78 Part I EXAM PREPARATION After eliminating duplicates
78 Part I EXAM PREPARATION After eliminating duplicates and adding additional entities, you can then proceed with the second normal form and ensure that attributes are assigned to the most appropriate entity. Second Normal Form The first requirement of the second normal form is that it meets the requirements of the first normal form. The second requirement is that all non-key attributes are dependant on the entity key. To pass 2NF, every attribute in an entity must depend on the whole key, not just a part of it. A violation in 2NF occurs when these requirements are not met. Warehous. I. . F. Regio. I. . F. Squar. Footag. Corporat. I. . F. FIGURE 2.8 The RegionWarehouse entity violating a restriction of 2NF. To know whether an entity is violating the restrictions of 2NF, see whether the attribute is dependant on only part of the Primary Key. 2NF applies in only those entities that have a compound Primary Key and a data element is dependent on only a portion of that key. In the example case there is no violation of 2NF, so Figure 2.8 uses a separate simple example to illustrate this point. In Figure 2.8, the partial dependence is true for the Square Footage attribute in that it is dependant on only the Warehouse ID and not the Region ID. To resolve a 2NF violation, create a new entity for the partially- dependant attributes and then place these attributes inside it. Then create a key to make a relationship to the original entity. The 2NF ensures model flexibility and tries to ensure the prohibition of redundant data. Meeting the second normal form brings the design closer to an efficient model. A final set of adjustments to consider is the third normal form. Third Normal Form Third normal form shares a common objective like the other normal forms, in that its goal is to eliminate redundant data. However, it is more similar to the second normal form because it accomplishes this by cutting down interdependencies on non-key attributes. The third normal form ensures that you get the most consistency with the entity layout after you normalize the database. 3NF states that all non-Primary Key attributes must depend on the key. You cannot have any indirect or transitive dependencies, as described in the following paragraphs.
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