ary for color, another for number of
        doors, another for number of passengers, and so forth. Of course, you
        will need a unique 
            
            <span>key extractor function</span>
        for each such secondary database. You do
        all of this using the concepts and techniques described throughout this
        chapter.
    </p>
      <p>
        Once you have created this primary database and all interesting
        secondaries, what you have is the ability to retrieve automobil