Normalisation and anomalies
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This document discusses database normalization and anomalies. It defines three types of anomalies: insert, delete, and update anomalies. Examples are provided for each. The document then explains the three normal forms - 1st, 2nd, and 3rd normal form. The requirements for each normal form are defined and examples are used to illustrate how normalization reduces anomalies by eliminating redundant data and non-key dependencies from tables.
Normalisation and anomalies
- 2. Disclaimer: This presentation is prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring Partner Baabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd
- 3. Title of the presentation Shajeer pk shajeer31@gmail.com www.facebook.com/shajeer twitter.com/shajeer_pk in.linkedin.com/in/shajeerp k2@gmail.com 9544559642
- 5. ANOMALIES • Tables that have redundant data have problems known as anomalies. So data redundancy is a cause of an anomaly. • Redundancy is the duplication of the data.
- 6. There are 3 types of anomalies 1: Insert Anomaly: When you insert a record without having it stored on the related record 2: Delete Anomaly: When you delete some information and lose valuable related information at the same time. 3: Update Anomaly: Any change made to your data will require you to scan all records to make the changes multiple time.
- 7. Insert anomaly • An Insert Anomaly occurs when certain attributes cannot be inserted into the database without the presence of other attribute
- 8. E.g., Course _no Tutor Room Room_size En_limit 353 Smith A532 45 40 351 Smith C320 100 60 355 Clark H940 400 300 456 Turner H940 400 45 e.g. we have built a new room (e.g. B123) but it has not yet been timetabled for any courses or members of staff.
- 9. Delete Anomaly • A Delete Anomaly exists when certain attributes are lost because of the deletion of other attributes.
- 10. E.g.; Course _no Tutor Room Room_size En_limit 353 Smith A532 45 40 351 Smith C320 100 60 355 Clark H940 400 300 456 Turner H940 400 45 e.g. if we remove the entity, course_no:351 from the above table, the details of room C320 get deleted. Which implies the corresponding course will also get deleted.
- 11. Update Anomaly • An Update Anomaly exists when one or more instances of duplicated data is updated, but not all.
- 12. E.g.; Course _no Tutor Room Room_size En_limit 353 Smith A532 45 40 351 Smith C320 100 60 355 Clark H940 400 300 456 Turner H940 400 45 e.g. Room H940 has been improved, it is now of RSize = 500. For updating a single entity, we have to update all other columns where room=H940.
- 13. Normalization will help us to remove the Anomaly and create good database
- 14. Normalization • Normalization is the process of putting things right, making them normal. In a relational database the term has a specific mathematical meaning having to do with separating elements of data - names, addresses - into affinity groups, and defining the normal or right relationships between them. • This is database design technique which organizes tables in a manner that reduces redundancy and dependency of data(That means avoid anomaly) • Normalization is ‘standardized’ rule for making database
- 15. 1st Normal Form ,Requirements • The requirements to satisfy the 1st NF: – Each table has a primary key: minimal set of attributes which can uniquely identify a record – The values in each column of a table are atomic (No multi-value attributes allowed). – There are no repeating groups: two columns do not store similar information in the same table.
- 16. 1st Normal For Example Un-normalized Students table: Student# AdvID AdvName AdvRoom Class1 Class2 123 123A James 555 102-8 104-9 124 123B Smith 467 209-0 102-8 Normalized Students table: Student# AdvID AdvName AdvRoom Class# 123 123A James 555 102-8 123 123A James 555 104-9 124 123B Smith 467 209-0 124 123B Smith 467 102-8
- 17. 2nd Normal Form ,Requirements • The requirements to satisfy the 2nd NF: – All requirements for 1st NF must be met. – Redundant data across multiple rows of a table must be moved to a separate table. • The resulting tables must be related to each other by use of foreign key.
- 18. 2nd Normal For Example Students table: Student# AdvID AdvName AdvRoom 123 123A James 555 124 123B Smith 467 Registration table: Student# Class# 123 102-8 123 104-9 124 209-0 124 102-8
- 19. 3rd Normal Form ,Requirements • The requirements to satisfy the 3rd NF: – All requirements for 2nd NF must be met. – Eliminate fields that do not depend on the primary key; • That is, any field that is dependent not only on the primary key but also on another field must be moved to another table.
- 20. 3rd Normal Form Example Students table Advisor table: AdvID AdvName AdvRoom 123A James 555 123B Smith 467 Student# AdvID 123 123A 124 123B Student# Class# 123 102-8 123 104-9 124 209-0 124 102-8 Registration table:
- 21. Conclusion • We have seen how Database Normalization can decrease redundancy, increase efficiency and reduce anomalies by implementing three of seven different levels of normalization called Normal Forms. The first three NF’s are usually sufficient for most small to medium size applications.
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