Introduction and Development Process
Peter Gorm Larsen
TIVDM1
Introduction and Development Process
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Agenda
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Administrative information about the course
What are VDM models and how are they validated?
Suggested Projects to undertake
The Process using the VDM++ and UML combination
Introduction and Development Process
2
Who is the teacher?
• Peter Gorm Larsen; MSc, PhD
• 18 years of professional experience
• ½ year with Technical University of Denmark
• 13 years with IFAD
• 3,5 years with Systematic
• 3/4 year with University College of Aarhus
• Consultant for most large defence contractors on large complex
projects (e.g. JSF)
• Relations to industry and academia all over the world
• Has written books and articles about VDM
• See http://home0.inet.tele.dk/pgl/peter.htm for details
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Contacting Details
• The most convenient way - email
pgl@iha.dk
• Or see me in my office. I live in at IHA in Room 413c.
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Teaching Material
• John Fitzgerald, Peter Gorm Larsen, Paul Mukherjee,
Nico Plat and Marcel Verhoef: Validated Designs for
Object-oriented Systems. Springer Verlag, 2005.
• Tool used during the course
http://www.vdmbook.com/tools.php
• Setup.exe files and documentation can also be found
under K:\from eit_staff to eit_stud\PGL
• Rational Rose for UML models to be requested from
K:\from eit_staff to eit_stud\PGL
• Run hostinfo.exe and send me the host name and
hostid such that I can generate a license file for you
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TIVDM1 web pages
• All information concerning this course including
lecture notes, assignments announcements, etc. can
be found on the TIVDM1 web pages
http://kurser.iha.dk/eit/tivdm1/
• You should check this site frequently for new
information and changes. It will be your main source
of information for this unit. The layout of the
WebPages should be fairly self explanatory
• Campus WebPages will be used only for mailing
information
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Education Form
• Confrontation with the teacher
• Tuesdays 14:30 – 15:45 in Room 424
• Thursdays 13:00 – 15:45 in Room 424
• Read in advance of each lecture
• Combination of
• Lessons teaching theory
• Strategy for lessons: quick intro to concepts and then usage in
larger examples
• Projects where theory is turned into practice
• Using VDMTools for projects
• Exam form
• 15 minutes oral examination without preparation + 5 minutes for
evaluation on the 7th of June 2006
• Oral examination will be centered around projects performed
• Projects will be reused and extended further in TIVDM2
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Focus in this course
• Focus is on
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Abstract modeling of realistic systems
Understanding the VDM concepts
Learning how to read models made in VDM++/UML
Learning how to write models in VDM++/UML
Learning how to validate these models
• Focus is not on
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Toy examples
Concurrency
Real-time requirements
Implementation
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Why have this course?
• To understand the underlying primitives for being able
to model complex computer systems
• To be able to comprehend the formulation of important
desirable properties precisely
• To be able to express important desirable properties
precisely
• To enable the formulation of abstract models in an
industrially applicable formal notation
• To validate those models to increase confidence in
their correctness
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Where is this used?
• Modeling critical computer systems e.g. for industries
such as
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Avionics
Railways
Automotive
Nuclear
Defense
• I have used this industrially for example at:
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Boeing, Lockheed-Martin (USA)
British Aerospace, Rolls Royce, Adelard (UK)
Matra, Dassault, Aerospatiale (France)
…
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Industrially Inspired Examples
• Chemical Plant Alarm Management
System
• A Robot Controller
• A Road Congestion Warning System
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Structure of the course
1.
2.
3.
4.
5.
6.
7.
TIVDM1
Introduction and development process (chap 1+2)
VDMTools and logic (chap 3)
Defining data and functionality (chap 4 + 5)
Modeling using unordered collections (chap 6)
Modeling using ordered collections (chap 7)
Modeling relationships (chap 8)
Course evaluation and repetition
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An email from an old (very good)
student
… At that time I understood that a formal specification would be an advantage
for big projects but I had no idea how desperately this is also needed in
smaller projects when there are many people involved. Today I do know:
At the moment I am working at BMW in the communications department.
We work on the integration of the car telephone (including a telematics unit
with GPS coordinates) into the overall car. There is a lot of interaction
between the telephone and the HMI of the car and there are different
versions and types of all the involved devices. There are also five
companies (BMW, Motorola, Siemens VDO, Harmann-becker, Alpine) who
develop the different units. The system should not be so complex because
many of the devices should (!) behave similarly. But the specifications we
write are English plain text (hundreds of pages), in our department more
than 10 people are involved and we do not know anymore how the devices
will behave ourselves...every external company has an own interpretation of
the specs and this interpretation changes over time. If you ask the same
person twice you get different answers (I frankly admit that I am no
exception)... You can imagine how "efficient" everything is and its a miracle
that the system still works (with a number of bugs though)...
