Database_normalization_transcript - Modification Anomalies...

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Page 1 of 4 Modification Anomalies and Database Modification Audio Transcript This tutorial will show various types of modification anomalies that can have undesirable consequences to a database, as well as the normalization process that can help avoid these consequences. When you have a relation, even though it may meet the minimum criteria to be called a relation, it still may not be in an ideal state. Changing the data in certain relations can lead to modification anomalies or loss of data due to the data change. Let’s take a look at two types of modification anomalies. A deletion anomaly occurs when you delete one piece of information and unintentionally delete another piece of information. For example let’s say a hardware store keeps track of their customers using customer ID numbers as well as what they purchase and how much each of those things cost so they can alert customers to future sales on things they tend to purchase the most. Imagine that customer 3121 asks to be removed from the system since she is moving out of state. If you delete that customer’s row from the table, you will inadvertently lose the fact that bolts cost $4.00 as well. This is a deletion anomaly. An insertion anomaly occurs when you want to add a piece of information to your records but you require a value for a field that doesn’t exist yet. In the hardware store situation, imagine that the store gets a power sander in stock that costs $45.00. There is no way to record this information in the table until there is a customer ID to add to the row. In other words, the information can’t be added until a customer actually purchases the sander. Deletion and insertion anomalies happen here because the relation is trying to store too much connected information. It’s trying to store both the connection between customers and what they buy, and the connection between items in the store and their cost. The process of breaking up a relation to avoid these kind of anomalies is called normalization. There are a number of different levels of normalization but they are all nested together. The most basic form is first normal form, often written as 1 and F. The next level of normalization is called second normal form. Tables in second normal form have all the characteristics of those in first normal form, plus a few others. Tables in third normal form have all the criteria of second normal form plus a
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This note was uploaded on 05/23/2010 for the course DATABASE HR587 taught by Professor Prof.panchal during the Spring '10 term at Keller Graduate School of Management.

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Database_normalization_transcript - Modification Anomalies...

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