1. Writing Patterns
“The Straight Scoop”
Joseph Yoder
joe@refactory.com
www.refactory.com
www.joeyoder.com
gnisiR adniL & redoY hpesoJ 7002 thgirypoC
Writing Patterns Can Be Hard
Good Judgment comes from Experience comes from bad
Judgment….Patterns come from Experience.
Capturing and communicating (sharing) our experiences
is not easy.
While writing a pattern might not be difficult, writing
good patterns can be very difficult.
For most of us, any writing can be a difficult task. Clear
communication takes practice and iterations.
2

2. Alexander’s Pattern Definition
Each pattern describes a problem that occurs over and
over again in our environment and then describes the
core of the solution to that problem in such a way that
you can use this solution a million times over without
ever doing it the same way twice.
Alexander - building architect and author
The Timeless Way of Building
A Pattern Language
3
What is a Pattern
Quite often you hear:
” . t x e t n o c a ni m el b o r p a o t n oi t ul o s n e v o r p a si n r e t t a p A “
Alexander writes:
n oi t al e r a s e s s e r p x e h ci h w , el u r t r a p - e e r h t a si n r e t t a p h c a E “
” . n oi t ul o s a d n a , m el b o r p a , t x e t n o c ni a t r e c a n e e w t e b
Are these definitions the same?
4

3. 6
Help to construct new systems
Help to comprehend existing systems
experience of the experts
Tell a good story which captures the
Be prescriptive about the solution
solving problem
Provide Facts (ref manual) about
A Patterns Should
5
snrettap rehto ni secrof eht
fo tnednepedni era taht secrof gnitcaretni fo tes esned a evah dluohs tI
)nrettap a gnitirw fo daetsni taht od ,nac ti fi(
detamotua ro dezilamrof eb tonnac tI
eciwt emas eht gnieb reve tuohtiw semit noillim a detnemelpmi eb
nac dna ,revlos melborp eht fo thgisni eht no dliub dluohs noitulos ehT
)eluR s’nnamhcsuB( flesruoy tnevni t’ndid uoy gnihtemos eb tsum tI
efil fo ytilauq ro trofmoc namuh ot etubirtnoc tsum tI
)3 fo seluR( noitulos nevorp ,erutam a eb tsum tI
melborp eht evlos ot woh
,od ot tahw revlos melborp eht llet ot elba eb tsum uoY
txetnoc a ni melborp a ot noitulos a eb tsum tI
What is a Pattern

4. What is not a Pattern
Just a simple solution to a problem in a context
• A simple rule
• A prescriptive recipe
• An algorithm
• A data structure
7
How do Experts help decide
what makes good patterns?
Focus on Practicability
Disregard of originality
Non-Anonymous Review
Writer’s Workshop
Careful Editing
Buschmann et. al. in Pattern-Oriented
Software Architecture
8

5. Parts of a Pattern (Alexander)
Problem - when to use the pattern
Solution - what to do to solve problem
Context - when to consider the pattern
Forces - pattern is a balance of forces
Consequences, positive and negative
Examples:
Teach both problem and solution
Are the best teacher
Are proof of pattern-hood
Small Meeting Rooms

