File Organization

File organization refers to the logical sequence in which the records in the file are organized. The parameters on which files are organized are rapid access, ease of update, storage efficiency, simplicity in maintenance, and reliability. File organization can be of the following types:

• Pile
• Indexed
• Sequential
• Indexed-Sequential
• Direct or Hashed

Pile

Pile is the simplest form of file organization. In this type of organization, data is collected in the order in which it arrives. The purpose of this type of organization is collecting the data whenever it arrives and saving it. There is no specified structure or format in which the records are saved. Different records may have different fields. Pile file organization suffers from some limitations. It is not easy to retrieve data. As a result, exhaustive search is required to access the records. This kind of file organization is more suitable to be used as a temporary storage medium so that the data can be structured or organized later.

Indexed
An indexed file organization uses multiple indexes for different key fields. Whenever a new record is added to the main file, all the index files (Exhaustive, Partial) are updated. The records may vary in length. This type of file organization is used where timeliness of data is critical, for example, in an airline reservation system.

Sequential
In sequential file organization, the computer organizes data in the sequential file in the order in which data is entered into the file. The sequential file organization is the most commonly used structure for organizing large files. All records and the fields in a sequential file are of fixed format or of the same length. A unique key field, like a student ID, is used to identify a particular record.

Indexed-Sequential

The indexed-sequential file organization overcomes the disadvantages of sequential file organization. The records are organized on the basis of a key field. An index supports the random access of records. The index provides a quick search capability to quickly allow the user to get the desired record. The index also contains the key field and a pointer to the main file. When a query is executed, the index is searched to find the highest key value, which is equal to or less than the desired key value. The search continues in the main file at the location indicated by the pointer. New records in the indexed-sequential file are added to the overflow file. Then the record and index are updated in the main file.

Hashed

Hashed file organization is also called direct file organization. In a hashed file, every record is given a unique address called a hash value. This hash value is generated by using a hashing algorithm as depicted in Figure 8.5. In hashed file organization, a key field is required for each record and hashing is done on the key value to get the location of the record. This type of organization is used when rapid access is required and fixed length records are used.

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