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Q4 - arranged is immaterial in direct access methods It is...

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Q4. Explain the various file-accessing techniques in data management system. Also state the advantages and limitations of each technique. Ans. FILE-ACCESS METHODS Data items are organized into files, and these files are recorded on a secondary storage medium such as disk or tape and accessed. The data items or files placed in secondary storage must be organized in many ways before they can be stored and retrieved. Three common ways are: 1. Sequential access file 2. Direct access file 3. Indexed-sequential file A Sequential access file is one in which the records are stored in either ascending or descending order and accessed one after the other. Magnetic tape is a storage medium that is sequential in nature. To access a particular record all the records preceding it in the file must be accessed first. It can’t be accessed directly. A Direct access file is one in which a record is read or accessed directly from a disk without accessing or reading all preceding records. The sequence in which the records are
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Unformatted text preview: arranged is immaterial in direct access methods. It is the fastest of the three access methods but is relatively costly in terms of hardware and software required. The records in Indexed sequential access file are organized in sequence and an index table is used to speed up access to the records without requiring a search of the entire file. The records of the file can be stored in random sequence but the index table is in the sorted sequence on the key value. Through this a file can not only be accessed in random manner but also in sequential manner too. Since, the index table is in sorted sequence on the key value, the file management system simply access the data records in the order of the index values. Thus, index sequential files provide the user sequential access, even though the file management system is accessing the records in a physically random manner....
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