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Process for evaluating and correcting table structures to reduce data anomalies, redundancies, and inconsistencies |
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First Normal Form Second Normal Form Third Normal Form BCNF Fourth Normal Form Fifth Normal Form Domain Key Normal Form |
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The slower the database response |
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Data inconsistencies Wasted data entry time and storage space |
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Abnormal data relationships |
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Insert anomaly Update anomaly Deletion anomaly |
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Main source of data anomalies |
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Start with a big table Break into a set of smaller tables that are related Each table represents a single entity to eliminate data redundancies |
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Groups of multiple entries of the same type that exist for any single key attribute occurrence Cause null values |
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No repeating groups, and the primary key is identified Enter in values for all of the null values, then identify a primary key Primary key can't have redundancies and must be an identifier of other columns Draw a dependency diagram |
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An attribute depends on only a portion of the primary key |
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Two none key attributes that depend on each other Cause data anomalies |
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How to convert table from 1NF to 2NF |
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Eliminate partial dependencies |
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How to convert table from 2NF to 3NF |
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Eliminate transitive dependencies |
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How to remove partial dependencies |
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Write each key component of a separate line Write composite key on the last line Assign dependent attributes |
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Table is already in 2NF when |
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It is in 1NF and includes no partial dependencies so the table has a single primary key |
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When you remove a transitive dependency... |
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keep the determinant in the original table, otherwise you will lose that link |
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Every determinant in table is a candidate key |
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It is is 2NF And no multiple set of multi-valued dependencies |
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Go from 3rd form to 2nd form to save time on queeries |
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