010 Specifications, Requirements, Functions and Features

There is a multitude of different ways and practices to describe specifications. Please consider the lecture on this portion for more details. To summarize there are three major types of terminologies which needs consideration

System Specification / Target Specification / Functional-Specifications / Product Specification (Deutsch: "Pflichtenheft")

The system specifications are usually defined by the customer. They are the most relevant basis for a design and need to be fullfilled by the development. Any deviation from this system-specification needs clarification. In a business-context, any deviation will become cost-relevant.

The system specifications usually go along with certain features of the product. Especially when it comes to complex software functionality, the number of features may be thousands of each feature will be tracked as an indicidual specification

Requirement-Specifications / Performance-Specifications or just Specifications (Deutsch: "Lastenheft")

The requirements-specification describe the internal development target for a product. They are usually much more detailed and updated frequently during the development. When the development is progressing the device is going to be splitted in functions. With each function the requirements specifications continue to grow and will get independent subsections for the functions.

Company Standards and Norms (ISO/DIN)

Comparable to product-specifications they can be considered a source for requirements. Usually the product-specification requires some ISO/DIN norms to be used (e.g. norms on product development) and this then triggers some internals standards/processes to be considered. So company-standards usually do not stand for themselves, as they are otherwise not really adding value to the product development. At least they take influence on cost of development/production/overhead of the task, so a n internal company-standard should help to minimize across all products the cost-structure of the company.

Examples

Product Specification Version 1.0

(make sure to keep versioning when you do those lists)

Index	Titel	Value	Unit	Importance*	Source	Links to Req. Specification	Comment
AA	Weight	<1	kg	R	Customer Mechanics	1
AB	Power consumption	<1	W	R	Customer Electrical	15
AB	Power consumption	<0.5	W	O	Customer Electrical	25	Customer wants to achieve a battery usage in future generations of the device
AC	Costs	<100	EUR	R	Customer Purchasing	2,3
...

* there are hundreds of ways how to handle the "importance". The most basic information is to define Required values (R) and optional values (O). But you can also give an analogue rating like a number from 0 to 5 with 0 means "optional" and 5 means "super important".

Requirement Specification Version 1.0

(make sure to keep versioning when you do those lists)

Index	Titel	Value	Unit	Importance*	Source	Links to Source	Discipline	Influence by product function	Comment
1	Total Weight	<1	kg	R	Product Specification	AA	ME, EE	(this column can be filled only after functional decomposition)
2	Bill of Material Costs	<20	EUR	R	Product Specification	AC	ME, EE		Break-Down by target-costing team
3	Assembly Costs	<5	EUR	R	Product Specifications	AC	P		Break-Down by target-costing team
...

Areas requirements may come from

Within literature on design there are always checklists which should help to tailor the requirements and to prevent missing a specific topic or area while creating the lists. I personally like the lists of "Pahl Beitz", although they may need to be extended beyond the technical features a bit.

Areas to consider
Geometry	How large should it be, are there any limitations or boundaries. How does the geometry change when operating. Anything to consider compared to storage and non-operational states.
Kinematics	How does the mechanical interface look like. How is it fixated, should the output translate/rotate, ...
Forces	What are the in-/ and output forces or torques generated by the device but also applied to the device
Energy	Power sources available, output power, radiation relevant, other "exotic" forms of energy existing (accelerations)
Material	Any exposure to materials (chemical, biological,...). Any limitations on material choices
In- and Output Signals	What kind of control signals does the device receive, what kind of output signals should it generate?
Safety	Passive or active safety of the device relevant?
Ergonomics	Even if not required, considering the ergonomics of usage will greatly improve the perception of quality of your work!
Manufacturability	Can all parts be manufactured or are available of-shelves? Ask for help if you are unsure!
Assembly	Can it be assembled and how is the assembly-sequence?
Control	Any need for open- or closed-loop control? Reaction timings, dynamics of this?
Mounting	if part of a larger assembly
Transport	Does it has to be moved, if so, mounting points, size to fit through a door, weight
Noise	Rattle/squeek/mechanical play/operational noises of relevance?
Repair	Does it need to be repaired, in which areas, and how to access later
Costs	Prototype costs, series costs
Timing	Major milestones for the development and the delivery
Quantity	What quantity of the device needs to be built in which time - will greatly influence the emphasis and balance between manufacturability/assembly vs. all other features