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Disclaimer: This presentation is prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring PartnerBaabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd
Title of the presentation
Shajeer [email protected]/shajeertwitter.com/shajeer_pkin.linkedin.com/in/
Normalization and Anomalies
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.
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.
Insert anomaly
• An Insert Anomaly occurs when certain attributes cannot be inserted into the database without the presence of other attribute
E.g.,Course _no Tutor Room Room_size En_limit353 Smith A532 45 40351 Smith C320 100 60355 Clark H940 400 300456 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.
Delete Anomaly
• A Delete Anomaly exists when certain attributes are lost because of the deletion of other attributes.
E.g.;Course _no Tutor Room Room_size En_limit353 Smith A532 45 40351 Smith C320 100 60355 Clark H940 400 300456 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.
Update Anomaly
• An Update Anomaly exists when one or more instances of duplicated data is updated, but not all.
E.g.;Course _no Tutor Room Room_size En_limit353 Smith A532 45 40351 Smith C320 100 60355 Clark H940 400 300456 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.
Normalization will help us to remove the Anomaly and create good database
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
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.
1st Normal For ExampleUn-normalized Students table:
Student#
AdvID
AdvName
AdvRoom
Class1
Class2
123 123A James 555 102-8 104-9124 123B Smith 467 209-0 102-8Normalized Students table:Student#
AdvID
AdvName
AdvRoom
Class#
123 123A James 555 102-8123 123A James 555 104-9124 123B Smith 467 209-0124 123B Smith 467 102-8
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.
2nd Normal For ExampleStudents table:Student# AdvID AdvName AdvRoom123 123A James 555124 123B Smith 467
Registration table:Student#
Class#
123 102-8123 104-9124 209-0124 102-8
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.
3rd Normal Form ExampleStudents table
Advisor table:
AdvID AdvName
AdvRoom
123A James 555123B Smith 467
Student#
AdvID
123 123A124 123B
Student# Class#123 102-8123 104-9124 209-0124 102-8
Registration table:
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.
Thanks
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