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Systems Theory Introduction and course OverviewStefan RatschanDepartment of Digital Design Faculty of Information Technology Czech Technical University in Prague
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Systems TheoryIntroduction and Overview
Stefan Ratschan
Department of Digital DesignFaculty of Information Technology
Czech Technical University in Prague
Evropsky socialn fond Praha & EU: Investujeme do vas budoucnosti
Stefan Ratschan (FIT CVUT) MIE-TES 1 / 28
My Technical Data
Stefan Ratschan
Building A, room 1029
http://www.cs.cas.cz/~ratschan (Consultation Hours!)
Rest (and most) of the time:
Institute of Computer Science of theAcademy of Sciences of the Czech Republic
Pod Vodarenskou vez 2
Metro stanice Ladv
Stefan Ratschan (FIT CVUT) MIE-TES 2 / 28
Introduction and Survey
Which study program at which university?
Mother tongue?
Who speaks/understands Czech?
Who is afraid of the word theory?
Who knows what UML means?
Petri net
Turing machine
Logic course?
Stefan Ratschan (FIT CVUT) MIE-TES 3 / 28
What is a System?If you want to have some high-brow definitionwith references to Greek, Latin, Chinese philosophers:look up your favorite encyclopedia.
Computer systems: software systems, hardware systems, network systems
But: In the past, job of someone with a degree in computer science:
not any more!
and if you want an interesting andwell-paid job, it is not enough toknow about computer systems.
Stefan Ratschan (FIT CVUT) MIE-TES 4 / 28
Todays and tomorrows computer systems (example)
Stefan Ratschan (FIT CVUT) MIE-TES 5 / 28
Todays and tomorrows computer systems (example)
Interaction with
organizational systems
biological systems (cells, organisms, ...)
ecological systems
economical systems
social systems
Especially: trains, airplanes, cars, mobile phones
That is: complex technical devices
So: system =something complex that we encounter as computer scientists
Today there are computational devices almost everywhere,and a computer scientist should be able to handle this.
Stefan Ratschan (FIT CVUT) MIE-TES 6 / 28
Your Systems?
Usage for examples throughout the semester
Bachelor thesis?
Other systems?
Stefan Ratschan (FIT CVUT) MIE-TES 7 / 28
PolymathHowever, nobody has the slightest chance to be an universal expert
Stefan Ratschan (FIT CVUT) MIE-TES 9 / 28
No need for being a polymathInstead: theory
Liquids always flow downwards
Abstract description and explanation of reality
Abstract: independent of concrete situation,can be applied in many situations (an advantage!)
Scientific theories
Objective: independent of a concrete person/place/time,can be applied by anybody/anwhere/anytime
Systems Theory: description and explanation of systems behavior,that is valid
for everybody, everywhere, and all the time.
Differently from HTML constructs, Java library etc. This is a university!Stefan Ratschan (FIT CVUT) MIE-TES 10 / 28
Goal of Course
Provide orientation in a world of systems
How possibilities does mankind have for describing systems?
organizational systems
biological systems (cells, organisms, ...)
ecological systems
economical systems
social systems
technical and computer systems
Scientific theories: Principles that hold
for everybody,
everywhere, and
all the time.
Stefan Ratschan (FIT CVUT) MIE-TES 11 / 28
Characteristics of Complex Technical Systems
Human-built
Highly complex: design teams
Huge: > 1000 for aeroplanes
Diverse: Mechanical engineers, software engineers, control engineers,chip designers, etc.
Often safety critical
Reactive: continuous interaction with environment
Concurrent: many functions in parallel
Sometimes: dynamic structural changes (e.g., new cars added)
Interaction of physical and electronical components(cyber-physical system)
Stefan Ratschan (FIT CVUT) MIE-TES 12 / 28
Physical vs. Electronic Components
More and more functions taken over by digital electronics(e.g., brake-by-wire, x-by-wire, x-by-wireless)
Design costs of electronics more and more dominating costs ofphysical system
Stefan Ratschan (FIT CVUT) MIE-TES 13 / 28
Resulting Control Loop
Analog-to-digital (A/D) converter
Stefan Ratschan (FIT CVUT) MIE-TES 14 / 28
How to Design Such Systems?
Example: train
Highly complex: first decompose into components
Which ones?
traction
train body
signalling
electricity
air conditioning
lighting
doors
on-board information, communication, and entertainment
tilting system
Stefan Ratschan (FIT CVUT) MIE-TES 15 / 28
Further Scenario (simplified V model)
we want a train
we want tractions signalization etc.
design traction, signalization etc.
test traction, signalization etc.
compose the parts
test the whole train
What will happen?
If engineers do not start to fight(they cannot talk to each other),
if they produce anything reasonable at all(sub-systems still immensely complex),
if they resulting designs can be put together (each sub-system takesdifferent assumption about other sub-systems),
if the resulting train runs at all, it will crash on the track.Stefan Ratschan (FIT CVUT) MIE-TES 16 / 28
ProblemsWe see and check the whole product only at the end!
