Software Engineering-I Module-I Introduction to S/W Development Lecture-1

Software Engineering-I Shahbaz Ahmed 2 Reference Books “Software Engineering” by Ian Somerville 7 th Edition “Software Engineering Theory and Practice” by Shari, Lawrance & Pfleeger 2 nd Edition “Fundamentals of Object Oriented Design in UML” by Miler Page-Jones

Software Engineering-I Shahbaz Ahmed 3 An Introduction to Software Engineering

Software Engineering-I Shahbaz Ahmed 4 Requirements for this Class You are proficient in a programming language, but you have no experience in analysis or design of a system You want to learn more about the technical aspects of analysis and design of complex software systems

Software Engineering-I Shahbaz Ahmed 5 Objectives To introduce software engineering and to explain its importance To set out the answers to key questions about software engineering To introduce ethical and professional issues and to explain why they are of concern to software engineers

Software Engineering-I Shahbaz Ahmed 6 Objectives cont… Appreciate Software Engineering: Build complex software systems in the context of frequent change Understand how to produce a high quality software system within time while dealing with complexity and change Acquire technical knowledge (main emphasis) Acquire managerial knowledge

Software Engineering-I Shahbaz Ahmed 7 Understand the Software Lifecycle Process vs Product Learn about different software lifecycles Greenfield Engineering, Interface Engineering, Reengineering Acquire Managerial Knowledge

Software Engineering-I Shahbaz Ahmed 8 What is an Engineering System? Engineering system = capability for the development of systems, hardware, or software Components: People Process Technology Knowledge Interfaces: Internal (among components) External (to stakeholders and customers)

Software Engineering-I Shahbaz Ahmed 9 Primary Relationship Diagram People Process Technology Knowledge Engineering System (Components of an engineering system)

Software Engineering-I Shahbaz Ahmed 10 What do these terms mean? People: the people who are part of the engineering system Engineers Infrastructure support personnel Managers Process: the processes used by the people or technology to accomplish the functions of the engineering system Technology: the tools and mechanisms of the engineering system Knowledge: value-added contextual information necessary to the development and operation of the engineering system

Software Engineering-I Shahbaz Ahmed 11 Engineering System Capability Resources and Requirements Systems, Software, & Hardware Products ….Time….

Software Engineering-I Shahbaz Ahmed 12 Why Software Engineering? Software development is hard ! Important to distinguish “easy” systems (one developer, one user, experimental use only) from “hard” systems (multiple developers, multiple users, products) Experience with “easy” systems is misleading One person techniques do not scale up Analogy with bridge building: Over a stream = easy, one person job Over River Severn … ? ( the techniques do not scale)

Software Engineering-I Shahbaz Ahmed 13 Why Software Engineering ? The problem is complexity Many sources, but size is key: UNIX contains 4 million lines of code Windows 2000 contains 10 8 lines of code Software engineering is about managing this complexity.

Software Engineering-I Shahbaz Ahmed 14 FAQs about software engineering What is software? software process? software engineering? software process model? What is software engineering? What is the difference What is the difference between between software engineering and computer science? between between software engineering and system engineering?

Software Engineering-I Shahbaz Ahmed 15 FAQs about software engineering What are the costs of software engineering? What are software engineering methods? What is CASE (Computer-Aided Software Engineering) What are the attributes of good software? What are the key challenges facing software engineering?

Software Engineering-I Shahbaz Ahmed 16 Software engineering (Criticality) The economies of ALL developed nations are dependent on software. More and more systems are software controlled Software engineering is concerned with theories, methods and tools for professional software development. Expenditure on software represents a significant fraction of GNP in all developed countries.

Software Engineering-I Shahbaz Ahmed 17 Software costs Software costs often dominate computer system costs. The costs of software on a PC are often greater than the hardware cost. Software costs more to maintain than it does to develop. For systems with a long life, maintenance costs may be several times development costs. Software engineering is concerned with cost- effective software development.

Software Engineering-I Shahbaz Ahmed 18 Introduction Software engineering is an interesting subject. In order to understand this subject we will need to look at a number of examples and case studies. And we will need to see how we can develop good software and how it could be improved in different scenarios? Before we move on to software engineering we need to understand what software actually is.

Software Engineering-I Shahbaz Ahmed 19 What is software? Computer programs and associated documentation + data Software products may be developed for a particular customer or may be developed for a general market Software products may be Generic - developed to be sold to a range of different customers Specific (custom) - developed for a single customer according to their specification

Software Engineering-I Shahbaz Ahmed 20 Why software is important? Used in Business decision-making Modern scientific investigation and engineering problem solving Games Embedded systems Similarly in many other fields like education, office automation, Internet applications etc, software is being used. Due to its central importance and massive use in many fields it is contributing a lot in terms of economic activity started by the software products. Billions and trillions of dollars are being invested in this field throughout the world every year.

