Rules of Data Normalization Essay Example For Students

Rules of Data Normalization Essay pic 1. Eliminate Repeating Groups Make a separate table for each set ofrelated attributes, and give each table a primary key. 2. Eliminate Redundant Data If an attribute depends on only part of amulti-valued key, remove it to a separate table. 3. Eliminate Columns Not Dependent On Key If attributes do notcontribute to a description of the key, remove them to a separatetable. Moving the known databases into a seperate table helps a lot. Separating the repeating groups of databases from the member information results in first normal form. The MemberID in the database table matches the primary key in the member table, providing a foreign key for relating the two tables with a join operation. Now we can answer the question by looking in the database table for DB2 and getting the list of members. 2. Eliminate Redundant DataIn the Database Table, the primary key is made up of the MemberID and the DatabaseID. This makes sense for other attributes like Where Learned and Skill Level attributes, since they will be different for every member/database combination. But the database name depends only on the DatabaseID. The same database name will appear redundantly every time its associated ID appears in the Database Table. Suppose you want to reclassify a database give it a different DatabaseID. The change has to be made for every member that lists that database! If you miss some, youll have several members with the same database under different IDs. This is an update anomaly. Or suppose the last member listing a particular database leaves the group. His records will be removed from the system, and the database will not be stored anywhere! This is a delete anomaly. To avoid these problems, we need second normal form. To achieve this, separate the attributes depending on both parts of the key from those depending only on the DatabaseID. This results in two tables: Database which gives the name for each DatabaseID, and MemberDatabase which lists the databases for each member. Now we can reclassify a database in a single operation: look up the DatabaseID in the Database table and change its name. The result will instantly be available throughout the application. 3. Eliminate Columns Not Dependent On KeyThe Member table satisfies first normal form it contains no repeating groups. It satisfies second normal form since it doesnt have a multivalued key. But the key is MemberID, and the company name and location describe only a company, not a member. To achieve third normal form, they must be moved into a separate table. Since they describe a company, CompanyCode becomes the key of the new Company table. The motivation for this is the same for second normal form: we want to avoid update and delete anomalies. For example, suppose no members from the IBM were currently stored in the database. With the previous design, there would be no record of its existence, even though 20 past members were from IBM!4. Isolate Independent Multiple Relationships This applies primarily to key-only associative tables, and appears as a ternary relationship, but has incorrectly merged 2 distinct, independent relationships. Canterbury Tales Interpretive EssayThe way this situation starts is by a business request list the one shown below. This could be any 2 M:M relationships from a single entity. For instance, a member could know many software tools, and a software tool may be used by many