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Agenda
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Administrative information about the course
What are VDM models and how are they validated?
Suggested Projects to undertake
The Process using the VDM++ and UML combination
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Vienna Development Method
• Invented at IBM’s labs in Vienna in the 70’s
• VDM-SL and VDM++
• ISO Standardisation of VDM-SL
• VDM++ is an object-oriented extension
• Model-oriented specification:
• Simple, abstract data types
• Invariants to restrict membership
• Functional specification:
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Referentially transparent functions
Operations with side effects on state variables
Implicit specification (pre/post)
Explicit specification (functional or imperative)
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Validation Techniques
• Inspection: organized process of examining the model
alongside domain experts.
• Static Analysis: automatic checks of syntax & type
correctness, detect unusual features.
• Testing: run the model and check outcomes against
expectations.
• Model Checking: search the state space to find states
that violate the properties we are checking.
• Proof: use a logic to reason symbolically about whole
classes of states at once.
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Validation via Animation
Execution of the model through an interface. The
interface can be coded in a programming language of
choice so long as a dynamic link facility (e.g. CORBA)
exists for linking the interface code to the model.
Formal
model
Interpreter
Interface
C++ or
Java
interface
code
Testing can increase confidence, but is only as good as
the test set. Exhaustive techniques could give greater
confidence.
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Agenda
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Administrative information about the course
What are VDM models and how are they validated?
Suggested Projects to undertake
The Process using the VDM++ and UML combination
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Possible projects
1. SAFER
2. Production Cell
3. Cash Dispenser
4. CyberRail
5. Conveyor belt from “Automation BSc course”
6. Projects from “Distributed Real-Time Systems”
7. Projects from “Specification of IT Systems”
8. Suggest your own project
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SAFER Overview
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SAFER References
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Simplified Aid For EVA Rescue
Presentation about mishap for SAFER
A 25 pages description of the system
Modelling SAFER using VDM-SL
Article about the SAFER VDM-SL model
VDM-SL + Mathematica simulation
Another CORBA interface to the VDM-SL model
A VDM++ model of SAFER
Article about the VDM++ model of SAFER
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Production Cell Overview
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Production Cell References
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Citations for the book about this
Project assignment from AUC/DTU about this
Slides about Production cell in different formalism
A book with a comparative study
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Cash Dispenser Overview
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The Cash Dispenser Model
• Model of a system of tills and a central resource.
• Customers interact with tills by inserting a card and
entering a PIN
• Central resources contains detailed records of
customers’ bank accounts
• “Illegal” cards are kept by the till.
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A Cash Dispenser Example
Tills
Central
Repository
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Requirement Specification
There are many tills which can access a central resource containing
the detailed records of customers’ bank accounts. A till is used by
inserting a card and typing in a PIN (Personal Identification Number)
which is encoded by the till and compared with a code stored on the
card. After successfully identifying themselves to the system,
customers may try to:
1. view the balance of their accounts
2. make a withdrawal of cash
3. ask for a statement of their account to be sent by post.
Information on accounts is held in a central database and may be
unavailable. In that case 1) above may not be possible. If the
database is available, any amount up to the total in the account may
be withdrawn, subject to a fixed daily limit on withdrawals. This
means that the amount withdrawn within the day must be stored on
the card. “Illegal” cards are kept by the till.