Software Engineering-I Shahbaz Ahmed 21 What is software engineering? Software engineering is an engineering discipline which is concerned with all aspects of software production Software engineers should adopt a systematic and organised approach to their work use appropriate tools and techniques depending on the problem to be solved, the development constraints and the resources available New software can be created by developing new programs, configuring generic software systems or reusing existing software.

Software Engineering-I Shahbaz Ahmed 22 Software Engineering as defined by IEEE IEEE defines Software Engineering as “The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software; that is, the application of engineering to software.” Software Engineering is defined by Ian Somerville as “A field concerned with all aspects of software production’ Software engineering is not just concerned with the technical processes of software development but also with activities such as software project management and with the development of tools, methods and theories to support software production”.

Software Engineering-I Shahbaz Ahmed 23 What is the difference between software engineering and computer science? Computer science is concerned with theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software. Computer science theories are still insufficient to act as a complete underpinning for software engineering (unlike e.g. physics and electrical engineering). This sums up software Engineering as ”SE is the process of utilizing our knowledge of computer science in effective production of software systems.”

Software Engineering-I Shahbaz Ahmed 24 What is the difference between software engineering and system engineering? Software engineering is part of System engineering System engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering System engineers are involved in system specification, architectural design, integration and deployment

Software Engineering-I Shahbaz Ahmed 25 What is a software process? A set of activities whose goal is the development or evolution of software Generic activities in all software processes are: Specification - what the system should do and its development constraints Development - production of the software system Validation - checking that the software is what the customer wants Evolution - changing the software in response to changing demands

Software Engineering-I Shahbaz Ahmed 26 Software Crisis in 1960 which lead to SE Lets imagine a person who use to live in a village and who have constructed a hut for him to live. Definitely he should have face some problems in the beginning but was managed to build a hurt for him. Now if you ask him to construct another hut, he may be able to construct one more easily and in a better way. This new hut may be better than the first one and he may construct it in a relatively less time. But if you ask him to construct concrete and iron houses then ? Evolution is the name of the game in IT industry  In most of the cases that software which was tried to be build using those old tools and techniques were not complete.  Most of the times it was delivered too late.  Most of the projects were over-budgeted.  And in most of the case systems build using these techniques were not reliable – meaning that they were not be able to do what they were expected to do.  This lead to realization that only coding is not enough

Software Engineering-I Shahbaz Ahmed 27 What is a software process model? A simplified representation of a software process, presented from a specific perspective Examples of process perspectives: Workflow perspective represents inputs, outputs and dependencies Data-flow perspective represents data transformation activities Role/action perspective represents the roles/activities of the people involved in software process Generic process models Waterfall Evolutionary development Formal transformation Integration from reusable components

Software Engineering-I Shahbaz Ahmed 28 The costs of software engineering? Roughly 60% of costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs Costs vary depending on the type of system being developed and the requirements of system attributes such as performance and system reliability Distribution of costs depends on the development model that is used

Software Engineering-I Shahbaz Ahmed 29 Product development costs

Software Engineering-I Shahbaz Ahmed 30 What is CASE ? (Computer-Aided Software Engineering) Upper-CASE Tools to support the early process activities of requirements and design Lower-CASE Tools to support later activities such as programming, debugging and testing Software systems which are intended to provide automated support for software process activities, such as requirements analysis, system modelling, debugging and testing

Software Engineering-I Shahbaz Ahmed 31 What are the attributes of good software? The software should deliver the required functionality and performance to the user and should be maintainable, dependable and acceptable. Maintainability Software must evolve to meet changing needs; Dependability Software must be trustworthy; Efficiency Software should not make wasteful use of system resources; Acceptability Software must accepted by the users for which it was designed. This means it must be understandable, usable and compatible with other systems.

Software Engineering-I Shahbaz Ahmed 32 What are the key challenges facing software engineering? Heterogeneity, delivery and trust. Heterogeneity Developing techniques for building software that can cope with heterogeneous platforms and execution environments; Delivery Developing techniques that lead to faster delivery of software; Trust Developing techniques that demonstrate that software can be trusted by its users.

Software Engineering-I Shahbaz Ahmed 33 What are the key challenges facing software engineering? Software engineering in the 21 st century faces three key challenges: Legacy systems Old, valuable systems must be maintained and updated Heterogeneity Systems are distributed and include a mix of hardware and software Delivery There is increasing pressure for faster delivery of software

Software Engineering-I Shahbaz Ahmed 34 Professional and ethical responsibility of s/w engineers Software engineering involves wider responsibilities than simply the application of technical skills. Software engineers must behave in an honest and ethically responsible way if they are to be respected as professionals. Ethical behaviour is more than simply upholding the law.

Software Engineering-I Shahbaz Ahmed 35 Issues of professional responsibility Confidentiality Engineers should normally respect the confidentiality of their employers or clients irrespective of whether or not a formal confidentiality agreement has been signed. Competence Engineers should not misrepresent their level of competence. They should not knowingly accept work which is outwith their competence.

