Ten Commandments of
Formal Methods: A decade later
Jonathan P. Bowen Michael G. Hinchey
Museophile Limited, UK Loyola College in Maryland
Baltimore, USA
www.jpbowen.com
(Also visiting academic, (Also NASA)
University College London)
See IEEE Computer, 39(1):40–48, January 2006.
Based on Dagstuhl workshop, Germany, 8–12 May 2006.

Dagstuhl Seminar 06191
Rigorous Methods for Software Construction
and Analysis, 8–12 May 2006

Choosing a formal method – difficult
ASM
GC6
B
Z
VSR-net

Background – formal methods
Academics vs. industrial practitioners
Theory vs. practice
Still little used in general practice
Size of community critical
It is clear to the best minds in the field
that a more mathematical approach is
needed for software to advance much.
― Bertrand Meyer

The Flat Earth
Society
Cf. formal methods
community…
— Gerard J. Holzmann
FMICS 2005 (Lisbon)
conference queue! ►

Ten Commandments
… ten years later
J.P. Bowen & M.G. Hinchey,
IEEE Computer,
April 1995 & January 2006
He proclaimed to you his
covenant, which he
commanded you to keep:
the Ten Commandments,
which he wrote on two
tablets of stone.
“Can’t I just read your URL?”
― Deuteronomy 4:13, 10:4, Ex.34:28
vl.fmnet.info/moses-url

Thou shalt choose an
appropriate notation.
Notations are a frequent complaint…
but the real problem is to understand
the meaning and properties of the
symbols …
… you will cultivate an appreciation
of mathematical elegance and style.
By that time, the symbols will be
invisible ...
The great advantage of mathematics
is that the rules are simpler than
those of natural language
― C.A.R. Hoare

Which notation?
Various notations:
ASM (testing?)
B (development?)
Z (specification?)
Etc. – 95 under
vl.fmnet.info

Beware
Panaceas!
Cf. Formal
methods

Caviat
Emptor!
Cf. Software

Name Combines Advantage Ref.
Combined Temporal B, temporal Adds time to the Bonnet et
B logic B-Method al. (1995)
formal
methods ZCCS Z, CCS Combines CCS Galloway
process algebra and
add to the and state based Stoddard
confusion! aspects of Z (1997)
CSP OZ Z, CSP Combines Z and Fischer
CSP (2000)
If I could say it [13]
in words there Object Z Z, OO Adds OO to Z Smith
would be no principles, (2000)
temporal
reason to paint. logic
― Edward Hopper Object-Z, π- Adds π-calculus
PiOZ Taguchi
calculus style dynamic et al.
(1882–1967) comm. (2004)
capabilities to
Object-Z

Thou shalt formalize
but not overformalize.
Need for formality
Formality vs. informality
Levels of use
Strange as it seems, no amount of
learning can cure stupidity, and
formal education positively fortifies it.
― Stephen Vizinczey

Level Name Involves
Levels 0 Formal Formal notation
Specification used for specifying
of use requirements only;
no analysis/proof
1 Formal Proving properties
Development / and applying
Verification refinement
calculus
Cost vs.
2 Machine Use of theorem
correctness Checked prover/checker
(quality) Proofs / Model tool to prove
checking consistency/
integrity.

Thou shalt estimate costs.
Estimation models (CoCoMo II, …)
Total cost of ownership (TCO)
Quality of people varies (c10:1?)
Cost (salary) varies (c2:1?)
Still an inexact “science”
I think that God in creating Man somewhat
overestimated his ability.
― Oscar Wilde (1854–1900)

200
Requirements
GRO78
Target Cost Overrun, Percent phase costs
OMV
TDRSS compared with
160 IRAS
project overrun
Gali
HST
costs
GOES I-M TETH
120 (source: NASA)
LAND76
CEN
EDO (recent start)
MARS
ACTS
ERB77
COBE
80 STS
CHA.REC LAND78
GRO82
ERB80
SEASAT
40 UARS VOYAGER HEAO
EUVE/EP
DE Ulysses ISEE
SMM PIONVEN IUE
0
Ref: NASA/W. Gruhl 0 5 10 15 20
Requirements Cost/Program Cost, percent

Cost of proofs
Mathematics – simple theorems,
deep proofs (decades or centuries)
Cf. software – complicated specs
& programs, shallow proofs
(B, 90–95% automated, 5–10%
manual, weeks or months).
Fermat’s Last Theorem (in Toulouse)
an + bn ≠ cn (n>2)
— Pierre de Fermat (1601–1635)

Hand vs.
machine
checked
proofs
Blackboard at Dagstuhl workshop!

Thou shalt have a formal
methods guru on call.
Communication/understanding important
Project management
Technology transfer
Support organizations (FME, ForTIA, …)
An expert is a person who has made all
the mistakes that can be made in a very
narrow field.
― Niels Bohr (1885–1962)

Technology transfer
E.g.: Z notation
Courses (academia & industry)
Textbooks (good choice)
Tools (type-checkers, provers, …)
Web resources – vl.fmnet.info
Discussion – comp.specification.*
User Group (meetings)
Standards (see later)

Formal Methods Europe
FME: started with European funding
Industry, academia and government
Now more international in scope
FM’06: 14th Symposium
Hamilton, Canada, 21–27 Aug 2006
www.fmeurope.org
FME Wiki:
www.fmeurope.org/twiki/bin/view

ForTIA
Formal Techniques Industry Association
Founded through European CoLogNET
Computational Logic Network and FME
at FM2003 symposium, Pisa
Subgroup of FME
Technology transfer to industry
See: www.fortia.org

Thou shalt not abandon
thy traditional
development methods.
UML
Object-orientation
Model-Based Development (MBD)
A great many of those who ‘debunk’
traditional... values have in the background
values of their own which they believe to be
immune from the debunking process.
― C. S. Lewis (1898–1963) The Abolition of Man

UML & OO methods
Unified Modeling Language
pUML (precise UML)
Combined with B-Method tools
Object-Z
Perfect Developer (Java/C++)
Escher Technologies
Applied to self, proving c95% of
approx. 130,000 verification conds
Cf. Atelier-B tool?

Thou shalt document
sufficiently.
Case studies – success & failure
Process important
Textbooks (c10 Z vs. c1000 Java!)
I have always tried to hide my own efforts and
wished my works to have the lightness and
joyousness of a springtime which never lets
anyone suspect the labours it cost.
― Henri Matisse (1869–1954)

Google Book Search books.google.com

Textbooks
for courses
Resistance by
students
Resistance even
by academics
Professional
society
accreditation
(e.g., BCS)

Software Specification Methods
Henri Habrias &
Marc Frappier (eds.)
Springer-Verlag, 2001
and ISTE, 2006
Z, SAZ, B, OMT, Action
Systems, UML, VHDL,
Estelle, SDL, E-LOTOS,
JSD, CASL, Coq, Petri
Nets, TLA.
Process of producing
a formal spec…

Wikipedia
Z notation category.
Add ASM, B-Method,
… categories?
en.wikipedia.org/wiki/Formal_methods See also:
en.wikipedia.org/wiki/Category:Formal_methods

Thou shalt not compromise
thy quality standards.
$360B loses due to poor software quality (2002)
ISO 9000 revised (2000)
IEC 61508-3 functional safety standard (1998)
00-55 UK MoD standard updated (1997)
00-56 Issue 3 for hardware-software (2005)
FMs mandated for safety-related software
If people knew how hard I worked to get my
mastery, it wouldn't seem so wonderful at all.
― Michelangelo Buonarroti (1475–1564)

Z Standard
ISO/IEC 13568
Long process (1990s)
Final Committee Draft
– accepted in 2001!
Important for tools and
industrial use
ASM, B, … ?

Thou shalt not
be dogmatic.
Listen to industry’s problems
Choice may depend on expertise
Good tool support important
Combined theorem proving/model
checking (e.g., Yices from SRI)
… And I am unanimous in that!
― Molly Sugden, a.k.a. Mrs. Slocombe
Are You Being Served? BBC TV (1972–1993)

Community Z Tools
Open systems model – e.g.,
Community Z Tools (CZT) initiative
Sourceforge project:
czt.sourceforge.net

Open source initiatives
European RODIN project (2004–2007):
Rigorous Open Development Environment
for Complex Systems
rodin.cs.ncl.ac.uk
Support for B# (“B sharp”, cf. C#)
rodin-b-sharp.sourceforge.net
See also B4free: www.b4free.com
HOL 4: hol.sourceforge.net
Jape: sourceforge.net/projects/jape

