Requirements Engineering: Functional vs. Non-Functional Requirements
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Understanding Functional Requirements
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Hello everyone! Today we will discuss functional requirements and their critical role in designing embedded systems. Can anyone tell me what they think functional requirements are?
I believe functional requirements are what the system is supposed to do, like tasks or functions it must perform.
Exactly! Functional requirements detail the specific services or behaviors a system must provide. For example, 'The system shall activate the motor when the temperature exceeds 80 degrees Celsius.' It directly specifies actions.
So, they are specific tasks that the system has to perform based on certain conditions?
Correct! This specificity helps developers understand what to build. Can anyone think of another example of a functional requirement?
How about 'The system shall display the battery level on the LCD screen'?
Great example! It clearly demonstrates what the system needs to accomplish. Remember, functional requirements are essential because they lay the foundation for how the system interacts with users and other systems.
In summary, functional requirements specify what a system does, acting as a checklist for functionalities.
Diving into Non-Functional Requirements
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Now, let's shift our focus to non-functional requirements. Who can summarize what these refer to?
They define how well the system performs its functions, right? Like speed or security?
That's right! Non-functional requirements describe the quality attributes of the system, such as performance, reliability, and usability. An example would be, 'The control loop shall execute with a period of 1 millisecond Β± 10 microseconds.'
So, itβs less about what the system does and more about how it does it?
Precisely! While functional requirements focus on specific functionalities, non-functional requirements describe the limits and standards those functionalities must adhere to. Can anyone think of a non-functional requirement related to safety?
What about 'The motor shall immediately shut down if an overcurrent condition is detected'?
Excellent example! This non-functional requirement ensures safety and quality by addressing potential hazards.
To summarize, non-functional requirements are vital for determining how a system will meet user expectations and perform under specific conditions.
The Importance of Balancing Both Types of Requirements
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So now we know what functional and non-functional requirements are. Can someone explain why it's important to balance the two?
I guess both types are needed to ensure that the system works correctly and reliably?
Exactly! Balancing both ensures that not only does the system perform the necessary functions but also meets quality attributes like safety, reliability, and usability. A system could function well but be unsecure or unreliable, which would lead to failure in real-world applications.
So if I only focused on functional requirements, I might miss crucial aspects that could affect the system's performance or safety?
That's correct! Poorly defined or neglected non-functional requirements can lead to severe issues down the line, such as security breaches or system failures.
In summary, achieving a fine balance between functional and non-functional requirements is essential for the success and reliability of embedded systems.
Introduction & Overview
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Quick Overview
Standard
In this section, functional requirements define what a system must perform, detailing services provided and system functions. Conversely, non-functional requirements capture quality attributes like performance and security, framing how those functions are executed, which plays a crucial role in the overall design and success of embedded systems.
Detailed
Requirements Engineering: Functional vs. Non-Functional Requirements
In the field of embedded systems design, requirements engineering is crucial for establishing the system's purpose and constraints. This section differentiates between functional requirements, which specify what a system should do, and non-functional requirements, which describe how the system performs those functions.
Functional Requirements
Functional requirements define specific functionality or behaviors that the system must provide, directly linked to the system's features and services. Examples include tasks that the system must execute under certain conditions, such as The system shall transmit sensor data every 100 milliseconds. These requirements are typically actionable, providing a clear understanding of expected outputs based on inputs.
Non-Functional Requirements
In contrast, non-functional requirements focus on quality attributes of the system. These attributes can include performance metrics (like execution speed), reliability factors (such as fault tolerance), security stipulations, usability needs, and constraints related to environmental factors. An example here might be The system shall operate continuously for 5 years without failure. These requirements are vital for ensuring that the system meets broader expectations beyond function and are often harder to quantify and evaluate during implementation.
Understanding the balance and interplay between functional and non-functional requirements leads to comprehensive systems engineering, enabling more reliable, efficient, and secure embedded systems.
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The Critical Role of Requirements Engineering
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Chapter Content
8.5.1 The Critical Role of Requirements Engineering
- Definition: Requirements engineering is the systematic process of eliciting, documenting, analyzing, validating, and managing system requirements throughout the development lifecycle. It's the crucial first step that defines the problem to be solved.
- Why it's Crucial for Embedded Systems:
- High Stakes: Errors in requirements can lead to catastrophic failures in safety-critical embedded systems.
- Hardware/Software Interdependence: Requirements often span both hardware and software, demanding careful coordination.
- Real-Time Constraints: Unique timing, performance, and power requirements must be precisely captured.
- Early Problem Detection: Misunderstood or incomplete requirements are the root cause of many project failures. Identifying them early saves immense time and cost.
Detailed Explanation
Requirements engineering is the process through which we gather, document, and manage the requirements of a system before its actual development begins. This process is vital in embedded systemsβlike those controlling medical devices or automotive systemsβwhere errors can lead to serious issues. For instance, a miscommunication about how quickly a device should respond could lead to dangerous performance failures.
Examples & Analogies
Think of requirements engineering like a blueprint for a house. If the architect doesn't capture the homeowner's specifications correctly, the house won't meet the owner's needsβleading to expensive and sometimes dangerous changes after construction has begun.
Types of Requirements: Functional vs. Non-Functional
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Chapter Content
8.5.2 Types of Requirements: Functional vs. Non-Functional
- A. Functional Requirements:
- Definition: These define what the system must do or what functions it must perform. They describe the services the system should provide to its users or to other systems.
- Characteristics: Typically expressed as actions, behaviors, or data transformations.
- Examples in Embedded Systems:
- "The system shall activate the motor when the temperature exceeds 80 degrees Celsius."
- "The system shall transmit sensor data via SPI every 100 milliseconds."
- B. Non-Functional Requirements (Quality Attributes):
- Definition: These define how well the system performs its functions or what qualities it must possess. They specify constraints on the system's operation, development, or environment.
- Categories and Examples in Embedded Systems:
- Performance: "The system shall respond to a critical alarm within 50 microseconds."
- Safety: "The motor shall immediately shut down if an overcurrent condition is detected."
Detailed Explanation
Requirements in embedded systems typically fall into two categories: functional and non-functional. Functional requirements specify what the system is supposed to do, such as activating a motor or sending data. Non-functional requirements outline how well those functions must be performedβsuch as response time, reliability, safety, and usability. This distinction is critical because while functional requirements inform the capabilities of the system, non-functional ones ensure it meets quality expectations.
Examples & Analogies
Consider a smartphone as an analogy. A functional requirement might specify that the phone has a camera that takes photos. A non-functional requirement could state that the camera must take a photo in less than 1 second under various lighting conditions. Without both, a great camera could be rendered useless if it takes too long to snap a picture!
Common Specification Techniques
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8.5.3 Common Specification Techniques
Once requirements are elicited, they need to be documented clearly and unambiguously.
- A. Natural Language Specification (Plain Text):
- Concept: Requirements are written using ordinary human language (e.g., English).
- Advantages: Easy to understand for all stakeholders.
- Disadvantages: Prone to ambiguity, incompleteness, inconsistency.
- B. Structured English (Pseudo-code like):
- Concept: Uses a limited and defined subset of natural language.
- Example:
IF Sensor_Reading > Threshold THEN
Start_Motor
ELSE IF Motor_Running THEN
Stop_Motor
END IF
- C. Data Flow Diagrams (DFDs):
- Advantages: Excellent for visualizing data relationships.
- Disadvantages: Does not show timing or control flow.
- D. Formal Specification Languages:
- Advantages: Eliminates ambiguity but requires specialized skills.
Detailed Explanation
After defining requirements, clear documentation is necessary to ensure a common understanding among all stakeholders. Common techniques include natural language specifications for straightforward communication, structured English for more technical clarity, data flow diagrams for visualizing data processing relationships, and formal specification languages for rigorous mathematical representation. These techniques each have their strengths and weaknesses, influencing how requirements are transformed into actionable insights.
Examples & Analogies
Documenting requirements can be likened to planning a trip. Natural language would be like telling friends, 'We should go to the mountains.' Structured English could outline 'If it's sunny, drive; if it rains, take the train.' A data flow diagram would illustrate the itinerary visually, and formal specifications might resemble a legal document detailing all conditions for the trip!
Key Concepts
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Functional Requirements: Specify what the system must do.
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Non-Functional Requirements: Outline how well the system performs its functionalities.
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Requirements Engineering: The systematic process of managing requirements throughout the lifecycle.
Examples & Applications
An embedded system must activate an alarm when smoke is detected.
The system shall encrypt all user data before storage.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
Functional tasks are what we do, Non-functional tells how well, it's true!
Stories
Picture a restaurant where the chef (functional requirement) prepares dishes. The critics (non-functional requirements) evaluate the food on taste, presentation, and service. Both are needed for a successful dining experience.
Memory Tools
F.U.N. - Functional, Usable, Necessary! These are core aspects of functional requirements.
Acronyms
R.E.F.N. - Requirements Evaluate Functional Needs. This can help you remember the primary focus of requirements engineering.
Flash Cards
Glossary
- Functional Requirements
Specifications that define what a system must do or the functions it must perform.
- NonFunctional Requirements
Quality attributes that define how well a system performs its functions, including constraints on performance, reliability, and security.
- Requirements Engineering
The process of eliciting, documenting, analyzing, validating, and managing system requirements throughout the development lifecycle.
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