Data/File Organization

Published: 13th December 2011
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Five of the common ways for organizing data are serial, sequential, indexed, indexed sequential and direct organization. In briefly discussion, they are:

Serial Organization:

The simplest organization scheme is serial. With serial organization, records are arranged one after another, in no particular order-other than, perhaps, the chronological order in which records are added to the file. Serial organization is commonly found with transaction data, where records are created in a file in the order in which transactions take place.

Sequential Organization:

In files that follow a sequential organization, records are arranged one after another in a predetermined order. The field on which records are sequentially organized is often called the primary key. In many sequential organization schemes, the primary key will have a unique value. For instance, no two customers will be assigned the same customer number. When the primary keys have a unique value, they can be used to access individual records in the file.

Advantages of Sequential organization:

1. Easy to organize, maintain, and understand.

2. There is no overhead in address generation. Locating a particular record requires only the specification of the key field;

3. Relatively inexpensive I/O media and devices can be used for the storage and processing of such files.

4. It is the most efficient and economical file organization in case of applications in which there are a large number of file records to be updated at regularly scheduled intervals. That is, when the activity ratio (the ratio of the total number of records in transaction file and the total number of records in master file) is very high. Applications such as payroll processing, billing and statement preparation, and bank cheque processing meet these conditions.

Disadvantages of Sequential organization

1. It proves to be very inefficient and uneconomical for applications in which the activity ratio is very low.

2. Since an entire sequential file may need to be read just to retrieve and update few records, accumulation of transactions in to batches is required before processing them.

3. Transactions must be sorted and placed in sequence prior to processing.

4. Timeliness of data in the file deteriorates while batches are being accumulated.

5. Data redundancy is typically high since the same data may be stored in several files sequenced on different keys.

A card catalog in order to determine the location of a particular book; however, in the library, the patron is usually responsible for retrieving the book.

Advantages of indexed organization:

1. Permits the efficient and economical use of sequential processing techniques when the activity ratio is high.

2. Permits direct access processing of records in a relatively efficient way when the activity ratio is low.

Disadvantages of indexed organization

1. These files must be stored on a direct access storage device. Hence, relatively expensive hardware and software resources are required.

2. Access to records may be slower than direct files.

3. Less efficient in the use of storage space than some other alternatives.

Indexed Sequential Organization:

Indexed sequential organization is a file organization scheme that allows both sequential and direct access to data. Thus, files organized in this manner must be on a direct access storage device, such as disk.

With indexed sequential organization, records are usually physically arranged on a storage medium by their primary key, just as they are with sequential organization. The difference is, however, that an index also exists for the file; it can be used to look up and directly access individual records.

Direct Organization:

Direct organization is a scheme that provides the fastest possible direct access to records. While both indexed and ISAM (indexed sequential access method) files also provide users with direct access to individual records, direct organization is typically the best when access time is critical and when updating all the records in the file in a batch is not needed.

Advantages of direct organization

1. The access to, and retrieval of a record is quick and direct. Any record can be located and retrieved directly in a fraction of a second, without the need for a sequential search of the file.

2. Transactions need not be sorted and placed in sequence prior to processing.

3. Accumulation of transactions into batches is not required before processing them. They may be processed as and when generated.

4. It can also provide up-to-the minute information in response to inquiries from simultaneously usable online stations.

5. If required, it is also possible to process direct file records sequentially in a record key sequence.

6. A direct file organization is most suitable for interactive online applications such as airline or railway reservation systems, teller facility in banking applications, etc.

Disadvantages of direct organization

1. These files must be stored on a direct access storage device. Hence relatively expensive hardware and software resources are required.

2. File updating (addition and deletion of records) is more difficult as compared to sequential files.

3. Address generation overhead is involved for accessing each record due to hashing function.

4. May be less efficient in the use of storage space than sequentially organized files.

5. Special security measures are necessary for online direct files that are accessible from several stations.


Rashid javed writes articles about computer basics such Examples of MIS and basics of computer.

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