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Specification and Requirements
Inc Systems Engineering

Essential Product Development for Engineers

Specification and Requirements

To develop any product, those involved require clear instructions and direction if they are to design and manufacture something that is fit for purpose. The problem for small manufacturers is there are a range of terms, sometimes used interchangeably, that set out what is expected at the start of a development project. Examples include Specification,  Design Brief, Requirements and Synopsis. This can sometimes be confusing. This section aims to clarify some of these terms.

To guide your development project to success, what you need is clearly laid out information in the form of a plan, listing the key considerations. Additionally, it is worth noting, like so many aspects of product development, this information is scalable. For simple products with a few components, a shorter relatively straightforward document will do. For more complicated assemblies or systems, detailed information will be needed to guide and instruct development activities.

Design Brief

The Design Brief is set at quite a high level, rather than concentrating on the detail. It focuses on the broad aims, whilst listing only key constraints and considerations. The Design Brief focuses on results and outcomes of the development – what you want to achieve from a big picture point of view.

The Design Brief should include a short statement, describing in a succinct way what the purpose of the product is and what benefits it aims to offer. The key advantages for the target customer should be articulated. The product should fulfil a specific need or a list of needs. These should be clearly identified.

In short, what problem are you trying to solve? It is worth saying something about the context of the product, for example where does it fit in your product range? What is the trigger for the development project (for example technology, market opportunity, targeting a new market or customer demand)? Also, what is the overall business context and purpose? Is it a new revenue stream, business growth, new market entry etc?

Additionally, include some of the big constraints on the project such as budget, lead-time, broad quality considerations and manufacturing issues. Design Briefs are routinely used in product design contexts, between designers and their clients.


The Specification sets out a list of requirements necessary to successfully guide the development process and deliver a product that is fit for purpose. Specifications may list different types of requirements, such as performance and user requirements. Cost, quality and lead-time are common requirements.

The details contained in the specification assist engineers at each stage of the product development process and should be agreed by the customer and supplier (this may be between businesses or internally within an organisation). Specifications are often derived from the design brief, providing greater levels of detail necessary to kick-start design work.

Specifications can potentially form part of a contractual agreement between suppliers and customers. Specifications, like other technical documents, are scalable; detailed specifications for complicated products and more straightforward specifications for simpler assemblies. Specifications may include references to standards, which themselves may be international, national, industry or business-specific.

A well written specification should be clear, containing only essential helpful information. Keeping the specification succinct also helps minimise development activities and therefore lead-time and costs. The opposite is also true, therefore should be avoided. Instead the specification should only list what is required to get the job done, yet at the same time it should be achievable and not encourage more development than is necessary.

The specification document concisely sets out the problem to be solved, together with any constraints. This enables potential solutions to be developed to meet the overall objective. Listed specification requirements can be ranked in priority order, as well as separated as essential and desirable. Because all other stages of product development refer to or are driven by the specification, the importance of ensuring it is accurate and correct, cannot be underestimated.

Writing a Product Design Specification  

Useful Ideas for Product Design Specification 

Systems Engineering

Requirements are typically listed within a specification. Requirements play a fundamental role within Systems Engineering; an interdisciplinary approach often used to develop more complex engineering projects.

Systems Engineering initially focusses on capturing and analysing customer requirements. Once requirements are understood, system ‘functions’ can then be developed.  Initially, systems functions are defined at a high level, addressing broad aims of the system or product. Functions are then further refined to meet the more specific needs at a lower level. Consideration is given to the interaction of these functions. Development is driven by defining technical solutions to meet these functions and their respective requirements.

To ensure the design is fit for purpose and meets the specification, two activities take place – verification and validation. Verification involves testing to ensure the requirements established at the start, are being met. Validation is undertaken by checking the processes used during development have been followed. The most common method of verification and validation is testing. However others involve analysis, modelling, inspection and review. Thorough documentation of requirements and processes is required for detailed verification and validation to be effective.

Specification and Requirements

Systems Engineering Overview 

Combat Product Complexity with Systems Engineering - Part 2 from PTC
Complex System Engineering from Emmanuel Fuchs

Next... Concept Design: Successfully Sourcing and Generating Ideas

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