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Most types of business data are best understood by users when they are logically organized into fields, records, and files. File processing refers to an environment in which data are physically organized into files (collection of related records). In many instances, a file in a file processing environment 'belongs' to a specific application program. In database management environments the data and files may be shared by many application programs.
Many of file management software programs used in organizations today are either written in house or developed by software vendors. A file manager is a software package that lets users and programmers organize data into files and then process those files. File managers perform such important processing tasks as information retrieval and report preparation; they are available for both large and small computers.
Data access and Organization:
Organizing and accessing data are two of the driving forces behind data management. Organizing data involves arranging data in storage so that they may be easily accessed accessing data refers to retrieving data from storage. Data organization and access are important determinants of how easily managers and users can obtain the information they need to do their jobs. Since some organization and access schemes provide faster or more flexible ways to locate individual records than others, it is important for managers to anticipate what data they and their subordinates will need when designing files and databases.
Data Accessing Methods:
There are different types of accessing data:
Sequential access:
Sequential access is a method whereby the records of file are accessed in sequential order. The records in a sequential file appear one after another in the order in which they were entered into the computer and subsequently stored on the medium. Access to any record requires access to all of the preceding records. Magnetic tape is a storage medium that is sequential in nature. To access a particular record on magnetic tape, you must read all of the preceding records first. You could use the sequential access method to record the individual student grades each week because you must access and update all of the records of the student anyway.
Direct access:
Direct access also called random access is a method in which the records in a file are stored and accessed in random order. A direct access file has a key, called a key field or access key, that lets the computer locate, retrieve and update any record in the file without reading each preceding record. A key field is a field that uniquely identifies each record. Account numbers, employee identification number and social security numbers are examples of key fields.
Indexed sequential access:
Third and final method of accessing Indexed sequential access file processing allows both sequential and direct access of the record in a file. An indexed sequential file can be set up in many ways. Basically records are stored sequentially when the indexed sequential file is created. However, where records are added to the file, they are stored out of sequence in an overflow area.
The computer keeps an index of the key fields from each record. It automatically sorts and updates the index to allow both sequential and direct access. Then it searches the index by key field to access a record. When it finds the key field, it can access the record directly using an address associated with the first key field in the sorted index and follows the rest of the index in sequential order. The sorted index allow the computer to find records in sequence no matter where they are physically located on a disk. In practice, multiple indexes usually narrow the location of each record. This type of file access does not work with tape because tape is a sequential access medium only.
