File organization in database, how to organize file in database, what is file organization?

1. 1/16/2017 File management in SQL
Database / BS-IT 2nd
Submitted to : Ma’m Mehwashma Amir
Afrasiyab Haider
16-ARID-02

2. 1 File management in SQL
AfrasiyabHaider|16-ARID-02
File Organizationin database:
In a database we have lots of data. Each data is grouped into
related groups called tables. Each table will have lots of related records. Any user will see these
records in the form of tables in the screen. But these records are stored as files in the memory.
Usually one file will contain all the records of a table. If they are not stored as tables, there and
our SQL queries will not work. We need some accessing methods. To access these files, we need
to store them in certain order so that it will be easy to fetch the records. It is same as indexes in
the books, or catalogues in the library, which helps us to find required topics or books
respectively. Storing the files in certain order is called file organization.
The main objective of file organization is
 Optimal selection of records i.e.; records should be accessed as fast as possible.
 Any insert, update or delete transaction on records should be easy, quick and should not
harm other records.
 No duplicate records should be induced as a result of insert, update or delete
 Records should be stored efficiently so that cost of storage is minimal.
Types of file organization:
 Sequential File Organization
 Indexed File Organization
 Hashed File Organization
 Sequential file organization:
It is one of the simple methods of file organization. Here each file/records are stored one
after the other in a sequential manner. This can be achieved in two ways:
1. Records are stored one after the other as they are inserted into the tables. This method is
called pile file method. When a new record is inserted, it is placed at the end of the file.
In the case of any modification or deletion of record, the record will be searched in the
memory blocks. Once it is found, it will be marked for deleting and new block of record
is entered.
2. A sequential file contains records organized by the order in which they were entered. The
order of the records is fixed.
3. Records in sequential files can be read or written only sequentially.
4. After you place a record into a sequential file, you cannot shorten, lengthen, or delete the
record. However, you can update (REWRITE) a record if the length does not change.
New records are added at the end of the file.

3. 2 File management in SQL
AfrasiyabHaider|16-ARID-02
5. If the order in which you keep records in a file is not important, sequential organization is
a good choice whether there are many records or only a few. Sequential output is also
useful for printing reports.
 Indexed File Organization:
1. 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.
2. Each record contains a field that contains the record key. A record key for a record
might be, for example, an employee number or an invoice number.
3. An indexed file can also use alternate indexes, that is, record keys that let you access
the file using a different logical arrangement of the records. For example, you could
access a file through employee department rather than through employee number.
4. The possible record transmission (access) modes for indexed files are sequential,
random, or dynamic. When indexed files are read or written sequentially, the
sequence is that of the key values.
5. EBCDIC consideration: As with any change in the collating sequence, if your
indexed file is a local EBCDIC file, the EBCDIC keys will not be recognized as such
outside of your COBOL program. For example, an external sort program, unless it
also has support for EBCDIC, will not sort records in the order that you might expect.
 HashedFile Organization:
1. Records need not be sorted after any of the transaction. Hence the effort of sorting is
reduced in this method.
2. Since block address is known by hash function, accessing any record is very faster.
Similarly updating or deleting a record is also very quick.
3. This method can handle multiple transactions as each record is independent of other.
i.e.; since there is no dependency on storage location for each record, multiple records
can be accessed at the same time.
4. It is suitable for online transaction systems like online banking, ticket booking system
etc.