6. Small Meeting Rooms
11
e c a p S r o o d n I f o e p a h S e h T , t h gi L f o sl o o P , s ri a h C
t n e r e f fi D , el c ri C g ni t ti S , m o o R y r e v E f o s e di S o w T n o t h gi L : e e S
. s e c al p k r o w e h t g n o m a d e r e t t a c s yl n e v e , g ni dli u b
e h t f o s t r a p cil b u p t s o m e h t ni m e h t e t a c o L . s s el r o el p o e p
2 1 r o f - - ll a m s yll a e r s m o o r g ni t e e m ll a f o % 0 7 t s a el t a e k a M
. kl a t r e v e n o h w el p o e p 6 e r a e r e h t , 4 2 f o p u o r g
a n I . s kl a t r e v e n n o s r e p e n o , 2 1 f o p u o r g a n I . ] e zi s p u o r g
h ti w [ yl di p a r y r e v s b mil c kl a t r e v e n o h w r e b m u n e h t t a h t r a el c
si ti t u b ; e zi s p u o r g r o f dl o h s e r h t l a r u t a n yl r al u ci t r a p o n si e r e h T
. s s e r p x e o t el b a n e e b t o n e v a h y e h t h ci h w s a e di e v a h
y e h t l e e f o h w r e b m u n e h t d n a , kl a t r e v e n o h w r e b m u n e h t h t o b
s e c n e ul f ni p u o r g a ni el p o e p f o r e b m u n e h t t a h t n w o h s n e e b s a h t I
. sll a h e r u t c el d n a s m o o r g ni t e e m
e g r al o t ni n oi t n e t t a d n a y e n o m ri e h t t u p n e t f o s n oi t u ti t s ni
t u B . m e h t f o t u o t e g el p o e p s s el e h t , e r a s g ni t e e m r e g r al e h T
Small Meeting Rooms

7. Parts of a Pattern
(Gamma et. al.)
Intent - brief description of problem and solution
Also Known As
Motivation - prototypical example
Applicability - problem, forces, context
Structure/Participants/Collaborations - solution
Consequences - forces
Implementation/Sample Code - solution
Known Uses
Related Patterns
Example Pattern Form
s e s ail A , e m a N
t x et n o C
s ecr o F
m el b o r P
n oi t ul o S
) s e c n e u q e s n o C ( t x e t n o C g ni tl u s e R
el a n oi t a R
s n r e t t a P d e t al e R
ses U n won K
h ct e k S
r o ht u A
s e c n er ef e R
s el p m a x E
41

8. Pattern Example
How long should pattern sections be?
As short as possible but no shorter!
Albert Einstein and David Parnas
51
Name
Word or short phrase—the essence of the
pattern, some say noun phrase.
Naming is not trivial and very important.
Good names enhance communication—
especially when you can guess the intent
from the name.
Patterns “build” something. The name
should say what the pattern builds.
61

9. Aliases
The same pattern may exist elsewhere,
at another company, in a publication.
Experts use non-intuitive names that
recall folklore or deeper meanings.
Aliases can help novices.
An abbreviation or nickname can be
helpful for discussions.
71
Context
The setting—target user, patterns applied,
size, scope, timing, memory constraints,
anything that might invalidate the solution if
changed.
You’re an Evangelist or Dedicated
Champion who has called a meeting to
introduce a new idea. Members of the user
community are free to attend or not. You
have resources, your own personal
contribution or those of a Local Sponsor or
Corporate Angel.
81

10. Forces
Why the problem is hard.
The forces are often contradictory—create
tension:
You want to make your customers happy.
You have limited resources.
There’s always more important work to do.
Most people are curious about new ideas.
91
Problem
Short, complete statement of the problem
the pattern will solve.
Usually a meeting is just another
ordinary, impersonal event.
How do we get people to want to attend
our meeting?
02

11. Solution
Your proposed method of solving the
problem. Resolve important forces
determined by context; other forces may
be ignored.
Keep the target audience in mind.
Best Patterns are Generative
Have food at the meeting—donuts or
bagels in the morning, with coffee, tea,
and juice, and cookies and drinks in the
afternoon, lunch at noon-time.
12
Resulting Context
What happens if the solution is applied,
what forces resolved, what problems may
arise, what costs and benefits.
Just “problem solved” is not enough.
Food will turn a mundane meeting,
presentation or other gathering into a
more special event. If offered in the
beginning, it starts the meeting on a
positive note.
22

12. Rationale
Why the solution solves the problem.
Sell the pattern, teach the reader.
In Alexander’s pattern Communal Eating
(147), “eating plays a vital role in almost
all human societies as a way of binding
people together and increasing the extent
to which they feel like members of a group.
The act of eating together is by its very
nature a sign of friendship.”
32
Other Sections
Known Uses: A one-time occurrence is an
event. A double occurrence is a coincidence.
If it occurs more than twice, it’s a pattern.
Jim Coplien/Gerald Weinberg/Bunny Duhl
Related Patterns: Use, be used with, be
similar to other patterns
While the prospect of free food is nice,
Brown Bag can be used when funding is not
available. People can still eat together, even
if they bring their own food.
42

