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252 Part Two  Information Technology Infrastructure


                    FIGURE 6.9   AN UNNORMALIZED RELATION FOR ORDER







              An unnormalized relation contains repeating groups. For example, there can be many parts and suppliers for each order. There is
              only a one-to-one correspondence between Order_Number and Order_Date.



                                   Normalization and Entity-Relationship Diagrams
                                   The conceptual database design describes how the data elements in the
                                     database are to be grouped. The design process identifies relationships among
                                   data elements and the most efficient way of grouping data elements together
                                   to meet business information requirements. The process also  identifies
                                     redundant data elements and the groupings of data elements required for
                                     specific application programs. Groups of data are organized, refined, and
                                   streamlined until an overall logical view of the relationships among all the
                                   data in the database emerges.
                                     To use a relational database model effectively, complex groupings of data
                                   must be streamlined to minimize redundant data elements and  awkward
                                     many-to-many relationships. The process of creating small, stable, yet
                                     flexible and adaptive data structures from complex groups of data is called
                                     normalization. Figures 6.9 and 6.10 illustrate this process.
                                     In the particular business modeled here, an order can have more than one
                                   part but each part is provided by only one supplier. If we build a relation called
                                   ORDER with all the fields included here, we would have to repeat the name
                                   and address of the supplier for every part on the order, even though the order
                                   is for parts from a single supplier. This relationship contains what are called
                                   repeating data groups because there can be many parts on a single order to
                                   a given supplier. A more efficient way to arrange the data is to break down
                                   ORDER into smaller relations, each of which describes a single entity. If we
                                   go step by step and normalize the relation ORDER, we emerge with the rela-
                                   tions illustrated in Figure 6.10. You can find out more about normalization,



              FIGURE 6.10  NORMALIZED TABLES CREATED FROM ORDER





















        After normalization, the original relation ORDER has been broken down into four smaller relations. The relation ORDER is left with only two
        attributes and the relation LINE_ITEM has a combined, or concatenated, key consisting of Order_Number and Part_Number.








   MIS_13_Ch_06 Global.indd   252                                                                             1/17/2013   2:27:43 PM
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