• Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint
Share this Page URL
Help

4. Database Design Principles > 4.6. Third Normal Form

Third Normal Form

Second normal form is good, but we can do better. We have seen that if a table scheme is in second normal form, then no strictly informational attribute depends on a proper subset of a key. However, there is another undesirable possibility. Let us illustrate with an example.

Consider the following table scheme and assume, for the purposes of illustration, that no two books with the same title have the same publisher:

{Title,PubID,PageCount,Price}

The only key for this table scheme is {Title,PubID}. Both PageCount and Price are informational attributes only.

Now, let us assume that each publisher decides the price of its books based solely on the page count. First, we observe that this table is in second normal form. To see this, consider the proper subsets of the key. These are:


PREVIEW

                                                                          

Not a subscriber?

Start A Free Trial


  
  • Creative Edge
  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint