Introduction to Software Architecture

Bredemeyer Consulting
Web: http://www.bredemeyer.com
Introduction to
Software Architecture

Software Architecture Workshop
Introduction Slide 2
Preamble: An Architecture Story
Copyright © 1999-2017 Bredemeyer Consulting
http://www.bredemeyer.com

Articles of
Confederation
Virginia Plan
Madison’s Notes AmendmentsThe Constitution
Federalist papers
Expressions of the Architecture

Alexander Hamilton
John Jay
Benjamin Franklin
Signing of the Constitution. September 17, 1787
The Architects
James Madison
“Architect of the Constitution”

Debrief: Lessons for Architects

Workshop Objectives
• Advance in our ability to create an
architecture that is
 Good: is technically sound
 Right: meets the stakeholder needs (business, customers,
developers, managers, etc.)
 SUCCESSFUL: is delivering value

Introduction to Software Architecture
Overview
• What: characterizing software architecture
concerns and decisions
• Why: understand the contribution it makes
• How: the (visual) architecting process
• and build a roadmap of what we will do over next 4 days
• Who: architects—role, responsibilities and
capabilities
• Where and When: organizational and
lifecycle context

What is Software Architecture?
’92

’03

Architecture: What?

Architecture: Decisions!

Architecture: Which Decisions??!

Architecture: Significant Decisions!

Big Ball of Mud Architecture:
High Cost of Change
“If you think good
architecture is expensive,
try bad architecture”
– Brian Foote
“You reach for the
banana, and get the
entire gorilla”
– Michael Stahl

Actually, it looks more like this
Image: from Undoing the harm of layers by Bjørn Bjartnes

Modular Structure(s):  Cost of Change!
• Isolate impact of change
• Isolate arenas of uncertainty and experiment
• Increase reversibility, replaceability,
• Increase responsiveness/adaptability
• Reduce complexity
 Divide and conquer
 “we have to keep it crisp, disentangled, and simple if we
refuse to be crushed by the complexities of our own
making...” – Dijkstra

’03

’92
Architecture: What?

Architecture: Parts and Relations!
“Software architecture refers to the high level
structures of a software system [..] Each
structure comprises software elements,
relations among them, and properties of both
elements and relations.”
— wikipedia 2017
(after Clements et al, 2010)

[intermezzo]
“Everything that needs to be said
has already been said. But since no
one was listening, everything must
be said again.
— André Gide

Architecture: is Design!

Design: What?
"Everyone designs who
devises courses of action
aimed at changing
existing situations into
preferred ones."
— Herbert Simon

How: Finding the (Natural) Shape
“I go along with the natural
makeup”…
“when I come to the tricky
parts, I slow down”
— Chuang Tzu: “The
Dexterous Butcher”

Separation: Outside/Inside
— Ambrose Bierce, Devil’s Dictionary
ABATIS, n. [1.] Rubbish in front
of a fort, to prevent the rubbish
outside from molesting the
rubbish inside.
Image: Engineering and the Mind’s Eye
“Design things to make their
performance as insensitive to
the unknown or uncontrollable
external influence as practical.”
— Eb Rechtin

Separation of Concerns
Image:
alistair.cockburn.us/Hexagonal+architecture
[Ports and
adapters]
Hexagonal Architecture

Boundaries
“There was a wall. It did not look important. It
was built of uncut rocks roughly mortared. An
adult could look right over it, and even a child
could climb it. Where it crossed the roadway,
instead of having a gate it degenerated into
mere geometry, a line, an idea of boundary.
But the idea was real. It was important. For
seven generations there had been nothing in
the world more important than that wall.
Like all walls it was ambiguous, two-faced.
What was inside it and what was outside it
depended upon which side of it you were on.”
— Ursula K. Le Guin, The Dispossessed

Abstractions
As programmers we deal
with abstractions all the
time and we have to invent
them in order to solve our
problems
— Michael Feathers

How: Finding Natural Abstractions
Image: martinfowler.com/bliki/BoundedContext.html
Bounded Contexts in DDD

Components and Responsibilities

How: Factor and Refactor
“The responsibility of architecture
is the architecture of responsibility.”
— Jan van Til/Tom Graves
Does this component have a
cohesive identity or purpose — a
single responsibility at the level of
abstraction of the abstraction?