13. Ward’s Tips for Writing Patterns
Pick a whole area, not just one idea
Make a list of things you learned
Cast each item on your list as a solution
Now write each item as a Pattern
Try a four paragraph form where the second
paragraph ends with the pivotal "therefore”
Organize your patterns into sections
Write an Introduction
52
Joe’s Tips for Writing Patterns
Take some small 3x5 or equivalent cards
Brainstorm the catalogue of ideas
For each pattern, take a card and write
the problem solution as simple sentences
Add any other ideas such as forces,
related patterns, aliases, etc.
Organize the patterns
Use this to start writing the patterns
62

14. 82 level security.
Secure Access Layer Integrating application security with low
access to.
Limited View Allowing users to only see what they have
exceptions when needed.
Full View With Errors Provide a full view to users, showing
user environment.
Session Localizing global information in a multi-
privileges.
Roles Organizing users with similar security
repercussions.
Check Point Organizing security checks and their
log into the system.
Providing a security module and a way to Single Access Point
Intent Pattern Name
Security Pattern Example
72
) s el u r d n a s ei t r e p o r p – s ti n u ci m o t a
g ni ni b m o c y b s e r u t c u r t s x el p m o c e s o p m o c ( n oi ti s o p m o C ci m a n y D
) r e t e r p r e t ni
+ r e dli u b + y r o t c a f e vi t c el f e r : n r e t t a p e ti s o p m o c ( r e dli u B M O A
) y g e t a r t s + y r o t c a f e vi t c el f e r : n r e t t a p e ti s o p m o c ( y g e t a r t S ci m a n y D
) e h c a c y ti t n e h ti w d e t al e r e b y a M . n oi t c el f e r g ni s u
, s s al c e h t f o r e ni a t n o c d n a e m a n s s al c e h t g ni v a h t s uj , el y t s ” g ni d ni b
e t al “ a ni s e c n a t s ni g ni t a e r c r o f l u f e s u y r e v si si h t ( y r o t c a F e vi t c el f e R
) M V o t r ali mi s s M O A f o s e c n a t s ni s e h c a c ( g ni h c a C y ti t n E
) s w ei v f o s g ni r e d n e r e t el p m o c r o s t n e m g a r f s e h c a c ( g ni h c a C g ni r e d n e R
) M O A n a r o f w ei v e t el p m o c n a e t a e r c
o t s r e r e d n e r y t r e p o r p l a r e v e s s e t a r t s e h c r o ( r o t a r t s e h c r O g ni r e d n e R
) ytr e p or p a r of st n e m g arf I U s et ar e n e g( r er e d n e R ytr e p or P
AOM Pattern Catalogue

