File Organization

File Organization

A file is named collection of
related information that is recorded on secondary storage such as magnetic
disks, magnetic tables and optical disks.

A database consist of a huge amount of data. A user can see that the data is stored in form
of tables, but in actual this huge amount of data is stored in physical memory
in form of files.

File Organization refers to the
logical relationships among various records that constitute the file. In simple
terms, Storing the files in certain order is called file Organization. 

File
Structure refers to the format of the label and data blocks and of any
logical control record.

Types of File Organizations –

·        
Sequential File
Organization

·        
Heap File
Organization

·        
Hash File
Organization

·        
B+ Tree File
Organization

·        
Clustered File
Organization

These particular
methods have advantages and disadvantages. It is all upon the programmer to
decide the best suited file Organization method according to the requirements.

Physical
database design Issues

Physical
database design is concerned with transforming the logical database structures
into an internal model consisting of stored records, files, indexes and other
physical structures.

Physical
database design is the process of implementing the logical data model in a
DBMS.

The
process of implementing a relational data model in a DBMS involves creating a
set of relations.

The
decisions made during the physical database design stage affect the speed of
the database, the accessibility of the database, the security implemented on
the database and the user-friendliness of the database.

Issues
affect physical design is given below:

Before
the physical database design can be performed it is important to understand:

1.
The maximum size of the database. The size of a database is determined
by how many relations are in the database and how much data is held in each
relation. The amount of data in the database will determine how long operations
take to perform.

•
The amount of data in the database will determine the type of DBMS that must be
used.

For
example, a small database may be implemented on a simple DBMS but a large
database will require a complex DBMS.

•
The amount of data also determines the amount of disc space required to store
the data.

 For example, a small database will require a
small amount of disc space while a large database will require large amounts of
disc

storage.

•
The time it takes to execute queries or updates in the database is determined
by the amount of data.

 For example, an update that requires all the
tuples in a large relation to be changed will take longer than an update that
changes all the tuples in a small relation.

•
The time it takes to transfer the data between systems.

 For example, transferring a large amount of
data between the database server and the user’s machine will take longer than
transferring a small amount of data.

2.
The use that will be made of the database. If a database is queried
often then it will have to be designed to answer a large number of queries
quickly. If data is added to the database often then it will have to be
designed to handle many inserts quickly.

•
The use of the database determines which parts of the database are important
and will be accessed often.

•
A data item that is accessed every hour should normally be quicker to access
than a data item that is accessed once a year.

Once
the database designer knows the size of database and how it will be used, he or
she must decide the most efficient method of implementing the database.