How: Heuristics
“Fundamentals that remain fundamental”

Architecture: What [Again?]?

System: What?
“A system is an
interconnected set of
elements that is
coherently organized in
a way that achieves
something”
— Donella Meadows
Image: donellameadows.org

Essence of Systems is
• Relationships
• Interfaces
• Form
• Fit
• Function
— Eberhardt Rechtin

Illustration By Apocryphal Example
trying to be an airplane”
— Wim Roelandts

System: What?
“The defining
properties of any
system, are properties
of the whole, which
none of the parts have.
If you take the system
apart, it loses its
essential properties”
— Russell Ackoff

Design: to Get More the Properties We
Want…

Architecture: Parts, Relations, Properties

Minimalist Architecture
Those decisions that must
be made from a system
perspective
• system outcomes
• across boundaries
Dana Bredemeyer

Design Across
“Design is not just what
it looks like and feels
like. Design is how it
works.”
— Steve Jobs

How: Design Across
Elements and Interactions: How it Works
Posit structure
Explore behavior
Revise structure
How will this
work?What is it made
(up) of?
How does this
contribute to/inhibit
desired properties?

Design Across: Structure and Behavior
What
ARCHITECTURE
STRUCTURE
interfaces
elements and
relationships
How
BEHAVIOR
Logical
Conceptual

Design Is How It Works
What
(system view)
HowWhat
(user view)
ARCHITECTURE
STRUCTUREBEHAVIOR
CAPABILITIESCONTEXT
Why
v v
How well
FUNCTION PROPERTIES
architecturally significant mechanisms

Architecturally significant?
demands (forces, properties, …) on the
system that are challenging, push the limits,
raise risks, require design attention

LMAX Disruptor Mechanism
Challenges:
A trading platform
needs very low latency
- trades have to be
processed quickly
because the market is
moving rapidly.
A retail platform adds
complexity because it
has to do this for lots
of people.
Source: Martin Fowler http://martinfowler.com/articles/lmax.html

Founding Classics
“The Federalist Papers
are arguments that
support different parts of
the design of the
Constitution.”
– Alan Kay, 1995

Federalist 51
addresses
• separation of powers
• checks and balances

Develop a Theory of the System

Annotate and Explain Design (Views)

Keep an Architecture Decision Record
Title: short noun phrase
Context: describe the forces at play,
probably in tension
Decision: describe our response to
these forces
Status: proposed, accepted,
deprecated or superseded
Consequences: describe the resulting
context, after applying the decision
— Michael Nygard, Documenting
Architecture Decisions, Nov 2011

Architecture as Intention and Reflection
System Design Intention
(what should be)
System Design Reflection
(what is)

Reflection: tools to view
static structure

Also: Just… take note(s)!
Leonardo da Vinci’s notebooks
Observe the system
Develop and share theory
• of operation
(interactions, resolution
of forces, outcomes)
• of relation of structure to
function/properties

Design Stays Inside the Box?
No, no it does not!

Connecting the Dots: relating decisions to
strategies, needs and forces they address

Develop a Theory of the System

Context Factors
Image source: Sarah Mei on Twitter
“Design quality is not a
property of the code. It's
a joint property of the
code and the context in
which it exists.”
– Sarah Mei

"Always design a thing by considering it in its
next larger context" — Eliel Saarinen
Context System-in-Context
(use, dev, ops)
System
(Ecosystem)
Architecture
structure and
mechanisms
“Requirements”
design of system
capabilities
Strategy
ecosystem interventions

the elephant in the room
it’s all design!
•Strategy sets design
direction
•“Requirements” is design
of system capabilities and
properties
•Architecture is design to
achieve them

Architecturally Significant
Structurally significant
• Organizing structure
• Architecturally significant
mechanisms
• Structural integrity and
sustainability
Strategically significant
• game shapers and game changers
What is make
or break?
What impacts
how we
compete?
"I wasn't the one pushing things in the wrong direction, but I should have been the one to stop it." — Chad Fowler

Not Just Good, but Right and Successful!
What
(system view)
HowWhat
(user view)
ARCHITECTURE
STRUCTUREBEHAVIOR
CAPABILITIESCONTEXT
Why How well
FUNCTION PROPERTIES
good?right?successful?

