Example #1 for What vs How
Music sheet is not music. It is description of music. This is the 'What' or Logical Design.
Music is played using musical instruments. This is the 'How' or the Physical Design. There are many physical designs for a given logical design.
Example #2 for What vs How
John Lennon wrote the song Come Together. This is the 'What'. The examples of 'How' in this case are the performances of :
- Michael Jackson
to the same song Come Together.
Separate Logical Design from Physical Design
How do you separate What from How in our code? Chris Stevenson's TestDox style expresses the subject in the code as part of a sentence.
- A Sheep eats grass
- A Sheep bleats when frightened
- A Sheep produces delicious milk
- A Sheep moves away from sheep dogs
This can be automatically converted to specifications in code :
describe Sheep do
it 'eats grass'
it 'bleats when frightened'
it 'produces delicious milk'
it 'moves away from sheep dogs'
When you think about the system from outside-in fashion you focus on intent. You focus on what you are doing rather than the implementation which is the 'how'.
1. Test Driven Development: Ten Years Later by Michael Feathers and Steve Freeman on
Search YouTube and watch the videos for Come Together performed by The Beatles, Michael Jackson, Aerosmith and Elton John