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Development Process
• Analysis (using VDM-SL with API animation)
• alternative to use cases
• abstraction from multiple tills
• Design (using Rose VDM++ Link with systematic
testing and API animation)
• abstraction from possible failures of tills
• Implementation (with concurrent VDM++ model and
automatic Java code generation combined with user
interface)
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UML Class Diagram
Clock
Till
CentralResource
cardOk : bool = false
Create()
Validate()
CardInside()
GetBalance()
InsertCard()
ReturnCard()
IsLegalCard()
CardValidated()
MakeWithdrawal()
RequestStatement()
Encode()
date : Date
illegalCards : set of Card`CardId = {}
numberOfTries : map Card`CardId to nat = {|->}
maxNumberOfTries : nat = 3
-resource
Create()
AddAccount()
GetBalance()
Withdrawal()
IsLegalCard()
PostStatement()
AddIllegalCard()
IncrNumberOfTries()
ResetNumberOfTries()
NumberOfTriesExceeded()
-clock
Letterbox
-letterbox
PostStatement()
GetLastStatement()
{ordered}
-statements
Account`AccountId
-accounts
Account
-curCard
-retainedCards
0..*
0..1
Card
code : Code
cardId : CardId
accountId : Account`AccountId
GetCode()
GetCardId()
GetAccountId()
Create()
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balance : nat
transactions : seq of Transaction = []
dailyLimit : nat = 2000
GetDate()
SetDate()
0..*
Letter
date : Clock`Date
name : Cardholder`Name
address : Cardholder`Address
balance : nat
transactions : seq of Account`Transaction
Create()
Create()
AddCard()
GetBalance()
GetCardIds()
Withdrawal()
MakeStatement()
ValidTransaction()
Sum()
TransactionsInvariant()
DateTotal()
Cardholder
name : Name
address : Address
Card`CardId
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-cards
Create()
GetName()
GetAddress()
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Cash Dispenser References
• The Cash Dispenser Example at different abstraction
levels
• The VDM++ non-concurrent version of the Cash
Dispenser model
• The VDM++ Concurrency version of the Cash
Dispenser model
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CyberRail Overview
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CyberRail References
• The CyberRail web page
• CyberRail, Concept and Future
• CyberRail articles from web page
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Conveyor belt
Overview
Discard 1
Speed guard
SP1
Photoelectric
sensor
LE1
Bar code
reader
Photoelectric
sensor
LE1
Cylinder 1
Cylinder 1 in
SW2
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Introduction and Development Process
Discard 2
Photoelectric
sensor
LE1
Motor
M1
Cylinder 2
Cylinder 1 out
SW1
Cylinder 2 in
SW4
Cylinder 2 out
SW3
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Components and Control
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Components
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Control
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M1: Engine to pull the belt forward or backward.
Speed control: Indication that the belt is running.
Cylinder 1 and 2: Pneumatic cylinders for moving off bricks.
Switch 1 and 2: Indication of cylinder 1’s position.
Switch 3 and 4: Indication of cylinder 2’s position.
Barcode reader: Reads the bar code on a brick.
Photo cell 1: Register a brick right after the bar code reader.
Photo cell 2: Register a brick right before discard 1.
Photo cell 3: Register a brick right before discard 2
Operator selection of sorting principles
Alarms for cylinders
Alarm if the belt stops while processing is ongoing
Alarm is photo cell discover bricks that have not been processed by
bar code reader
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System-level functionality
in VDM-SL
types
Stream = seq of Brick;
Brick ::
code : Code
color : <Red> | <Green> | <Yellow>;
Code = token;
functions
ConveyorBelt: Stream * Code * Code -> Stream * Stream * Stream
ConveyorBelt(input,code1,code2) ==
mk_([input(i) | i in set inds input & input(i).code = code1],
[input(i) | i in set inds input & input(i).code = code2],
[input(i) | i in set inds input
& input(i).code not in set {code1,code2}])
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Establishments of Groups
• For each of these possible projects the participants
should go together to form small groups of 2 to 3
persons per group
• Groups should decide this week which project to work
on during this course
• Every week (2 – 6) every group will present to the
entire class how their project is getting along
• The project will be further extended and analyzed with
concurrency and real-time aspects in the TIVDM2
course
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Anticipated Plan with Projects
• Week 2: Read existing material about the project and
formulate a new requirements definition for the project
to undertake with focus on the purpose of the model
to develop
• Week 3: Complete UML class diagram for the project
with signatures for operations/functions
• Week 4+5: Model and validate functionality using
VDM++
• Week 6: Report with the project is handed in to the
teacher
• Week 7: Evaluation of insight gained by using the
model-driven approach combining VDM++ and UML
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Agenda

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
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Administrative information about the course
What are VDM models and how are they validated?
Suggested Projects to undertake
The Process using the VDM++ and UML combination
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Steps to Develop a Formal Model
1.
2.
3.
4.
Determine the purpose of the model.
Read the requirements.
Analyze the functional behavior from the requirements.
Extract a list of possible classes or data types (often from nouns) and
operations (often from actions). Create a dictionary by giving explanations to
items in the list.
5. Sketch out representations for the classes using UML class diagrams. This
includes the attributes and the associations between classes. Transfer this
model to VDM++ and check its internal consistency.
6. Sketch out signatures for the operations. Again, check the model's
consistency in VDM++.
7. Complete the class (and data type) definitions by determining potential
invariant properties from the requirements and formalizing them.
8. Complete the operation definitions by determining pre- and post conditions
and operation bodies, modifying the type definitions if necessary.
