What are the best practices for writing functional specifications in real-time systems?

2 Use a standard format

For consistency, clarity, and readability, you should use a standard format when writing functional specifications. This will help to organize the information, communicate the requirements, and facilitate review and verification of the specifications. A template or guideline with a common structure can be used, such as an introduction providing an overview of the system or component, its objectives, scope, and context. Functional requirements should specify the functions that the system or component must perform, and how they relate to inputs, outputs, and events. Non-functional requirements should outline quality attributes that must be met, such as reliability, availability, security, usability, and maintainability. Interface requirements should detail any interfaces that must be provided or used, such as hardware, software, user, and external interfaces. Additionally, design constraints should indicate any limitations or restrictions that must be adhered to like standards, regulations, protocols or resources.

3 Use clear and precise language

When writing functional specifications, you should use clear and precise language that avoids ambiguity, vagueness, and jargon. You should also use consistent terminology and notation throughout the document. You should avoid using words or phrases that imply uncertainty, such as "may", "should", "could", or "as appropriate". Instead, you should use words or phrases that indicate certainty, such as "must", "will", "shall", or "is required". You should also use active voice, present tense, and imperative mood to describe the functions and the requirements of the system or the component.

4 Use diagrams and tables

To complement the textual description of the functional specifications, you can use diagrams and tables to illustrate the structure, behavior, and interactions of the system or component. Visualizing and simplifying complex concepts can be done through diagrams and tables to show relationships and dependencies among elements, as well as highlight critical aspects and exceptions. Different types of diagrams and tables can be used such as flowcharts, state diagrams, use case diagrams, data flow diagrams, entity-relationship diagrams, and tables. Flowcharts demonstrate the sequence of actions and decisions a system or component performs in response to an event or condition. State diagrams show states and transitions a system or component undergoes during operation. Use case diagrams illustrate actors and scenarios a system or component supports or participates in. Data flow diagrams indicate sources, destinations, processes, and data flows a system or component involves or generates. Entity-relationship diagrams demonstrate entities, attributes, and relationships a system or component manages or manipulates. Finally, tables display data, parameters, values, and rules a system or component uses or applies.

5 Validate and verify the specifications

After writing the functional specifications, it is important to validate and verify them to ensure they are complete, consistent, correct, and testable. They should also meet the expectations and needs of stakeholders and comply with system or component standards and constraints. Different methods and techniques can be used to validate and verify the specifications, such as reviews, inspections, walkthroughs, prototypes, and tests. Writing functional specifications for real-time systems may be difficult but following these best practices can lead to higher quality and more usable specifications that can improve the system or component.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?