A data dictionary is a database file that contains the name, type, range of values, source, and authorization for access for each data element in a database. It also indicates which application programs use that data so that when a data structure is contemplated, a list of affected programs can be generated. The data dictionary may be a stand-alone information system used for management or documentation purposes, or it may control the operation of a database.
This information may include:
i. Codes describing the data item‘s length, data type and range.
ii. Identification of the source documents used to create the data item.
iii. Names of the computer files that store the data item.
iv. Names of the computer programs that modify the data item.
v. The identity of the computer programs or individuals permitted to access the data item for the purpose of file maintenance, upkeep or inquiry.
vi. The identity of the computer programs or individuals not permitted to access the data item.
A data dictionary is a computer file that contains descriptive information about the data items in the files of a business information system. Thus, a data dictionary is a computer file about data. Each computer record of a data dictionary contains information about a single data item used in a business information system. This information may include:
1. Codes describing the data item‘s length (in characters), data type (alphabetic, numeric,
alphanumeric, etc) and range (e.g. values from 1 to 99 for a department code)
2. The identity of the source document(s) used to create the data item.
3. The names of the computer files that store the data item.
4. The names of the computer programs that modify the data item.
5. The identity of the computer programs or individuals permitted to access the data item for the purpose of file maintenance, upkeep, or inquiry.
6. The identity of the computer programs or individuals not permitted to access the data item.
As new data fields are added to the record structure of a business file (e.g., adding a ‗reorder quantity‘ filed to the inventory record), information about each new data item is used to create a new computer record in the data dictionary. Similarly, when new computer programs are created those access data items in existing files, the data dictionary is updated to indicate the data item these new programs access. Finally, when data filed are deleted from the structure of file records, their corresponding records in the data dictionary are dropped.
Data dictionaries have a variety of uses. One is as a documentation aid to programmers and system analysts, who study, correct, or enhance either the database or the computer programs that access it. A data dictionary is also useful for file security – i.e., to prohibit certain employees from gaining access to sensitive payroll data.
Accountants and auditors can also make good use of data dictionary. For example, a data dictionary can help establish an audit trail because it can identify the input sources of data items, the computer programs that modify particular data items, and the managerial reports on which the data items are output. When an accountant is participating in the design of a new system, a data dictionary can also be used to plan the flow of transaction data through the system.
Finally, a data dictionary can serve as an important aid when investigating or documenting internal control procedures. This is because the details about edit tests, method of file security, and similar information can be stored in the dictionary.