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Writing Code for Other People
Tom Mullen
The barriers and techniques of human intelligence
are starting to be uncovered by psychologists.
There are remarkable parallels between the
cognitive model and principles established by
software designers.
It is as if the jigsaw puzzle that software designers
have been working on has been turned over to
reveal another picture on the back, the very same
picture that psychologists have been building...
Overview

Cognitive Psychology (Chunking and Memory)

Analogies

Psychologists Definition

Code Structures

Fundamental Metric

Using the Cognitive Model
Overview

Cognitive Psychology (Chunking and Memory)

Analogies

Psychologists Definition

Code Structures

Fundamental Metric

Using the Cognitive Model
Elements of Cognitive Psychology
Chunking and Memory


A chunk is “a collection of memory elements
having strong associations with one another
but weak associations with elements within
other chunks”
Structured Design Principle: “maximise
cohesion and reduce coupling”
Chunking and Memory


STM Capacity Limit

CRC Model

Refactoring
STM Time Limit

Indirection cost
LTM Structure
Discrimination Nets
Cognitive Model
Summary
Conjecture: Current software languages and
design principles guide a programmer to
produce code that is a direct textual
representation of the memory network of
the solution within the brain (subject to the
constraints of short term memory).
Overview

Cognitive Psychology (Chunking and Memory)

Analogies

Psychologists Definition

Code Structures

Fundamental Metric

Using the Cognitive Model
Overview

Cognitive Psychology (Chunking and Memory)

Analogies

Psychologists Definition

Code Structures

Fundamental Metric

Using the Cognitive Model
Analogies
Meeting Room Analogy
Gentner Classification
Overview

Cognitive Psychology (Chunking and Memory)

Analogies

Psychologists Definition

Code Structures

Fundamental Metric

Using the Cognitive Model
Analogy Template
Analogy Patterns in Software
Analogy Patterns in Software
Attribute Only [Map]
Map exchangeCountry = new HashMap();
exchangeCountry.put("CBOT","US");
exchangeCountry.put("LIFFE","England");
Na
Aa
Nv
Av
Analogy Patterns in Software
Statement Shape
private boolean isValid()
{
if (expirationDate == null ||
!( expirationDate.getTime() > 0 ) )
return false;
if (contractNumber == null ||
!(contractNumber.longValue() > 0) )
return false;
Analogical Translations
Analogy Patterns in Software
Method Name (Prefix)
public void visitExpression(Node a){};
public void visitBlock(Node a){};
public void visitFile(Node a){};
Analogy Patterns in Software
Application Level

Running Instances are Literal Similarities of
one another.

Configuration details the attributes

IOC mechanisms allow operations
Overview

Cognitive Psychology (Chunking and Memory)

Analogies

Psychologists Definition

Code Structures

Fundamental Metric

Using the Cognitive Model
Parlay?

In Pirates of the Caribbean what was Captain
Barbossa's response to Elizabeth Swan's
demand that the Pirate Code required him to
put her ashore safely?
4 minus Analogies Rule
The core fundamental metric of software de-sign
is that software should be chunked in
elements of four (or fewer) after allowing for
any number of varieties of analogies.
The Pirate Code
“… more what you’d call ‘guidelines’ than actual
rules”
– Capt. Barbossa, Pirates of the Caribbean: The
Curse of the Black Pearl
Overview

Cognitive Psychology (Chunking and Memory)

Analogies

Psychologists Definition

Code Structures

Fundamental Metric

Using the Cognitive Model
Using the Cognitive Model

Can be taught using life experiences

Is the foundation of software design principles

Design principles still need to be learned!

Use to discover new principles?
Conclusion



Cognitive Psychology: Detailed the strong
mapping between the cognitive model and
design principles.
Chunking Analogies: The two primary
disciplines in good software design are:

recognising & coding analogies

chunking.
Used these results to discover the “4 minus
analogies” rule.
tom@tom-mullen.com
Questions? http://www.chunkinganalogies.com