Ivica Crnkovic Mälardalen University Department of Computer Science and Engineering

, 04/22/23Software engineering and Scientific Methods

Ivica CrnkovicMälardalen University

Department of Computer Science and Engineering [email protected]

http://www.idt.mdh.se/~icc

mailto:[email protected]

http://www.idt.mdh.se/personal/icc

http://www.idt.mdh.se/personal/icc


ContentsContents

What is Software Engineering? Software Engineering and Science Methods of Software Engineering Software Engineering Research

Example – Software architecture


What is Software Engineering?What is Software Engineering?

Software engineering is an engineering discipline which is concerned with all aspects of software production from the early stages of system specification through to maintaining the system after gone into use.

Ian Sommerville, Software Engineering

We need further explanation of: Engineering discipline All aspects of software production


EngineeringEngineeringEngineers make the things work Solving problems

understand the problem analyze the problem

Find solutions Constructing the solution from parts that address the problem's

various aspects - do a synthesis To achieve the goal engineers

apply theories, methods and tools from different disciplines Search for solutions even when there is not theory or methods


PROBLEM

Subproblem 1 Subproblem 3Subproblem 2

Analysis of a problemAnalysis of a problem

Identify different aspects of the problem

Arrange the problems in clearly defined and understandable sub-problems


SOLUTION

Solution 1Solution 3

Solution 2 Solution 4

The synthesisThe synthesisFind solutions for subproblems

Put together solutions to a consistent view

Provide (make) a solution


Engineering Example – the Vasa ShipEngineering Example – the Vasa Ship

1625 King Gustav II Adolf decided to start build Wasa

1628 - maiden voyage.

Length- 69 metresLength- 69 metresMaximum width - 11.7 metresMaximum width - 11.7 metresFrom keel to the top of the main mast - 52.5 metresFrom keel to the top of the main mast - 52.5 metresHeight of the stern - 19.3 metres Height of the stern - 19.3 metres Crew: Crew: 445 men, Seamen – 145445 men, Seamen – 145, , Soldiers - 300 Soldiers - 300

ArmamentArmament 64 guns64 guns

Thousands of people involved in the projectThousands of people involved in the projectSelecting wood, building different partsSelecting wood, building different partsProviding food, other services Providing food, other services

A master piece of work!


Vasa – Example of Bad EngineeringVasa – Example of Bad Engineering the ship capsized on her maiden

voyage in the harbor of Stockholm.

Why did the Vasa capsize?


Why did the Vasa capsize? Why did the Vasa capsize?

The Vasa capsized because it was not stable;

The Vasa capsized because the building process (or in terms of software engineering, the

development project) was inadequate.


How to calculate stability?How to calculate stability?

Gravity forceGravity forceShip weightShip weight

Ship’s center of gravityShip’s center of gravity

BuoyancyBuoyancy(bärkraft)(bärkraft)

Center of buoyancyCenter of buoyancy(water) displacement(water) displacement

The forces are of equal size and in the opposite directionsThe forces are of equal size and in the opposite directions


The ship heels at an angleThe ship heels at an angle

Ship’s center of gravityShip’s center of gravityCenter of buoyancyCenter of buoyancy(water displacement)(water displacement)Has moved rightHas moved right

hh h – leverage effecth – leverage effect(påtryckning)(påtryckning)


Leverage effect (Moment)Leverage effect (Moment)

http://members.aol.com/PhysicsDad/calcphys/lecture.htmlhttp://members.aol.com/PhysicsDad/calcphys/lecture.html

Torque is defined as the product Torque is defined as the product of radius, force, and the sine of the of radius, force, and the sine of the angle between force and radius: angle between force and radius:

t = r F (sin(X))t = r F (sin(X))

XX


The ship heels at an angleThe ship heels at an angle

hh

h – leverage effecth – leverage effect(påtryckning)(påtryckning)

This Torque (Moment)This Torque (Moment)will force thewill force theShip to return back Ship to return back


hh

The ship is unstableThe ship is unstableh – leverage effecth – leverage effect(påtryckning)(påtryckning)

Torque has change the directionTorque has change the directionThe ship will capsizedThe ship will capsized

hh


The ship is stableThe ship is stable

hh

hh

If the center of gravity is very low – the ship will be stableIf the center of gravity is very low – the ship will be stable


Why the ships heel?Why the ships heel?

hh

Because of wind!Because of wind!Or waves…Or waves…


Wind

S1

S2

A

B

Torque

Stability Curve Stability Curve


Why did Vasa capsize?Why did Vasa capsize?

Engineering – Solve problems even when there is no formal theory

Experience – best practices Observations Rules of thumb Processes to ensure the feasibility of problem solving COULD VASA BE SUCSSESFULLY BUILT IN SPITE OF

LACK OF THEORY? WHAT DID PROJECT FAILED TO DO?


Other reasons why Vasa capsized?Other reasons why Vasa capsized? Resource & budget plan. The project was delayed and in its

later phases, there was enormous pressure to finish work on time.

Project management. The main builder (or in modern terms, the project manager) unfortunately sickened and died during the building of the ship, and the consequence was weak management and very poor coordination of the groups building different parts.

Changes in requirements. The original requirement for one gun deck was changed to two gun decks when the building of the ship had already begun. Because the king was behind the decision, its possible consequences were not analyzed.

Conflicting requirements and trade-off analysis. The Vasa was intended to be a new type of ship combining superior sailing characteristics and maneuverability with overwhelming striking force.


Other reasons why Vasa capsized?Other reasons why Vasa capsized? Design changes during the construction. The dimensions of

the ship were changed several times during its construction with no proper analysis of the consequences.