15. 03
.hcnual ot snoitacilppa-bus hcihw gnidiced rof msinahcem
a etaerc ,yrassecen fi dna ,metsys eht otni teg ot yaw eno ylno pu teS
Solution:
.noitamrofni yrassecennu retne ot evah
ton seod resu a ,yaw sihT .tniop yrtne taht ta dedeen noitamrofni eht
ylno tcelloc ot dezimotsuc eb nac noitacilppa na ot stniop yrtne elpitluM
.noitacilppa eritne eht rof dedeen
si taht noitamrofni resu eht fo lla tcelloc ot deen yam tniop yrtne elgnis A
.edoc etacilpud evah dluoc serudecorp ro swodniw nigol tnereffiD
.eruces eb ot deen
lla taht snoitacilppa-bus lareves fo etisopmoc a eb yam noitacilppa nA
.stnemnorivne tnereffid ni desu
eb ot ti rof reisae ti sekam noitacilppa na nepo ot syaw elpitlum gnivaH
Forces:
.noitacilppa eht gniretne rof ”srood edis“ dna ”,srood kcab“
”,srood tnorf“ elpitlum sah ti nehw etadilav ot tluciffid si ledom ytiruces A
Problem:
Single Access Point
92
. n oi t a cil p p a n a g ni s u t r a t s o t d e e n o h w
sresu tuoba dedeen noitamrofni labolg tcelloc dna sresu etadilav
ot ecalp eruces a gnidivorp yb siht sevlos tnioP sseccA elgniS
.gnissecorp retal rof tpek eb ot deen yam noitamrofni deilppus
-resu eht fo emos ,yllanoitiddA .smetsys lareves no detacitnehtua
eb ot deen yam resu a semitemoS .htiw gnitcaretni eb lliw
ti taht smetsys morf seludom ytiruces rehto htiw etargetni ot dna ,od
t o n n a c d n a n a c r e s u e h t t a h w p u t e s o t , m e t s y s e h t o t ni r e s u a g ol
ot yaw a deen lliw noitacilppa ehT .smetsys erutcurtsarfni rehto dna
,sesabatad ,smetsys gnitarepo ,gnikrowten htiw setacinummoc taht
noitacilppa na rof ytiruces edivorp ot drah si tI .yrtne fo tniop elgnis
a hguorht ssap tsum enoyreve nehw eetnaraug ot reisae si ytiruceS
Motivation/Context:
Single Access Point

16. Big Ball of Mud
Alias: SHANTYTOWN,
SPAGHETTI CODE
13
Big Ball of Mud - Context
Shantytowns are squalid, sprawling slums. Everyone
seems to agree they are a bad idea, but forces
conspire to promote their emergence anyway. What
is it that they are doing right? Shantytowns are
usually built from common, inexpensive materials
and simple tools. Shantytowns can be built using
relatively unskilled labor. Even though the labor
force is "unskilled" in the customary sense, the
construction and maintenance of this sort of
housing can be quite labor intensive. There is little
concern for infrastructure, since infrastructure
requires coordination and capital, and specialized
resources, equipment, and skills.
23

17. Big Ball of Mud - Context
Shantytowns emerge where there is a need for
housing, a surplus of unskilled labor, and a dearth
of capital investment. Shantytowns fulfill an
immediate, local need for housing by bringing
available resources to bear on the problem. Loftier
architectural goals are a luxury that has to wait.
Maintaining a shantytown is labor-intensive and
requires a broad range of skills. One must be able
to improvise repairs with the materials on-hand,
and master tasks from roof repair to ad hoc
sanitation. However, there is little of the sort of
skilled specialization that one sees in a mature
economy.
33
Big Ball of Mud - Context
All too many of our software systems are,
architecturally, little more than shantytowns.
Investment in tools and infrastructure is too often
inadequate. Tools are usually primitive, and
infrastructure such as libraries and frameworks, is
undercapitalized. Individual portions of the system
grow unchecked, and the lack of infrastructure and
architecture allows problems in one part of the
system to erode and pollute adjacent portions.
Deadlines loom like monsoons, and architectural
elegance seems unattainable.
43

18. 63
s el p m a x E
s e c n er ef e R
r o ht u A
h ct e k S
ses U n won K
s n r e t t a P d e t al e R
el a n oi t a R
t x e t n o C g ni tl u s e R
n oi t ul o S
m el b o r P
s ecr o F
t x et n o C
s e s ail A , e m a N
Let’s Write a Pattern!
53
performance
functionality, then focus on architecture and
Therefore, focus first on features and
. n r e c n o c g ni s s e r p a s a e r u t c e ti h c r a d r a g e r t o n
od ylpmis ssecorp tnempoleved eht eganam dna lortnoc
ohw elpoep eht ,netfO .worromot yb gnikrow gnihtemos
s d e e n r e m o t s u c e h t , n e t f o e r o M . e s a c e h t m o dl e s si h c u S
.elbaliava eb ot sneppah emit dna yenom sulprus sselnu ro
,ffo-etirw xat a hcus ,tifeneb etaidemmi elbignat emos si
ereht sselnu ,ti ssimsid ot sllib eht gniyap era ohw elpoep
eht rof ysae si tI .tnemtsevni mret-gnol a si erutcetihcrA
and under budget.
You need to deliver quality software on time,
Big Ball of Mud – Prob/Sol