9. Validate the specification using systematic testing and rapid prototyping.
10. Implement the model using automatic code generation or manual coding.
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A Chemical Plant
alarm
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expert
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A Chemical Plant Requirements
1. A computer-based system is to be developed to manage the alarms of this
plant.
2. Four kinds of qualifications are needed to cope with the alarms: electrical,
mechanical, biological, and chemical.
3. There must be experts on duty during all periods allocated in the system.
4. Each expert can have a list of qualifications.
5. Each alarm reported to the system has a qualification associated with it
along with a description of the alarm that can be understood by the expert.
6. Whenever an alarm is received by the system an expert with the right
qualification should be found so that he or she can be paged.
7. The experts should be able to use the system database to check when they
will be on duty.
8. It must be possible to assess the number of experts on duty.
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The Purpose of the VDM++ Model
The purpose of the model is to clarify the rules
governing the duty roster and calling out of
experts to deal with alarms.
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Creating a Dictionary
• Potential Classes and Types (Nouns)
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Alarm: required qualification and description
Plant: the entire system
Qualification (electrical, mechanical, biological, chemical)
Expert: list of qualifications
Period (whatever shift system is used here)
System and system database? This is probably a kind of
schedule.
• Potential Operations (Actions)
• Expert to page: when an alarm appears (what's involved?
Alarm operator and system)
• Expert is on duty: check when on duty (what's involved?
Expert and system)
• Number of experts on duty: presumably given period
(what's involved? operator and system)
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Guideline 1
Nouns from a dictionary should be modeled as types if, for
the purposes of the model, they need have only trivial
functionality in addition to read/write.
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Sketching an Alarm
Defined as a VDM++ class:
class Alarm
instance variables
reqQuali: Expert`Qualification
descr
: String;
end Alarm
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Alternative Alarm
Alarm could also have been defined as a composite
type:
Alarm :: reqQuali : Expert`Qualification
descr
: String
Then if a is of type Alarm:
a.descr is the description of a
a.descr : String
a.reqQuali : Expert`Qualification
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Guideline 2
Create an overall class to represent the entire system so
that the precise relationships between the different
classes and their associations can be expressed
there.
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Guideline 3 and 4
Whenever an association is introduced consider its
multiplicity and give it a rôle name in the direction in
which the association is to be used.
If an association depends on some value, a qualifier
should be introduced for the association. The name of
the qualifier must be a VDM++ type.
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Initial Class Diagram
class Plant
instance variables
public alarms
: set of Alarm;
public schedule : map Period to set of Expert;
end Plant
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Guideline 5
Declare instance variables to be private or protected to keep
encapsulation. If nothing is specified by the user, private is
assumed automatically.
class Expert
instance variables
private quali: set of Qualification;
end Expert
class Alarm
instance variables
private descr
: String;
private reqQuali: Qualification;
end Alarm
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Guideline 6 and 7
Use VDMTools to check internal consistency as soon as
class skeletons have been completed and before any
functionality has been introduced.
• Definition of types missing
• To be updated in the respective classes
• Resynchronized with the UML model
class Plant
types
Period = token;
end Plant
Tokens are useful for abstract models where unspecified
values are to be used.
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Adding Quantification and String
class Expert
types
Qualification = <Mech> | <Chem> | <Bio> | <Elec>
end Expert
class Alarm
types
public String = seq of char;
instance variables
descr
: String;
reqQuali : Expert`Qualification;
end Alarm
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Guideline 8
Think carefully about the parameter types and the result
type as this often helps to identify missing connections
in the class diagram.
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Updated UML Class Diagram
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Guideline 9
Document important properties or constraints as
invariants.
class Plant
...
instance variables
alarms : set of Alarm;
schedule: map Period to set of Expert;
inv forall p in set dom schedule & schedule(p) <> {};
end Plant
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Guideline 10
When there are several alternative ways of performing
some functionality, use an implicit definition so that
subsequent development work is not biased.
ExpertToPage: Alarm * Period ==> Expert
ExpertToPage(a, p) ==
is not yet specified
pre a in set alarms and
p in set dom schedule
post let expert = RESULT
in
expert in set schedule(p) and
a.GetReqQuali() in set expert.GetQuali();
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Will the Qualification exist?
• How can we be sure that an expert with the required
qualification exists in the required period?
