A System Requirements Specification (SRS) is the formal engineering document that captures all functional and non-functional requirements a system must satisfy. It is derived from stakeholder needs (market requirements, customer feedback, regulatory mandates) and represents the binding contract between what is needed and what will be built. The SRS drives all subsequent design, verification, and validation activities.
A well-structured SRS includes: purpose and scope, system overview, stakeholder needs, functional requirements (organized by system function or operational mode), non-functional requirements (performance, reliability, safety, environmental), interface requirements (hardware, software, human), and design constraints. Each requirement has a unique identifier, enabling traceability through the requirements traceability matrix.
IEEE 29148-2018 is the governing standard for requirements engineering, providing templates and criteria for well-formed requirements. Common SRS failure modes include: requirements that are ambiguous or subjective, conflicting requirements between subsystems, requirements missing measurable acceptance criteria, and requirements that change scope without version control. A baselined SRS with a formal change process prevents scope creep and provides an audit trail for design decisions.
Practical Example
An SRS for an autonomous inspection drone includes: system description, operational concept, 47 functional requirements across navigation, sensing, and communication subsystems, 23 non-functional requirements covering weight, battery life, operating temperature, IP rating, and regulatory compliance (FAA Part 107).
How SpecZero handles this
SpecZero's Requirements section serves as a lightweight SRS, capturing essential requirements with target specifications in a structured lane-based format. While not a formal SRS document, it provides the traceability backbone that links requirements to design concepts and ultimately to BOM items.
Related terms
Functional Requirements
Statements of what a system must do — behaviors, inputs, outputs, and capabilities.
Non-Functional Requirements(NFR)
Requirements that define quality attributes — how well a system performs, rather than what it does.
Requirements Traceability Matrix(RTM)
A document that links requirements to their sources, design elements, and verification tests.
IEEE 29148
The IEEE standard for requirements engineering, defining processes and criteria for well-formed requirements.