Separation of Concerns
Context Capabilities Architecture

Co-Design of What the System Is
and How it is Built …
right system–built right
Its messy! But so is any
alternative!
We either acknowledge that
design is a process of learning
what the system needs to be,
and is becoming, or it lets us
know the hard way!

Decision Models: Places to Put Things
Architecture Strategy
Architecture
Architecture Decision Record
Conceptual Architecture
Logical Architecture
Execution Architecture
• Architectural vision, principles, styles, key concepts and mechanisms
• Focus: high-level decisions that will strongly influence the structure of
the system; rules certain structural choices out, and guides selection
decisions and tradeoffs among others
• Structures and relationships, static and dynamic views,
assumptions and rationale
• Focus: decomposition and allocation of responsibility,
interface design, assignment to processes and threads
• Architecture Decision Record; open issues; guidelines, policies,
mechanisms, design patterns; frameworks, infrastructure and standards
• Focus: guide engineers in creating designs that maintain the integrity of
the architecture

Architecture Views
Conceptual Architecture
Logical Architecture
Execution Architecture
• Architecture Diagram, CRC-R cards, Design sketches for key mechanisms
• Focus: identification of components and allocation of responsibilities to
components; conceptually address key design challenges
• Updated Architecture Diagram (showing interfaces), Interface specifications,
Component specifications and usage guides, Mechanism designs
• Focus: design of component interactions, connection mechanisms and
protocols; interface design and specification; providing contextual information
for component users
• Process and Deployment Views
• Focus: assignment of the runtime component instances to processes,
threads and address spaces; how they communicate and coordinate; how
physical resources are allocated to them

Architecture: Why?
• Purpose is not to be a map
of the system, though views
are useful as maps
 Locate (places to find things;
places to put things)
• Purpose:
 to do design (to do design is
to improve the design) to get
more the outcomes we want

Architecture: When
• Earliest Responsible Moment?
• Last Responsible Moment?
“What is the most important
think we should be thinking
about at this extraordinary
moment?”
– Buckminster Fuller

Is the Jar Full?

Is the Jar Full Now?

How: Architecting
• Heuristics help identify and guide tradeoffs
• Visual design and design visualization
• Iterations

Iterations
You think it’s messy?
Well, it’s messier than that!

Fallible We Are
“I confess that there are several parts of
this constitution which I do not at
present approve, but I am not sure I
shall never approve them: For having
lived long, I have experienced many
instances of being obliged by better
information, or fuller consideration, to
change opinions even on important
subjects, which I once thought right, but
found to be otherwise. It is therefore that
the older I grow, the more apt I am to
doubt my own judgment, and to pay
more respect to the judgment of others.”
— Benjamin Franklin

Feynman on Fallibility
“We are never definitely right,
we can only be sure we are
wrong!”
“The first principle is that you
must not fool yourself and you
are the easiest person to fool”
— Richard Feynman

(Ad)Vantage Point
“A change of
perspective is
worth 80 IQ points”
— Alan Kay

Alternatives: Rule of Three
“If you haven’t thought
of three possibilities,
you haven’t thought
enough.”
— Jerry Weinberg

Iterations
You think it’s messy?
Well, it’s messier than that!
Actively weeding out weak
ideas, focusing and
improving the design, means
feedback loops, within
feedback loops

Who: Architects
• As Leaders
 Look across boundaries, and further out in time, and
asking: What does
• the code need,
• the team need,
• the system need,
• operations and users need
to thrive and be sustaining?
 What needs to be done, that isn’t being done?

Architects Lead
to Design Integrity
• An architect is a tech(nical) lead(er) -- but
architect puts emphasis on *system*
*design*, that is on being a leader who
facilitates and ensures system design
integrity. Not just design cohesion, but
resilience, more...

Design Integrity
“Design is inherently
about what ought to be
made… it is inherently
ETHICAL.”
— Jabe Bloom
Image: Jabe Bloom, as he
known on twitter (@cyetain)

Who: Architects
• Discussion: In an Agile context,
 Do we still need architects?
 (If yes) Do architects also code?
 (Also if yes) What characterizes (good) architects?

More?
• Software Architecture Workshop
Denver, CO, June 11-14, 2018
http://www.bredemeyer.com/Workshops/architecture_workshop_overview.htm

Introduction to Software Architecture

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