Download LM4 PowerPoints Slides

IT 5433 LM4
Physical Design
Learning Objectives:
• Describe the physical database design process
• Explain how attributes transpose from the logical to physical model
• Describe the different types of file organizations
• Describe the different types of indexing
• Describe the pros and cons denomalization
Physical Design Database Process
• Physical database design translates the logical data model into a set
of SQL statements that define the database.
• For relational database systems, it is relatively easy to translate from a
logical data model into a physical database.
http://ewebarchitecture.com/web-databases/physicaldatabase-design
Physical Design Database Process
• Entities to Tables
• Relationships to Foreign Keys
• Attributes to Columns
• Primary Unique Identifiers to the Primary Key
• Unique Identifiers to Unique Keys
https://docs.oracle.com/cd/A81042_01/DOC/server.816/a7699
4/physical.htm
How Attributes Transpose from the Logical to
Physical Model
• During the physical design process, you convert the data gathered
during the logical design phase into a description of the physical
database, including tables and constraints.
• Physical design decisions, such as the type of index or partitioning
have a large impact on query performance.
https://docs.oracle.com/cd/A81042_01/DOC/server.816/a7699
4/physical.htm
How Attributes Transpose from the Logical to
Physical Model
Logical Design Compared with Physical Design
https://docs.oracle.com/cd/B28359_01/server.111/b28313/ph
ysical.htm
File Organization
Types:
• Sequential
• Indexed
• Hashed
https://www.dlsweb.rmit.edu.au/toolbox/knowmang/content/
physical/file_organisation.htm#Organising
File Organization
• Sequential - Records are organised sequentially according to primary key value in
an ordered sequential file. It is easy to locate and read from the file in order of
key value
• Indexed - The index file contains key value(s) that can be matched with key values
in one or more records. The index also contains the disk address of the record.
• Hashed - In hashed file organisation the address of each record is determined
using a hashing algorithm.
https://www.dlsweb.rmit.edu.au/toolbox/knowmang/content/
physical/file_organisation.htm#Organising
Indexing
• Indexes are optional structures associated with tables or clusters. In
addition to the classical B-tree indexes, bitmap indexes are very common
in data warehousing environments. Bitmap indexes are optimized index
structures for set-oriented operations.
• Indexes are just like tables in that you can partition them, although the
partitioning strategy is not dependent upon the table structure.
Partitioning indexes makes it easier to manage the data warehouse during
refresh and improves query performance
https://docs.oracle.com/cd/B28359_01/server.111/b28313/ph
ysical.htm#i1006325
Pros and Cons of Denormalization
Denormalized databases fair well under heavy read-load and when the application is read
intensive.
This is because of the following reasons:
• The data is present in the same table so there is no need for any joins, hence the selects are very
fast.
• A single table with all the required data allows much more efficient index usage. If the columns
are indexed properly, then results can be filtered and sorted by utilizing the same index. While in
the case of a normalized table, since the data would be spread out in different tables, this would
not be possible.
http://www.ovaistariq.net/199/databases-normalization-ordenormalization-which-is-the-better-technique/
Pros and Cons of Denormalization
• Because the data is duplicated, the updates and inserts become
complex and costly.
• Having said that neither one of the approach can be entirely
neglected, because a real world application is going to have both
read-loads and write-loads.
http://www.ovaistariq.net/199/databases-normalization-ordenormalization-which-is-the-better-technique/
Links:
• https://docs.oracle.com/cd/A81042_01/DOC/server.816/a76994/phy
sical.htm
• http://ewebarchitecture.com/web-databases/physical-databasedesign
• http://www.ovaistariq.net/199/databases-normalization-ordenormalization-which-is-the-better-technique/
• https://docs.oracle.com/cd/B28359_01/server.111/b28313/physical.
htm#i1006325
• https://www.dlsweb.rmit.edu.au/toolbox/knowmang/content/physic
al/file_organisation.htm#Organising