Denormalization involves transforming normalized database relations into unnormalized physical tables to improve performance. This is done by reducing the number of necessary joins. While it improves speed, it also risks data duplication, wasted storage, and integrity issues. Common situations for denormalization include one-to-one relationships, many-to-many relationships with attributes, and reference data. Physical files are portions of disk storage allocated for storing records. File organization techniques determine how records are physically arranged, such as sequentially or through indexing, and affect retrieval speed, storage usage, and data protection.

2. DENORMALIZATION
AND
DESIGNING PHYSICAL
FILES
PRESENTED BY:
MAHNOOR YASEEN

3. DENORMALIZATION
• Transforming normalized relations into unnormalized physical record
specifications
• – The process of splitting or combining normalized relations into physical tables
based on affinity of use of rows and fields
• Benefits:
• Can improve performance (speed) be reducing number of table lookups (i.e
reduce number of necessary join queries)
• Costs (due to data duplication)
• Wasted storage space
• Data integrity/consistency threats

4. DENORMALIZATION
• Three common situations where denormalization may be used
Two entities with a one-to-one relationship
A many-to-many relationship with nonkey attributes
Reference data

5. A POSSIBLE DENORMALIZATION SITUATION: TWO
ENTITIES WITH ONE-TO-ONE RELATIONSHIP

6. EXAMPLE

7. CONTINUE………………..

8. DESIGNING PHYSICAL FILES
• Physical File:
• A named portion of secondary memory allocated for the purpose of
storing physical records
• Tablespace – named set of disk storage elements in which physical
files for database tables can be stored
• Extent – contiguous section of disk space
• Constructs to link two pieces of data:
• Sequential storage
• Pointers – field of data that can be used to locate related fields or
records

9. FILE ORGANIZATIONS
• Technique for physically arranging records of a file on
secondary storage
• Factors for selecting file organization:
• Fast data retrieval and throughput
• Efficient storage space utilization
• Protection from failure and data loss
• Minimizing need for reorganization
• Accommodating growth
• Security from unauthorized use

10. File Organization Continue…
How the files are arranged on the disk.
In modern RDBMS user do not have to design file
organization but may be allowed to select a file-
organization and its parameter.
Access Method:
How the data can be retrieved based on the file

11. TYPES OF FILE ORGANIZATIONS
• Sequential
• Indexed
• Hashed

12. SEQUENTIAL
• • The rows in the file are stored in sequence according to a primary key value
• • Updating and adding records may require rewriting the file
• • Deleting records results in wasted space

13. SEQUENTIAL FILE
ORGANIZATION
Records of the file are stored
in sequence by the primary
key field values

14. INDEXED FILE ORGANIZATION
• • An indexed file contains records ordered by a record key . A record key uniquely identifies a
record and determines the sequence in which it is accessed with respect to other records. .
• The rows are stored either sequentially or non-sequentially and an index is created that allows
software to locate individual rows
Indexing approaches:
• B-tree index
• Bitmap index
• Hash Index
• Join Index

15. B- TREE INDEX
Leaves of the tree are all at
same level 
consistent access time

16. HASHED FILE
ORGANIZATION
• – The address for each row
is determined using an
algorithm

18. RULES FOR USING INDEXES
1. Use on larger tables
2. Index the primary key of each table
3. Index search fields (fields frequently in WHERE clause)
4. Fields in SQL ORDER BY and GROUP BY commands

19. CONTINUE…
5. When there are >100 values but not when there are <30 values
6. DBMS may have limit on number of indexes per table and number of bytes per
indexed field(s)
7. Null values will not be referenced from an index
8. Use indexes heavily for non-volatile databases; limit the use of indexes for volatile
databases
Why? Because modifications (e.g. inserts, deletes) require
updates to occur in index files