• We need to add an invariant to the instance variables
of the Plant class
• That is using guideline 11
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Guideline 11
When defining operations, try to identify additional
invariants.
instance variables
alarms : set of Alarm;
schedule: map Period to set of Expert;
inv forall p in set dom schedule & schedule(p) <> {};
inv forall a in set alarms &
forall p in set dom schedule &
exists expert in set schedule(p) &
a.GetReqQuali() in set expert.GetQuali();
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Further Operations inside Plant
class Plant
operations
…
public NumberOfExperts: Period ==> nat
NumberOfExperts(p) ==
return card schedule(p)
pre p in set dom schedule;
public ExpertIsOnDuty: Expert ==> set of Period
ExpertIsOnDuty(ex) ==
return {p | p in set dom schedule &
ex in set schedule(p)};
end Plant
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Guideline 12
Try to make explicit operation definitions precise and clear
and yet abstract compared to code written in a
programming language.
import java.util.*;
class Plant {
Map schedule;
Set ExpertIsOnDuty(Integer ex) {
TreeSet resset = new TreeSet();
Set keys = schedule.keySet();
Iterator iterator = keys.iterator();
while(iterator.hasNext()) {
Object p = iterator.next();
if ( ( (Set) schedule.get(p)).contains(ex))
resset.add(p);
}
return resset;
}
}
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Final UML Class Diagram
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Guideline 13
Whenever a class has an invariant on its instance
variables and it has a constructor, it is worth placing the
invariant in a separate function if the constructor needs
to assign values to the instance variables involved in
the invariant.
functions
PlantInv: set of Alarm * map Period to set of Expert ->
bool
PlantInv(as,sch) ==
(forall p in set dom sch & sch(p) <> {}) and
(forall a in set as &
forall p in set dom sch &
exists expert in set sch(p) &
a.GetReqQuali() in set expert.GetQuali());
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To be used inside Plant
Constructor
class Plant
…
public Plant: set of Alarm *
map Period to set of Expert ==>
Plant
Plant(als,sch) ==
( alarms := als;
schedule := sch
)
pre PlantInv(als,sch);
end Plant
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Review Requirements (1)
R1: A computer-based system managing this plant is to
be developed.
Considered in the Plant class definition and the
operation and function definitions.
R2: Four kinds of qualifications are needed to cope
with the alarms: electrical, mechanical, biological,
and chemical.
Considered in the Qualification type definition
of the Expert class.
R3: There must be experts on duty at all times during
all periods which have been allocated in the system.
Invariant on the instance variables of class Plant.
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Review Requirements (2)
R4: Each expert can have a list of qualifications.
Assumption: non-empty set instead of list in class
Expert.
R5: Each alarm reported to the system must have a
qualification associated with it and a description which
can be understood by the expert.
Considered in the instance variables of the Alarm
class definition assuming that it is precisely one
qualification.
R6: Whenever an alarm is received by the system an
expert with the right qualification should be paged.
The ExpertToPage operation with additional invariant
on the instance variables of the Plant class definition.
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Review the Requirements (3)
R7: The experts should be able to use the system
database to check when they will be on duty.
The ExpertOnDuty operation.
R8: It must be possible to assess the number of
experts on duty.
The NumberOfExperts with assumption for a
given period.
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Testing The Model
• Examine the file Test.rtf using MS Word. This is a
test driver class.
• Start up VDMTools with the project alarm.prj.
• Go to the Project configuration menu (found at
Project->Configure) and add the files Test.rtf,
Plan.rtf, Expert.rtf and Alarm.rtf
• Syntax and type check the entire project.
• Start up the interpreter and initialize the model.
You are now ready to test and debug your model...
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Executing the model
• In the interpreter window, at the vdm> prompt, create
a test driver object named t using the create
command:
create t := new Test()
• Now call t’s Main operation using the print command
print t.Main()
• Since this yields a reference to a Plant object, we
can use the result for testing. For instance
print t.Main().NumberOfExperts(
mk_token("Monday day"))
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Running Tests
Execute your model to answer the following questions:
• How many experts are on duty during Tuesday day
(period p3)?
• Which period has the most experts on duty?
• Is John on duty on Monday night?
• Is Ringo qualified to deal with electrical alarms?
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Potential for using CORBA API
• VDMTools has a CORBA API that can be used for
example to make a GUI for other stakeholders
• Easy validation of understanding at early stages
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Summary
• What have I presented today?
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Administrative information about the course
An intro about VDM and validation techniques
Potential projects to work on in this course
A first glimpse of the process of constructing a model
• What do you need to do now?
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TIVDM1
Read chapter 1 to 3 of the book
Get VDMTools installed and start looking at the manuals
Get Rational Rose installed and run hostinfo and send email
Form groups for the projects
Select the project to work on
Introduction and Development Process
71
Quote of the day
Abstraction, difficult as it is, is the
source of practical power.
Bertrand Russell
(1872 - 1970)
TIVDM1
Introduction and Development Process
72