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The data hierarchy comprises bits, bytes, fields, records, and files, which are the elements of a database. Computers, as we have said, work on the principle that electricity may be on or off, high-voltage or low-voltage, or present or absent.
Thus, individual items of data are represented by 0 for off and 1 for on. A 0 or 1 is a bit. A unit 8 bits is a byte; it may be used to represent a letter, number, or other value, such as A, 3, or ?. Bits and bytes are the building blocks for representing data, whether it is being processed, stored, or telecommunicated.
Data can be grouped according to a hierarchy of categories, each increasingly complex. The data storage hierarchy consists of the levels of stored data: bits, bytes (characters), Fields, records, files, and databases. Bits and bytes are what the computer hardware deals with, and you need not be concerned with them. You will, however, be dealing with characters, fields, records, files, and databases.
Byte (character): A byte is a group of 8 bits. A character may be but is not necessarily the same as a byte. A character is a single letter, number, or special character such as ; , $ or %.
Field: A field is a unit of data consisting of one or more characters. For example, a field is your name, your address, or our social security number. Not: One reason the social security number is often used to identify people-for good or for ill-is that, unlike many names, it is a distinctive (unique) field. Thus, it can be used to easily locate information about you only. Such a key is called a key field; this is a field that is chosen to uniquely identify a record so that it can be easily retrieved.
Record: A record is a collection of related fields. An example of a record would be our name and address and social security number.
File: A file is a collection of related records. For example, a file is collected data on everyone employed in the same department of a company, including all names and addresses and social security numbers.
Database: A database is a collection of related files. Any company’s database might include files on all past and current employees in all departments. There would be various files for each employee: payroll, retirement benefits, sales quotas and achievements (if in sales), and so on. A database may be fairly small, contained entirely within your own personal computer. Or it may be massive, available online to you from an information service through computer and telephone connections.