19. 83
”.rohtua eht“ esu
;denoitnem reven si eman s’rohtua ehT .edam si tcatnoc
eye oN .elcric eht edistuo ”,llaw eht no ylf“ a semoceb
neht ,nrettap eht morf noitceles a sdaer ,sdnats rohtua ehT
.snigeb pohskrow eht erofeb nrettap eht daer stnapicitraP
stnapicitraP citehtapmyS
rezirammuS
rotaredoM
rohtuA
:seloR
.puorg eht yb dootsrednu si nrettap
eht woh no rohtua eht ot kcabdeef sedivorp taht ,rotaredom
lartuen ,gnorts a yb del ,seugaelloc detseretni fo elcric A
leirbaG…sgnihT gnikaM fo kroW eht & spohskroW 'sretirW
Writers Workshop
73
Patterns (Meszaros & Doble)
A Pattern Language for Writing

20. 04
. yr ots
d e t al e r n u n a sll e t e n o e m o s d n a t a e s t n e r effi d a s e k a t
e n o y r e v e , d e p p o h s k r o w e b o t si n r e t t a p r e h t o n a f I
. n oi t u bi r t n o c
s’ r o h t u a e h t s d u al p p a d n a s d n a t s p u o r g e h T
. st n e m m o c
ll a s n w o r o h t u a e h T . s n oi t s e g g u s o t yl e t ai r p o r p p a
t c a o t d e m u s s a si d n a t r e p x e n a d e r e di s n o c si r o h t u a e h T
. n oi s s u c si d si h t g ni r u d e z i g o l o p a r e v e n dl u o h s r o h t u a
e h T . s t n e m m o c y n a r e w s n a r o ni al p x e t o n dl u o h s r o h t u a e h T
. p u o r g e h t m o rf s t n e m m o c yfi r al c o t s n oi t s e u q s k s a
yl n o d n a k c a b d e ef e h t r of p u o r g e h t s k n a h t r o h t u a e h T
. el c ri c e h t o t ni k c a b r o h t u a e h t e ti v n I
. o w t r o t n e m m o c g ni s ol c e vi ti s o p a h ti w d n E
Writers Workshop
93
. p o h s kr o w e ht r etf a r o ht u a e ht r of
y p o c p u - d e k r a m a n o e d a m e b n a c s o p y t d n a s t n e m m o c l ai vi r T
. r e t al r o f s e u s si a t e m e v a S ” . d e t o n t ni o p “ , h ti w yll a u s u
, d n a h t a n r e t t a p e h t o t n oi s s u c si d s ni a r t s n o c r o t a r e d o m e h T
. n w o s ti n o d n a t s t s u m n r e t t a p e h T . r o h t u a
e h t r o f k a e p s r o y fi r al c t o n dl u o h s n r e t t a p e h t w o n k o h w e s o h T
. t n e m e v o r p mi d e t s e g g u s e h t n e h t d n a y ti n u t r o p p o
e h t e t a t S . t n e m e v o r p mi r of s n oi t s e g g u s , t x e N
. e n ol a e v a el dl u o h s
r o h t u a e h t t a h w y a S . s t n e m m o c e vi ti s o p h ti w ni g e B
.r ot ar e d o m r o r o ht u a e ht n a ht
r e h t o e n o e m o s y b n e vi g si n r e t t a p e h t f o y r a m m u s A
Writers Workshop

21. Conclusions
Good writing is not an accident—it
comes from dedication, focus, and
practice…. http://www.dreamsongspress.com/
Writing patterns is not necessarily hard
but can take patience and iterations
Just do it, thinking about it or theorizing
about it will not write the pattern
Get regular feedback specifically from
the Patterns Community
14