Requirements Document

A requirements document, also known as a Software Requirements Specification (SRS), is a formal description of a system to be developed. It sets out the expected behavior of the system in detail and serves as a contract between the client and the software developers.

A requirements document includes both functional and non-functional requirements.

Functional Requirements: These are the features and operations of the system. They define what a system is supposed to accomplish. For example, in a banking software system, a functional requirement might be that the system is able to process withdrawals and deposits.
Non-functional Requirements: These refer to the performance and usability of a system. They define how a system is supposed to be. For example, in the same banking system, a non-functional requirement might be that the system should be able to handle 10,000 simultaneous users, or that it should have a response time of no more than 2 seconds.

In addition to the above, a requirements document often includes other important information such as:

System Overview: A brief description of the system, its purpose, and its audience or users.
System Features: A detailed description of the system's features and functionalities.
Interfaces: Description of the user, hardware, and software interfaces.
Constraints and Assumptions: Any limitations, constraints, or assumptions associated with the system.
Use Cases: Specific scenarios of how users will interact with the system.

The requirements document plays a critical role in the software development process. It helps ensure that the developers and the clients have a clear understanding of what the software should do. It also provides a basis for estimating costs and schedules, and a reference for validation and verification of the final product. It's typically written by a systems analyst or a business analyst, often in collaboration with the system's future users.

Below is an example of a simplified software requirements document. This example is for a hypothetical Mobile Banking Application.

Mobile Banking Application - Software Requirements Specification

1. Introduction

1.1 Purpose

The purpose of this document is to present a detailed description of the Mobile Banking Application. It will explain the purpose and features of the system, the interfaces of the system, what the system will do and the constraints under which it must operate.

1.2 Scope

The Mobile Banking Application enables bank customers to handle their banking transactions from their mobile devices. It provides features such as balance checking, fund transfers, bill payments, and account management.

2. General Description

2.1 Product Perspective

The Mobile Banking Application will serve as an addition to the bank's current online banking system, providing an intuitive and convenient mobile platform for banking transactions.

2.2 User Classes and Characteristics

Regular Customers: These users will use the application to perform daily banking transactions.
Bank Admin: This user will have administrative access to the backend of the application.

3. System Features

3.1 Check Account Balance

Users can view their account balances.

3.2 Fund Transfer

Users can transfer funds from their accounts to other accounts.

3.3 Bill Payment

Users can pay their bills directly from their account through the application.

3.4 Account Management

Users can manage their personal information, change their passwords, and view their account transaction history.

4. External Interface Requirements

4.1 User Interface

The application will have an easy-to-use, intuitive graphical interface suitable for mobile devices.

4.2 Hardware Interface

The application will communicate with the bank's central server for data retrieval and transaction handling.

5. Non-functional Requirements

5.1 Performance Requirements

The application should be able to support multiple users simultaneously without performance degradation.

5.2 Security Requirements

The application will use encryption and secure protocols to protect sensitive information. User authentication will be required.

5.3 Availability

The application should be available for use 24/7, barring maintenance periods.

6. System Constraints

The Mobile Banking Application will need to operate within the following constraints:

Compatibility: The application must be compatible with iOS and Android devices.
Regulation: The application must comply with all relevant banking and privacy regulations.

This is a very simplified requirements document, and real-world versions would be far more detailed. It would include detailed specifications for each feature, specific interface requirements, and perhaps even some initial design or wireframe sketches. It would also include more detailed descriptions of the expected user base, use cases, and any assumptions or dependencies that the project has.