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Saturday, October 8, 2016

Sequential File Organization in DBMS-Tutorial

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:
  • Records are stored one after the other as they are inserted into the tables. This method is calledpile 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.
Inserting a new record:
In the diagram above, R1, R2, R3 etc are the records. They contain all the attribute of a row. i.e.; when we say student record, it will have his id, name, address, course, DOB etc. Similarly R1, R2, R3 etc can be considered as one full set of attributes.
  • In the second method, records are sorted (either ascending or descending) each time they are inserted into the system. This method is called sorted file method. Sorting of records may be based on the primary key or on any other columns. Whenever a new record is inserted, it will be inserted at the end of the file and then it will sort – ascending or descending based on key value and placed at the correct position. In the case of update, it will update the record and then sort the file to place the updated record in the right place. Same is the case with delete.
Inserting a new record:

Advantages of Sequential File Organization

  • The design is very simple compared other file organization. There is no much effort involved to store the data.
  • When there are large volumes of data, this method is very fast and efficient. This method is helpful when most of the records have to be accessed like calculating the grade of a student, generating the salary slips etc where we use all the records for our calculations
  • This method is good in case of report generation or statistical calculations.
  • These files can be stored in magnetic tapes which are comparatively cheap.

Disadvantages of Sequential File Organization

  • Sorted file method always involves the effort for sorting the record. Each time any insert/update/ delete transaction is performed, file is sorted. Hence identifying the record, inserting/ updating/ deleting the record, and then sorting them always takes some time and may make system slow.

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