Method of Accessing Files

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In today’s Computer Science class, We will be learning about Methods of Accessing System Files. We hope you enjoy the class!

 

 

FILE ORGANIZATION

File organization is a way of organizing the data or record in a file. It does not refer to how files are organised in folders but how the contents of a file are added not accessed. There are several types of file organisation methods. The most common of them are sequential, relative and indexed. They differ in how easily records can be accessed and the complexity in which records can be organized. In a modern computer system, files are typically accessed using names also known as the file name. Most computers organize files into hierarchies using folders, directories or catalogues. The concept is the same irrespective of the terminology used. Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as subfolders. Subfolders can contain still more files and folders and so on, thus building a tree-like structure in which one “master folder” can contain any number of levels of other folders and files.

 

There are 5 methods of organizing files

These are:

1. sequential
2. line – sequential
3. indexed – sequential
4. inverted list
5. direct and hashed access organization.

 

TYPES OF FILE ORGANISATION

1. SERIAL: Records in a series are inserted as they arrive. The file is usually read serially from beginning to end. Searching individual records is difficult because in each case the entire file must be read. Serial files are usually used for temporary storage of transaction data.
2. SEQUENTIAL FILES: Records are arranged in key-value order, usually ascending but it can also be in descending order. The file is usually read in the order in which it is written, from beginning to the end. The great strength of sequential files is that two sequential files which share a key field and are ordered in the same way can be merged very efficiently.
3. INDEXED SEQUENTIAL FILES: Many applications require a mixture of low and high hit rate. In these cases, neither the sequential nor direct organisation is adequate. Indexed sequential files are ideal for such applications. Because the records are organised sequentially, high hit rate processing is well supported. Direct access of individual records for low hit rate application is provided by an index.
4. RANDOM OR DIRECT FILES: With direct or hashed access, a portion of disk space is reserved and a “hashing” algorithm computes the record address. So there is additional space required for this kind of file in the store. Records are placed randomly throughout the file and are accessed by addresses that specify their disc location.

A sequential file contains records organised in the order they are entered. The order of the record is fixed.

 

 

 

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In our next class, we will continue learning about Handling Computer Files. We are very much eager to meet you there.

 

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