1. Pattern-Oriented Cluster: Comp 630/650/655
About patterns
Outline
What’s a pattern?
An example from fast food
Comments on the “definition”
Patterns and software development culture
Pattern definition exercises
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

2. Pattern-Oriented Cluster: Comp 630/650/655
What’s a pattern?
Alexander’s characterization
(quoted by Fowler)
Recurring problem
Environment in which it occurs
Core of a solution
Has been used successfully multiple times
Can be used many times without ever doing it the same way twice
Christopher Alexander wrote about patterns in building architecture
His ideas have proved very popular among software developers
Like all good ideas, the building architecture/software architecture analogy has been taken too far
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

3. Example: fast food pattern
Problem: people getting burned on hot drinks
Environment: fast food restaurants
Solution: print warnings on packaging
Name: Achtung - Heiss
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

4. Pattern-Oriented Cluster: Comp 630/650/655
Other solutions
Solution: make in advance, heat to safe temperature when serving
Name: Heat-n-Serve
Solution: make drinks at safe temperatures
Name: Low-Temperature Recipe
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

5. What’s the real problem?
Heat-n-Serve and Low-Temperature Recipe are about preventing burns
Achtung-Heiss is about preventing lawsuits
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

6. Definition vs Characterization
Definition: Duck
Any of numerous relatively small and short-necked web-footed swimming birds of the family Anatidae.
Characterization: Duck
Walk: waddle
Sound: quack
Patterns characterize more than they define
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

7. Comments on the characterization
Patterns have consequences
Some patterns go together
Class Table Inheritance (285) usually implies Domain Model (116)
Using a pattern can introduce other problems
Developers often have trouble getting comfortable with Domain Model (116)
Architecture patterns differ from GOF
It’s all Indirection …
GOF (Gang of Four == Gamma, Helm, Johnson, Vlissides) are OO Design patterns that (mostly) address recurring problems of implementing architecture patterns such as Fowler’s Domain Model (116)
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

8. Patterns and software culture
At best: gray heads use patterns to help younger people without being dogmatic
At worst: pattern writers kill lots of trees
At best: patterns make communication more efficient
Huffman codes for architecture/design descriptions
Can save effort in project design documentation
At worst: patterns add confusion
People may have different understandings of a pattern
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

9. More on patterns and culture
Naming patterns is
Really important
Really hard
Patterns are owned by the community
Nobody invents patterns
You can’t patent a pattern
Patterns are “identified” or “discovered”
Pattern writers depend on feedback
Especially about naming, applicability, consequences
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655

10. Pattern-Oriented Cluster: Comp 630/650/655
One more comment …
The analogy between building architecture and software architecture
Can be helpful
Can be over-used
12/1/2018
Pattern-Oriented Cluster: Comp 630/650/655