Design Criteria

What

Design Criteria.

How

The dish

Design Criteria Check List

Ingredients

• Rich Picture
• Storytelling
• Exact Requirements (Timing, etc.)
• Class Diagram and a short descriptions
• State Machine Diagrams
• Use Cases
• Sequence Diagrams expressing the dynamics of the system
• Results from Functions Analysis
• Results from User Interface Analysis
• Results from System Interface Analysis

Process

Make a list of criteria which the product must comply with. Use a check list (See below).

How - in details.

The price of the product.

Consider how much the product must cost. This includes sales price, development cost, HW cost, etc.

Development time.

Consider the time it must take to develop the system-to-be.

When can the production start? When can the sale start?

Performance.

Consider the performance of the product when it is to be used. Is it an expensive high quality product or is it a low price product which is to be sold in large quantities?. If it is a product for which a customer has paid a large amount of money, then no defects are accepted. Is the system-to-be a product which must be safe in use, optimal performance is necessary and malfunctions are not accepted. Examples could be: Electronically controlled wheelchairs, systems for use in hospitals, etc.

Another important aspect is which part of the world it is planned to sell the product-to-be. Different countries have different legislations. If you are planning to sell the system-to-be in European countries you must test your product in compliance with EU regulation and consequently mark your product with the CE certification.

Reliability and lifetime.

The reliability and lifetime must be considered. Is the system-to-be a product which must be safe to use, then it is necessary that the reliability and lifetime are high and no failures are accepted. Examples could be: Electronically controlled wheelchairs, systems for use in hospitals, etc.

Already developed parts.

If it is important to use already developed parts, these must be considered early in the project phase, because it will have an effect on the selection of the technical platform. It is not certain that these parts fit completely into the system-to-be. You have to consider how they worked in previous projects. Do they fit into the new project? Was the design as wished or did some parts have defects? Are they good enough or do you have to design new parts?

Service and maintenance

Consider service and maintenance. No matter how well- developed the system-to-be is, it will sometimes fail or must be maintained. Maintenance can be different sorts of adjustments of the system-to-be. Sometimes replacing old HW or changing SW.

Type of System.

Consider which type of system is wanted.

It is possible to design systems containing much or little electronics. The more electronics the more features are normally possible. The choice could be a system that contains no electronics at all. It is, for instance, possible to construct a heating installation with no electronics and where the parts used are purely mechanical featuring only a few adjustment possibilities. It is also possible to construct a heating installation containing much electronics. In this case there are many adjustment possibilities, and it will be easy to guide the user.

Why

It is important to consider the design criteria in order to market the product in the right way. Failure to do so may result in a product which does not have the right specifications in relation to the consumer. This might reduce the sale. These criteria also have major impact on the choice of the technical platform.

Example

Design Criteria for the heating installation:

    Issue         Critical       Very Important    Important   Less Important  Notes

Performance                           X                                          1
Usage                X                                                           2
Reliability          X                                                           3
Easy serviceable                                       X                         4
Remote maintenance                    X                                          5
Cost effective                                         X                         6

Notes:

1. The performance is very important.

2. There must not be any difficulties using the system. All kinds of people must be able to use it, there must not be special training! The system-to-be must contain enough electronics to ease and secure the use. It is also preferable to have the possibility to collect different kinds of data from the system-to-be.

3. Errors must not occur. It will be critical if an error shuts down the heating of the house. If the temperature outside is below zero, the house and the system can be damaged if it is not heated. Therefore, the reliability must be high!

4. The system must be easy to repair, if errors occur.

5. All maintenance must be easy, with no or a minimum of disturbances for the user.

6. Many of the parts in the system may already have been developed by other companies. It must be considered how the lowest price is obtained. For all parts of the system-to-be it must be a choice between developing the different parts or buy something similar and redesign if necessary.

Used In

The Design Criteria is used as background information in the rest of the development process and must be obeyed.

Subsystem Architecture Design is the next natural step to go to.