Movie: Tacoma Narrows bridgecollapse
V-model only fancy trial-and error
We want
detect problems already at the beginning
if possible, automatically
How to achieve this?Stefan Ratschan (FIT CVUT) MIE-TES 17 / 28
Stefan Ratschan (FIT CVUT) MIE-TES 18 / 28
ModelAbstract system representation
Abstract: Partial description that hides details (i.e., hides complexity) and describes only those aspects of a system that
are important for the task at hand.
For example: We are looking for the mensa. Is this useful??
Stefan Ratschan (FIT CVUT) MIE-TES 19 / 28
Hierarchy of System Models Informal requirements:
Train should follow signalling standard for Czech tracks (Partially) formal specification (but still: What do we want?) High level operational models (How should it work? e.g., finite state
automaton, Scilab demo) VHDL, C program Circuit design, machine code . . .
Hierarchy of abstractions:higher levels hide complexity,lower levels provide more details
Cycle (simplification, idealization): model based design Create system model Check if o.k. (if possible automatically) If necessary use models with lower level of abstractionStefan Ratschan (FIT CVUT) MIE-TES 20 / 28
Result
Advantages:
we work with whole system during the whole design process
from the beginning we can analyze/debug whole system
tool support: automatic translation between models (compiler, code generator) simulation (demo?) testing formal verification
Therefore: problems, and errors can be found early
Therefore:
Stefan Ratschan (FIT CVUT) MIE-TES 21 / 28
Model Classification
Formal/informal (using natural language, figures etc.)
Dynamical vs. static models
Adaptive vs. fixed structure models
Stefan Ratschan (FIT CVUT) MIE-TES 22 / 28
Goal of Course (practical version):Basic situation:
We want to design a system (software, train, mobile application etc.)that fulfills its specification
The method of trial and error is too expensive and not reliableenough.
Hence, before building the system, wedesign a model and analyse it automaticlly
Fancy big question:
How can we describe and computationally analyze complex systems?
Concrete goal: Learn formalisms, techniques, and tools formodeling and analysis of complex technical systems, such that
you can function in such a design process, and
you will produce high-quality systems.
Stefan Ratschan (FIT CVUT) MIE-TES 23 / 28
Preliminary List of Lectures
1. Introduction and Overview
2. Basics of Practical Logic
3. Communicating Finite State Machines I
4. Communicating Finite State Machines II
5. Specification: Temporal Logic
6. Bounded Model Checking
7. Boolean Satisfiability Checking
8. Unbounded Model Checking
9. Petri Nets
10. Timed Automata
11. Continuous, hybrid systems
12. Hybrid sytems: verifications
13. Probabilistic models
Stefan Ratschan (FIT CVUT) MIE-TES 24 / 28
SourcesSlides on Edux
I will not follow a certain textbook.
On the slides of the individual lectures I will provide references to sources
Lecture notes on Edux (under development)
You will not need them if you attend the lectures
If you miss some lectures, you will need additional sources
Lectures slides will not contain all information,I will draw examples, figures etc. onto the whiteboard
Be careful with wikipedia!
A large part of the lecture material is not there. If it is there, it often contains mistakes, bad explanations etc.
Wikipedia cannot replace understandingStefan Ratschan (FIT CVUT) MIE-TES 25 / 28
AssignmentsThe assignments will not be about
blindly applying some already known method to new data
Real life is never about blind application of known methods.
For solving assignments you will have to
understand the description of the problem
read, understand, and use the corresponding definitions
solving a new problem.
This you will need throughout your life.
Everything you need, I will present in the lecture(including some examples).
In assignment class you should be able to answer questions like:
According to which definition does this hold?
How did you use this definition?
Stefan Ratschan (FIT CVUT) MIE-TES 26 / 28
Final ExamYou will be allowed to use any book, printouts of slides etc.
o.k., so Ill just relax during the semester,at the exam I will anyway be able to find the answers in books
This will not work!
The final exam will consist of two types of examples:
Examples of the same or similar typeas the assignments during the semester.
Examples, that test whether the student is able to apply the theoryfrom the lecture on his/her own in a new context
Time:
will be easily enough for well prepared people. People, who will start to list in slide printouts at the exam,
will have problems with time.Stefan Ratschan (FIT CVUT) MIE-TES 27 / 28
Next Lecture
Basis of all models: Logic
Logic is very often taught as a subjectdescribing the foundations of mathematics and computer science(Hilbert calculus, resolution algorithm and so on).
Which is great, but as a result,many students lack the ability to apply logic in everyday life
Next lecture: Basics of practical logic
From the theoretical point of view nothing new.
If are fluent in logic and its usage, no need to come(lecture notes, Chapter 1 and 2 without 1.9 and 2.2)
Stefan Ratschan (FIT CVUT) MIE-TES 28 / 28