CONCEPT OF COMPUTER FILES 3 - METHODS OF ACCESSING FILES, CLASSIFICATION OF COMPUTER FILES (SS2 NOTES)

 

CONCEPT OF COMPUTER FILES 3 

METHODS OF ACCESSING FILES, CLASSIFICATION OF COMPUTER FILES AND CRITERIA FOR CLASSIFYING COMPUTER FILE

Methods of Accessing Files

Access method is a mechanism or manner in which the records in a file may be accessed.  It defines the way the read and write operations are done. The methods of accessing files include:

• 1.       Sequential access: a sequential file access is that in which the records are accessed in some sequence i.e., the information in the file is processed in order, one record after the other. It requires the program to start writing or reading at the beginning and continues until it finds the desired data. Device like magnetic tape enforces sequential access method.
• 2.       Direct/random access: the records on the storage location can be accessed (read or written to) in any order i.e. randomly/directly. Devices such as magnetic disk storage and the main storage i.e. RAM and ROM are based on this method.
• 3.       Indexed-sequential access: this mechanism is built on the basis of sequential access. An index is created for each file which contains pointer to various records (blocks). Index is searched sequentially and its pointer is used to access the file directly.

Computer File Classifications

Computer files can be classified as follows:

• 1.       Master file: This is a computer file that is used as the authority in a given job that is relatively permanent. It is a permanent file, periodically updated, that serves as an authoritative source of data. It is an original file from which duplicates are made.
• 2.       Transaction file: It is a computer file containing relatively transient data about a particular data processing task. It is a file, especially a data file, containing transaction records, used to update the master file.
• 3.       Reference file: This is a computer file containing data, which is kept so that it can be referenced for future use. It is stable and permanent in nature.

Criteria for classifying computer file

Computer files can be classified according to the following criteria:

1.       Nature of content: files of similar contents are classified together. Examples are database file, word processed file etc.

2.       Organization method i.e. whether sequential, direct etc.

3.       Storage medium: whether they are stored in tapes, disks or any other storage devices.

4. By it extension;. For example if we see an extension like this .xls we all know that, this file is an Spreadsheet(Excel) file.

Class Activities

1. Explain any two (2) methods of classifying computer file

2. Explain direct/random access file