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Data Hierarchy





In data processing, storage of data is often conceptualized as a data storage hierarchy, which normally consists of the following six levels (see figure).

1.      Bit. The smallest item of data is a single binary digit (a bit), either a 0 or a 1.

2.      Character. Multiple related bits are combined to form a character (or byte). For example, the letter A, the number 4, and the special character $ are characters. Whereas the bit is the basic unit of primary and secondary storage, the character is the basic unit for human perception.

3.      Field. Multiple related characters are combined to form a field. For example, if we are processing employees’ data of a company, we may have an employee-code field, an employee-name field, hours worked field…etc. a field is a meaningful collection of related characters. It is the smallest logical data entity that is treated as a single unit in data processing. Note that a field may sometimes have a single character, such as sex code may be represented as M or F.

4.      Record. Multiple related fields are combined to form a record. For example, an employee record will contain the fields containing the data of an employee, such as employee’s code, name, hours worked…etc. Thus a record is collection of related fields that are treated as a single unit.

5.      File. Multiple related records are combined to form a file. For example, a collection of employee records of a company would be an employee file. Similarly, a collection of all the inventory records of a company forms an inventory file. Thus, a file is a number of related records that are treated as a unit. Notice that every record in a file has the same set of fields. Each record in a file is identified, for storage and retrieval purposes, by a key field whose contents are unique for each record a in a file. In case of our employee file, employee-code field may serve as the key field.

6.      Database. Multiple related files are integrated to form a database. For example, an employee database of an organization may integrate the records of multiple employee files, such as employee salary file containing details of salary and taxation information  of all employees, employee personnel information file containing details of personnel information of all employees. In a database, the data from multiple files are integrated in such a manner so that data redundancy is minimized. For example, in case of the above example of two different employee file, if in each file an employee record contains an employee address field, and if an employee changes his/her residence, the address must be changed in all the files. In a database, the two files will be integrated in such a manner that an employee’s address data is stored only once and made available to all applications. Therefore, only one update will be needed in case of change of address of an employee. In essence, a database is a collection of logically related data elements from multiple files.


Compiled By: Chaudhary Amit V.
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