It deals with the storage and retrieval of data in computer usable form. The three principal methods of storing and retrieving the data are
- Sequential: Meaning that the records are stored and retrieved in a sequential order.
- Direct: Meaning that the records are not stored or retrieved in any special order.
- Indexed sequential access method: Indexed sequential is a combination of the preceding two methods where by, records are stored in sequential order but with an index that allows both sequential and random retrieval.
Each of them is suited to different applications and processing requirements.
- Sequential storage and retrieval: This method is suitable for situations in which comprehensive reports are generated. The data is generated in the sequence in which it was recorded on the storage media. The records must be accessed one after the other. The user cannot jump from one record to another. It is not accessible to the CPU until it has been loaded on to an input device. Punched cards are the earliest types of storage media which are sequential access.
- Direct access storage and retrieval: It is also called as random access, is best suited to situations in which only few records directly in no particular order. The most common approach is to use a unique element of data called a key field or key contained in each record as a basis for identifying the record and for determining which storage location on the disk the record should be stored in or retrieved from.
- Indexed sequential storage and retrieval: To access the data in either a sequential or direct fashion, a third storage and retrieval methodology was developed. Indexed sequential access method. It is used with direct access micro computer storage devices to provide maximum flexibility for processing and has proved to be the most flexible for business applications. In this approach, each file contains an index of the records stored in it. This index is some what like the index at the back of the book. When you want to look up something in the book, you check the index for the item you want and locate the page number. In the case of on the disk. The file can be indexed using any key field. Multiple indexes can be created on the same file using one or more fields as primary key field.
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