\ans

The database will reserve the specified amount of memory for each
record regardless of the values in that record.  If you set up a state
field with a length of 500 characters, and the user always puts in two
letter abbreviations, the DBMS will 'pad' the field with 498 spaces.
All of those spaces will be held in memory and on the disk each time
the record is accessed, and waste a lot of valuable real estate on the
disk and memory.  Don't make fields any bigger than you have too, but
don't make them too small.


\ans

The card catalog was actually 3 copies of the same database, sorted on different fields!  The author catalog is sorted on the author field.  (I don't have to tell you the others, do I?)


\ans

Because it makes an {\em ideal} key field.  Every citizen in the
United States has one, and they all are different.  They also all have
the same format.  Social Security Numbers were never intended for this
general use beyond government databases, but it has become very
widespread.


\ans

The type of business, followed by the name of the business

