1. A set of information describing the contents, format, and structure of a database and the relationship between its elements, used to control access to and manipulation of the database.
  • It is a set of all the elements composing or included in a set of data flow diagrams describing a system.
  • Data dictionary stores:-
                           1.  Details and description of dataflow.
                           2.  Datastores
                           3.  Processes   
 
  • The data dictionary is a structured repository of data about data.
  • It contains description and definition concerning the data element, data structure, interrelationships, and other characteristics of a system.
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  • It is a list of the element included in a set of data flow diagrams describing a system.
  • It is an integrated part of the system specifications.
  • Without a data dictionary, DFD's just pictures with no details.
  • A data dictionary is developed during the data flow analysis.

NEED FOR A DATA DICTIONARY:- 

  • To manage the details in a large system.
  • To document the features of the system.
  • To identify, clarify, and define system requirements.
  • To search for a data item.
  • To evaluate the characteristics of the system.
  • To locate errors in the system.
  • To build the database and design the software.
  • To record the details of each element and data structure.


COMPONENTS OF A DATA DICTIONARY:-


1.  Data element

 The data element is the smallest unit of data that has some meaning. It cannot be decomposed further. Data elements are also called the data item, elementary item, or just field. 
 The data element entry consists of the following item:-
  • Data Name:- Unique names are given to data items. Each element is referred by its name in the entire system. The name should be a meaningful one. A  common standard specifies that data names should not be more than 30 characters and the character set is A through Z, number 0 through 9, and hyphen.
  • Data description:- It is a brief description of what the data element represents. Data description should be written assuming that the person does not know about the system.
  • Aliases:- Aliases are synonyms or other names for the element. For example, an Invoice may be called Statement, Bill, or Price.
  • Length:- Length identification of the number of spaces the is required for each data item. It is needed later during the system development process.
  • Data values:- In some processes only specific data values are permissible.

2.  Data structure


A data structure is a set of data items that are related to one another.
The data structure is used to define or describe the system components. Both data flow and data stores are data structures. Data structures are built on four relationships of components which may be data elements or other data structures. 



ADVANTAGE OF DATA DICTIONARY:-

  • It is used to locate errors in the system descriptions.
  • It is a valuable reference for coming up with the system.
  • It expedited analysis in decisive additions & modifications within the system.
  • It is accustomed to finding errors within the system descriptions.
  • It helps the analyst to record the small print of every part and organization.
  • It helps in human action meanings of various parts, terms & procedures.      

DISADVANTAGES OF THE DICTIONARY:-

  • A data dictionary is a very time-consuming job.
  • It is not acceptable to many non-technical users.  
  • It doesn't offer practical details.
  • Creating a brand new data dictionary could be a terribly huge task. it'll take years to make one.
  • It ought to be designed before to require all the benefits of it. Otherwise, it'll produce issues throughout its life.