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.