seems written in a helter-skelter way that has me flipping back and forth through the book instead of a logical sequential order. Need to ask some basic stuff for anyone who has the patience to answer... Coming from a DOS world, am I correct in making these correlations? Relation = File Tuple = Record Attribute = Field In relations - I am having a hard time understanding the difference in foriegn key and primary key, if both have or are the same attribute. In the example given, what they call the foreign key acts like what I would consider the primary key and vice versa.... Anyone know the Email address of Paul Mahler? Dealing with integrity of relationship values: Book says Primary key must be unique, or have the property of being unique - then goes on to say that data in the foreign key must match the data in the primary key. okay, if that is the case, how can the primary key be unique? Please answer in public or in Email to: mark.robbins@ssanctum.com