Thou shalt test,
test, and test again.
Even short programs complex
Small changes can cause large problems
Easy to change, not easy to be correct
I believe the hard part of building software to
be the specification, design and testing of this
conceptual construct, not the labor of
representing it and testing the fidelity of the
representation.
― Frederick P. Brooks, Jr., No Silver Bullet

FORTEST Network
Formal methods and testing
www.fortest.org.uk
UK academia and industry (3 years funding)
Regular workshops (last 19 Dec 2005, London)
“Landscapes” ACM Surveys paper to appear
Book in preparation for Springer LNCS (2007)

Formalization of testing criteria
Z notation – readable
Existing criteria (e.g., MC/DC)
Modified Condition/Decision Coverage
New criteria (e.g., RC/DC)
Reinforced Condition/Decision Coverage
(false actuation type errors detected)
Reduces ambiguity, increases understanding
See: Formal Aspects of Computing, 18(1):42–62,
March 2006 & STVR, 15(1):21–40, March 2005
[Work with Sergiy Vilkomir & Kalpesh Kapoor]
See: www.cafm.lsbu.ac.uk/fortest

Formalization of testing criteria
Using the Z notation. E.g.:

Thou shalt reuse.
Possible if “formal”
Cheaper at higher levels of abstraction
Levels of complexity
The biggest difference between time
and space is that you can't reuse time.
― Merrick Furst

Levels of complexity
25 lines of informal requirements
250 lines of (formal) specification
2,500 lines of design description
25,000 lines of high-level program code
250,000 machine instructions of object code
2,500,000 CMOS transistors in hardware!

Reflection
Oui, l'œuvre sort plus belle
D'une forme au travail
Rebelle,
Vers, marbre, onyx, émail.
[Yes, the work comes out more beautiful from
a material that resists the process, verse,
marble, onyx, or enamel.]
— Théophile Gautier (1811–1872) L'Art

Grand Challenge 6
1 of 7: Dependable Systems Evolution
Sir Tony Hoare et al.
Verifying Compiler (this century!)
Workshops: e.g., Zurich, Dagstuhl
Further information: www.fmnet.info/gc6

Verified Software Repository
Cf. QED Pro Quo repository – www.qpq.org
Case study software, tools, challenges
Mondex Electronic Purse (security)
Dagstuhl Seminar (10–14 June 2006)
UK EPSRC VSR-net network (2005–2008)
EPSRC project proposal
Last meeting (York, UK, 5–6 October 2006)
Further information: www.fmnet.info/vsr-net

Conclusion
Continued niche market for critical systems
Especially safety and security
Hardware as well as software (model checking)
Tools very important (open source?)
Breakthrough with theorem proving/model checking?
Breaking the “5,000” glass ceiling?
… in this area my academic colleagues are
doing exactly what they should do: developing
and propagating an indispensable technology
so that it will be available when “the world out
there” undeniably needs it.
― Edsger W. Dijkstra (1930–2002)

Applied Formal Methods
"You know my methods.
Apply them."
— Sir Arthur Conan Doyle
The Sign of Four (1890)
URL: vl.fmnet.info
Virtual Library

SEFM 2007 conference
IEEE conference on Software
Engineering and Formal Methods
Keyworth Centre, London South Bank
University, UK, 10-14 September 2007
URL: www.iist.unu.edu/SEFM07
Submission deadline: 31 March 2007

ABZ08: ASM, B, Z meeting
ASM, B, Z user groups & VSR-net
2008 Jean-Raymond Abrial’s 70th birthday
(inventor of Z and B)
BCS London offices, 15-18 September 2008
c/o BCS Formal Aspects of Computing
Science (FACS) Specialist Group
Free venue for BCS SGs (120 people max)
1 day joint, 2 days in parallel, 1 day VSR-net
workshop (space dividable)

ASM, B, Z meeting – people
ASM – Egon Börger (Pisa)
B – Michael Butler (Southampton)
Z – Jonathan Bowen (London)
VSR-net – Jim Woodcock (York)
Local organization – Paul Boca (London)
Industrial case study – Ian Oliver (Nokia, Helsinki)

www.fmnet.info
The End Keyworth Centre ▲
Hubble in clean room ▼
sel.gsfc.nasa.gov