Database System:
As stated earlier, a database is a collection of related data that is organized in a proper form to make access easier. DBMSs were first introduced during the 1960s and since then, it has undergone a lot of changes. Before understanding DBMSs, it is important to understand data hierarchy, the components of a database system, and file organization.
Data Hierarchy
Hierarchy of data refers to organizing data systematically and in a proper sequence. From the user's perspective, data can be logically organized into characters, fields, records, files, and databases. Each of these data elements are discussed in detail here:
Character
A character is the most basic element of data that can be observed and manipulated. It consists of a single alphabet, number, or symbol.
Field
A field consists of a group of characters. For example, the grouping of the characters in a person's name forms a name field, and the grouping of numbers in a sales figure forms a sales amount field.
Record
Related fields of data are grouped to form a record. For example, a payroll record consists of data fields such as name, salary, etc. In fixed-length records, the size of data fields is limited whereas in variable-length records, the size varies.
File
A group of related records constitute a data file. An employee file would contain the records of all the employees of a firm. Files are classified based on their permanence. That is, some files are temporary in nature as they undergo updation from time to time, and others are permanent. Let us take the example of a payroll monthly transaction file and a payroll master file. The transaction file contains records of all transactions occurring during a period and might be used periodically to update the master file. Master files contain a permanent record of files. On the other hand, a history file is an obsolete file which is used for backup purposes. It is also called archival storage.
Database
Data that was previously stored in files is now consolidated and stored in databases. A database is a collection of logically related records and files. The data stored in a database is independent of the application programs using it. For example, instead of storing payroll details in separate files, it can be consolidated and stored in a database.
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