Writing Target and
Final Specifications
translating customer words…
into
… realizable engineering specifications
Rationale for Specs
• Need to know when you’re done.
• Need to know what is ‘good’.
• Agree on target specs before design
development begins.
• Refine and validate final specs before
detail design begins.
• Use specs to prevent scope creep!
Process for Target Specs
1. Create a list of customer needs.
(by-product of client interview)
2. Prioritize customer needs (by importance).
3. Prepare a needs-metrics matrix.
4. Compile a benchmarking chart.
5. Establish ideal as well as marginally
acceptable values.
6. Set appropriate target values.
Tips on Customer Needs
• Use interviews, observations, and
experiential information (based on
client visit/interview)
• Asses functional performance, human
factors, physical requirements,
reliability, life-cycle concerns, resource
concerns, fabrication requirements
(based on project learning)
• Play these back to your client for
their comment/clarification/approval!
Process for Target Specs
1. Create a list of customer needs.
(by-product of client interview)
2. Prioritize customer needs (by importance).
3. Prepare a needs-metrics matrix.
4. Compile a benchmarking chart.
5. Establish ideal as well as marginally
acceptable values.
6. Set appropriate target values.
Tips on Selecting Metrics
•
•
•
Ideally each customer need would correspond to a
single metric, and the value of that metric would
correlate perfectly with meeting that need. In
practice, several metrics may be necessary.
Metrics should be dependent, not independent,
variables. Specs indicate what the product must
do, but not how the specs will be achieved.
Show a table of metrics at the Oct 14 Snapshot.
Tips on Selecting Metrics
•
•
•
Metrics should be practical (ie measured with
available equipment).
Some needs cannot easily be translated into
quantifiable metrics. Indicate these by ‘subj’,
meaning that they should be interrogated by
an expert or focus group.
Metrics should include popular criteria for
comparison in the marketplace. Seek out
metrics cited in trade magazines/catalogs.
Process for Target Specs
1. Create a list of customer needs.
(by-product of client interview)
2. Prioritize customer needs (by importance).
3. Prepare a needs-metrics matrix.
4. Compile a benchmarking chart.
5. Establish ideal as well as marginally
acceptable values.
6. Set appropriate target values.
Tips on Selecting Target
Values
5 ways to express target values…
- At least X
- At most X
- Between X and Y
- Exactly X
- A set of discrete values
Validate metrics and target values in your
conceptual design review and again in your
detail design review!
Process for Final Specs
1. Develop technical models of the product.
2. Develop a cost model of the product.
3. Refine target specifications, making well
documented trade-offs as necessary.
4. Flow down specifications for overall system
into sub-systems.
5. Set appropriate values for final specs.
Summary
• Specifications are typically established
at least twice. Immediately after
identifying the customer needs, the
team sets target specifications. After
concept selection and testing, the team
develops final specifications.
• Final specifications are developed by
thoroughly assessing actual technological constraints and production costs.
They should be based on rigorous
analytical and physical modeling.
Helpful References
Ulrich and Eppinger, Product Design and
Development, 5th Edition, McGraw Hill, 2012.
Hatley and Pirbhai, Strategies for Real-Time
System Specification, Dorset House, 1998.
Rechtin and Maier, The Art of Systems
Architecting, 2nd Edition, CRC Press, 2000.