Function-Design is a design primarily aimed at satisfying specified Function-Requirements.

Alternative Names

Concept Number: *521
English Master: Function-Design
Synonyms, Variations & Acronyms: none


A specified Function-Design has two characteristics, which we primarily select it for:
Function-Requirement satisfaction, and
• satisfactory consequent Levels of performance and Cost Attributes


Illustration: none




Cross River:
Type: Function-Requirement.
Definition: Move people and goods from one shore to the opposite shore of a river.

Function-Design-Ideas [Version 1]: {Build a Bridge, Use a Boat, Swim Over “minimal design”, Take Route “Around” the River, Fly Over}.
Consideration of potential Design-Ideas: Function-Design-Ideas [Version 1] shows selecting on Function satisfaction: some Function-Designs, which satisfy the Function-Requirement.

Function-Design-Ideas [Version 2]: {{Build a Bridge and/or Use a Boat}, Not {Swim Over, Take Route “Around” the River or Fly Over}}.

Function-Design-Ideas [Version 2] shows further selection using knowledge of performance and Resource (Cost) Attributes: The Function-Designs that look most promising for the System.


1. The final real performance and Cost-Levels delivered is dependent on the Specific-Design chosen (for example, exactly what Specific-Design of bridge, or specific type of boat).

Functional design necessarily narrows the remaining design Scope to some degree. It can even narrow the design Scope to a set of Function-Designs without actually taking a final choice of Specific-Design (for example, Build a Bridge and/or Use a Boat – without yet saying exactly which Type). The final Design-Specification would then be left to a downstream Design-Process.

This delay might be justified by their more specialized knowledge downstream, or justified by the advantage of putting off the decision due to changed technology/market Conditions/costs, or due to an advantage of making the decision in the Context of many other System/project-wide decisions (avoiding sub-optimization).

2. Any Function-Design in its real implementation (as opposed to pure Function specification), will Impact many of our non-Function-Requirements (Performance-Requirements, Resource (Cost) Requirements, Condition-Constraints or Design-Constraints). This multiple Impact is inevitable whether we like it or not. We cannot, it seems, only design for one pure Requirement dimension without having some effects on the others.

When a design is primarily specified for non-function purposes (like improving a Product-Value Level), it might inadvertently Impact existing Functionality as a Side-Effect. This might possibly be acceptable. It might introduce new Function, modify old Function, or make existing Function inaccessible totally or practically.

3. The key reasons for considering Function-Design, as a distinct design Type, is that:
• you can narrow the Function-Design Scope gradually
• you become more conscious of the Side-Effects on performance and Cost
• you become more conscious of the necessity of choosing Function-Design alternatives on the Basis of their Impacts on performance and Cost.
• you can separate the design rationale for the Function, from consideration of the other Attributes.








This Concept entered by Peter Davies.

Created by system. Last Modification: Thursday 11 of July, 2019 18:26:59 CEST by Admin (Kai).

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