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Last Updated: Mar 27, 2024
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Data Dictionaries In Software Engineering

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Prerita Agarwal
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23 Jul, 2024 @ 01:30 PM

Introduction

A data dictionary is a structured repository that contains information about the data in the system. It includes all the data flows and the contents of all stores appearing on all data flow diagrams in a data flow diagram model. 

A DFD (data flow diagram) model consists of several levels of DFDs such as level-0 DFD, level-1 DFD, level-2 DFD, etc. A single data dictionary should capture all the data appearing in all the DFDs of the DFD model. 

Each entry in the data dictionary consists of a set of details describing the data used or produced in the system. Each item is identified by the name of the data item, aliases (some other names for them), descriptions, range of all possible values, Data Structure definition. The dictionary is developed during data flow analysis and asserts the analysts involved in determining system requirements. 

data dictionary in software engineering

What is a data dictionary?

A data dictionary provides terminology for all relevant data to be used by the developers in a project. It helps in performing analysis based on the impact of some data on the processing activities. It also helps the developers to determine the definition of different data structures in terms of their basic elements while designing activities. 

In the case of large systems, data dictionaries may become extremely voluminous and difficult to handle. In such case, CASE (Computer-Aided Software Engineering) tools are used, that capture all the data items appearing in the DFD and automatically generate the data dictionary.

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Components of Data Dictionary

A data dictionary is a database that stores information about data, such as its meaning, relationships, and structure. The main components of a data dictionary include the following:

Data Definitions

It includes clearly and concisely describing data elements, their business meaning, and data types.

Data Relationships 

It describes how different data elements are related to each other and the nature of the relationship.

Data Constraints 

It defines rules and restrictions that govern the use of data, such as primary keys, foreign keys, and data validation rules.

Data Usage 

It describes how data is used in business processes, reports, and applications.

Data Ownership

It identifies who is responsible for maintaining and updating data.
 

All these components play a crucial role in creating a complete and accurate data dictionary that various stakeholders across an organization can use.

Data Dictionary Notations Table

x= a + b Here,” = ” represents equivalence, and + denotes composition. So this indicates, x consists of data elements a and b.
x= [a/b]  Here,” / ” may appear multiple times. So this indicates, x consists of either data element a or b.
x= a + (b)  Here, contents appearing in brackets are optional. So this indicates x consists of either a or a + b. 
{ } Here. { } represents iterative data definition. So this indicates x consists of y or more occurrences of data element a.
x = (a) z It indicates x consists of z or fewer occurrences of data element a. 
x = y(a} z It indicates that x consists of some occurrences of data clement a which are between y and z.

Example: 

{name}5 denotes five name data.

{name}* denotes zero or more instances of name data.

  •  /*---------*/ : Anything appearing between /* and */is considered as comment.

Types Of Data Dictionaries

A data dictionary is a Database that stores information about data such as its meaning, relationships, and structure. There are two main types of data dictionaries:

Business Data Dictionary

It contains information about data related to a specific business domain or application. It typically includes details such as data definitions, data types, relationships, and constraints.

Technical Data Dictionary 

It contains information about the technical aspects of data such as tables, columns, and keys in a database. It also includes details such as data storage, access, and performance.
 

Both types of data dictionaries are essential for maintaining accurate and consistent data across an organization, and they help to ensure that data is properly used and understood by different stakeholders.

Features of Data Dictionary 

  1. It is crucial to create an order list from a subset of the items list.
  2. It helps in designing test cases and designing the software.
  3. It is essential for creating an order list from a complete items list.
  4. The data dictionary is also vital for finding the specific data item object from the list.
     

Uses of Data Dictionary

1. Manage details in large systems where a huge volume of data flows through them.

2. Document features of the system such as processes and data stores, which is important for a complete understanding of the system.

3. Facilitate analysis of the details in order to evaluate characteristics and determine where system changes should be made. 

4. Locate errors and omissions in the system.

In other words, a data dictionary is a repository (manual or computed-based) containing information about the various data objects appearing on cache DFD. A data dictionary is used to provide an organized approach for representing the characteristics of each data object and control item. There are no standard formats for the data dictionary. The data store notation in a DFD shows the existence of one or more data items of stored data. 


Importance of Data Dictionary

  • Data Dictionary allows developers to use consistent terms when discussing the same data. It avoids confusion and makes teamwork smoother.
  • It helps developers by giving them a common language to describe all the data they work with.
  • The data dictionary provides clear explanations for different data types which makes it easier for everyone to understand
  • A data dictionary helps handle queries more quickly and efficiently using RDBMS(relational database management system). It is a helpful guide that assists developers in finding and working with the data they need.
     

Advantages of Data Dictionary

  • It serves as a valuable reference in any organization.
  • It improves analyst/user communication by establishing consistent definitions of various elements, terms, and procedures.
  • Since the database is huge and has lots of tables, views, constraints, indexes, etc, it won't be easy to remember. Data dictionary helps the user by providing these details.

Disadvantages of Data Dictionary

  • In the beginning, setting up the data dictionary may take time and effort.
  • Keeping the data dictionary up-to-date can be a lot of work.
  • Relying too much on the data dictionary might cause us to miss important details about the data.
  • Maintaining the data dictionary needs extra time and people.
  • If the data dictionary is not regularly updated, it could lead to mistakes and confusion.
     

Frequently Asked Questions

What are the benefits of data dictionary?

A data dictionary enhances data quality and consistency across systems by providing a centralized repository of data definitions, formats, and relationships, facilitating better communication, data governance, and understanding among stakeholders.

What are the types of data dictionary in software?

Data dictionaries in software include global, local, and distributed types. Global data dictionaries serve multiple systems, local dictionaries are system-specific, and distributed dictionaries share data across various systems.

What is the structure of a data dictionary?

A data dictionary typically contains metadata about data elements in a system. It includes information like data names, types, sizes, descriptions, relationships, and constraints, aiding data management and understanding.

What is a data dictionary used for?

A data dictionary is used to store metadata about data elements in a database or system. It aids in data management, documentation, data validation, and helps developers understand data structures.

Conclusion

In this blog, we have discussed Data Dictionary and the mathematical operators used within the data dictionary. A data dictionary is a structured repository that contains information about the data in the system. It includes all the data flows and the contents of all stores appearing on all data flow diagrams in a data flow diagram model. 

Recommended Readings:

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Happy Learning, Ninja!

Topics covered
1.
Introduction
2.
What is a data dictionary?
3.
Components of Data Dictionary
3.1.
Data Definitions
3.2.
Data Relationships 
3.3.
Data Constraints 
3.4.
Data Usage 
3.5.
Data Ownership
4.
Data Dictionary Notations Table
5.
Types Of Data Dictionaries
5.1.
Business Data Dictionary
5.2.
Technical Data Dictionary 
6.
Features of Data Dictionary 
7.
Uses of Data Dictionary
7.1.
Importance of Data Dictionary
8.
Advantages of Data Dictionary
9.
Disadvantages of Data Dictionary
10.
Frequently Asked Questions
10.1.
What are the benefits of data dictionary?
10.2.
What are the types of data dictionary in software?
10.3.
What is the structure of a data dictionary?
10.4.
What is a data dictionary used for?
11.
Conclusion