System design vs. detailed design. In many parts the design of the system was not clear and completed, and the final design was shaped during the implementation. The entire process is reminiscent of prototype building. In combination with poor project coordination this resulted in inadequate dimensions of some parts, such as insufficient space for ballast.

Scalability. Vasa was designed as a smaller ship, and its dimensions were merely proportionally increased.

Validation. The stability and other tests were primitive and not well performed. (Test: running across the deck)


Vasa Disaster – Similar do Software ProjectsVasa Disaster – Similar do Software Projects

Similar situation in software development project No formal/theoretical background for requirements and

solution Feasibility of the requirements not analyzed Changes in requirements during the project work Time and Budget not properly planned No proper verification Bad quality assurance Shortage in knowledge in new disciplines....


Engineering vs. Software EngineeringEngineering vs. Software Engineering Many similarities

Methods and procedures Base objectives and goals

Many differences Difference between software and hardware/the real world

Software – no physical limitsNot visibleModifiableMore complex

Different theories and methods used Different experiences, traditions Different maturity level


All aspects of Software DevelopmentAll aspects of Software Development

Aspects Technical (how technicaly solve the problem) Organisational (how to organize people) Financial Marketing Professional and ethical responsibility Research and Science


SOFTWARE ENGINEERING

COMPUTER SCIENCE CUSTOMER

Theories

Principles, Methods and Tools to Solve

Problem andConstruct sSolutions

ProblemComputer Functions

Computer Science Vs. Software EngineeringComputer Science Vs. Software Engineering

SolutionSoftware EngineeringSoftware EngineeringResearch & ScienceResearch & Science

OTHER SCIENCES


Computer Science Vs. Software EngineeringComputer Science Vs. Software Engineering

COMPUTER SCIENCEAlgorithms and data structures

Programming languagesArchitecture

Numerical and symbolic computationOperating systems

Software methodology and engineeringDatabases and information retrieval

Artificial intelligence and roboticsHuman-computer communication

Social, ethical, and professional issues

SOFTWARE SOFTWARE ENGINEERINGENGINEERING

In many cases a defuseIn many cases a defuse

boundaries between SE and CSboundaries between SE and CS


Methods and Technologies Methods and Technologies

Requirements Analysis Design Implementation Delivery MaintenanceTest

Software/Systems Engineering Methods

Different Technologies

Service

Solution

Phases


SE disciplines - examplesSE disciplines - examples Project management Development processes Requirements engineering Reverse engineering Test and Verification Software Maintenance Software Architecture Object-oriented modelling Software analysis Formal specification Software reliability

Real-time Tools and environments Software Configuration

Management Software engineering and the

Internet Component-based SE Software Metrics Education Software Economics ......


Software Engineering Methods - ExamplesSoftware Engineering Methods - Examples

Project Management

Software Development Models and Processes support

Analyse/design methods (UML, OOP, Formal methods, ...)

Programming Methods /Languages

Configuration Management

Component-based Software Engineering (CBSE)

Customer support, Maintenance

Test and Verification

Architectural analysis (tradeoff analysis, quality, attributes…)

Requirements Engineering

Requirements Analysis Design Implementation Delivery MaintenanceTest Service


What is then Software Engineering Research?What is then Software Engineering Research?

Analyzing natures of problems and their solutionsFinding more general principles that SE can useDeveloping methods and tools Implementing principles on new problem domains……


Software Engineering ResearchSoftware Engineering Research

Different methods used SEExemplified by Software Architecture

Presentation extracted from Mary Show’s presentation on ICSE 2001 in Toronto

http://www-2.cs.cmu.edu/~Compose/paper_abstracts/etaps-2002.html

http://www-2.cs.cmu.edu/%7ECompose/paper_abstracts/etaps-2002.html


REAL WORLDREAL WORLDPractical problemPractical problem

REAL WORLDREAL WORLDPractical SolutionPractical Solution?


Research ModelResearch Model


Example: Software ArchitectureExample: Software Architecture

The software architecture of a program or computing system is the structure or structures of the system, which comprise software components, the externally visible properties of those components and the relationships among them

L. Bass, P. Clements, R. Kazman, Software Architecture In Practise, Addison Wesley, 1998


Software architecture – system decompositionSoftware architecture – system decomposition

SystemSystem

subsystemsubsystem SubsystemSubsystem

componentcomponent componentcomponent componentcomponent


Recurring structures that occur in software systemsAS = {Component types,Connector types,Constraints}

Next step - Architectural StyleNext step - Architectural Style

Component and Connector Types

Layered Abstract MachinesBuss

Shared Repository

Component and Connector Types

Pipe and Filter


Next step: Aspects of Software ArchitectureNext step: Aspects of Software Architecture

Connector

RolePort

Attachment

(sub)System

Arch Component

Representation

Elements and Form

Rationale Describes how the architecture satisfies system requirements for both

functional and extra-functional properties.


<<subsystem>>ComAIComA

Next step: FormalizationNext step: Formalization

<<subsystem>>ComBIComB

<<subsystem>>ComCIComA

ConceptualArchitecture

Example - UMLExample - UML


SE Research phasesSE Research phases

Research Questions

Research Results

Result Validation


SummarySummary

Software Engineering is oriented on practical things from the real word Understanding problems, providing solutions

SE uses methods and tools for solving the problems from different disciplines

SE research Understanding principles Defining principle for solving the problems Developing tools and methods

Ivica Crnkovic Mälardalen University Department of Computer Science and Engineering

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