What Is Update Anomaly?

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Joseph Russell Profile
Joseph Russell answered
An update anomaly is a condition that can occur if a database is not constructed and maintained correctly. The same condition can occur on your Windows-based PC or laptop registry if parts of a program are removed, but the registry entry for the program still exists. It is a record that remains on a database without a link, in short. And an update anomaly can cause problems such as a slow performing database and PC, and when there are too many they can cause a crash.  

Today's information technology systems are built to a large extent on relational databases. Relational databases are a collection of tables that are designed to reduce data duplication and redundancy. To what degree data duplication is eliminated is gauged in a relational database by something called data normalization. There are five degrees of normalization, with one being the lowest, and five being the highest. With a relational database in fifth normal form, there is no chance of having an update anomaly. A relational database in first normal form has a very strong chance of having an update anomaly. This has become a science within the information technology field, and every database administrator is schooled in this field and is constantly trying to avoid any update anomalies in the relational databases they are charged with maintaining. 

There are different types of data anomalies. The example cited earlier of deleting a program from your hard drive, while still having entries in your Windows registry is called a delete anomaly. If you notice that your PC or laptop is running slowly, and you have a history of installing and deleting programs from your hard drive, there a strong possibility deletion anomalies exist in your registry. To alleviate this problem, it will be necessary to buy a product from your local computer store that cleans registries of entries such as this.
Lily James Profile
Lily James answered

Logical inconsistencies can occur in tables that are not sufficiently normalized. These inconsistencies are because of various anomalies which involves data operations. This information can be expressed on multiple records and updates can result in logical inconsistencies.  

For example a change in employee address will potentially be applied to multiple records. If all the records can not be updated, the table will be left in an inconsistent state. The table will provide conflicting answers to a particular query involving employee address. This condition is known as Update Anomaly.

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