Software Engineering-I Shahbaz Ahmed 36 Issues of professional responsibility Intellectual property rights Engineers should be aware of local laws governing the use of intellectual property such as patents, copyright, etc. They should be careful to ensure that the intellectual property of employers and clients is protected. Computer misuse Software engineers should not use their technical skills to misuse other people’s computers. Computer misuse ranges from relatively trivial (game playing on an employer’s machine, say) to extremely serious (dissemination of viruses).

Software Engineering-I Shahbaz Ahmed 37 Some General Discussion that will demonize Software Engineering in your hearts

Software Engineering-I Shahbaz Ahmed 38 Can you develop this ?

Software Engineering-I Shahbaz Ahmed 39 Requirements Software Limitations of Non-engineered Software

Software Engineering-I Shahbaz Ahmed 40 Software Production has a Poor Track Record Example: Space Shuttle Software Cost: $10 Billion, millions of dollars more than planned Time: 3 years late Quality: First launch of Columbia was cancelled because of a synchronization problem with the Shuttle's 5 onboard computers. Error was traced back to a change made 2 years earlier when a programmer changed a delay factor in an interrupt handler from 50 to 80 milliseconds. The likelihood of the error was small enough, that the error caused no harm during thousands of hours of testing. Substantial errors still exist. Astronauts are supplied with a book of known software problems "Program Notes and Waivers".

Software Engineering-I Shahbaz Ahmed 41 Quality of today’s software…. The average software product released on the market is not error free.

Software Engineering-I Shahbaz Ahmed 42 Software Engineering: A Problem Solving Activity Analysis: Understand the nature of the problem and break the problem into pieces Synthesis: Put the pieces together into a large structure For problem solving we use Techniques (methods): Formal procedures for producing results using some well-defined notation Methodologies: Collection of techniques applied across software development and unified by a philosophical approach Tools: Instrument or automated systems to accomplish a technique

Software Engineering-I Shahbaz Ahmed Software Engineering: Definition Software Engineering is a collection of techniques, methodologies and tools that help with the production of a high quality software system with a given budget before a given deadline while change occurs.

Software Engineering-I Shahbaz Ahmed 44 Scientist vs Engineer Computer Scientist Proves theorems about algorithms, designs languages, defines knowledge representation schemes Has infinite time… Engineer Develops a solution for an application-specific problem for a client Uses computers & languages, tools, techniques and methods Software Engineer Works in multiple application domains Has only 3 months... …while changes occurs in requirements and available technology

Software Engineering-I Shahbaz Ahmed 45 Factors affecting the quality of a software system Complexity: The system is so complex that no single programmer can understand it anymore The introduction of one bug fix causes another bug Change: The “Entropy” of a software system increases with each change: Each implemented change erodes the structure of the system which makes the next change even more expensive (“Second Law of Software Dynamics”). As time goes on, the cost to implement a change will be too high, and the system will then be unable to support its intended task. This is true of all systems, independent of their application domain or technological base.

Software Engineering-I Shahbaz Ahmed 46 Why are software systems so complex? The problem domain is difficult The development process is very difficult to manage Software offers extreme flexibility Software is a discrete system Continuous systems have no hidden surprises (Parnas) Discrete systems have!

Software Engineering-I Shahbaz Ahmed 47 Dealing with Complexity 1. Abstraction 2. Decomposition 3. Hierarchy

Software Engineering-I Shahbaz Ahmed 48 What is this?

Software Engineering-I Shahbaz Ahmed Abstraction Inherent human limitation to deal with complexity The phenomena Chunking: Group collection of objects Ignore unessential details: => Models

Software Engineering-I Shahbaz Ahmed 50 Models are used to provide abstractions System Model: Object Model: What is the structure of the system? What are the objects and how are they related? Functional model: What are the functions of the system? How is data flowing through the system? Dynamic model: How does the system react to external events? How is the event flow in the system ? Task Model: PERT Chart: What are the dependencies between the tasks? Schedule: How can this be done within the time limit? Org Chart: What are the roles in the project or organization? Issues Model: What are the open and closed issues? What constraints were posed by the client? What resolutions were made?

Software Engineering-I Shahbaz Ahmed 51 Interdependencies of the Models System Model (Structure, Functionality, Dynamic Behavior) Issue Model (Proposals, Arguments, Resolutions) Task Model (Organization, Activities Schedule)

Software Engineering-I Shahbaz Ahmed 52 The “Bermuda Triangle” of Modeling System Models Issue Model Task Models PERT Chart Gantt Chart Org Chart Constraints Issues Proposals Arguments Object Model Functional Model Dynamic Model class... Code Pro Con Forward Engineering Reverse Engineering

Software Engineering-I Shahbaz Ahmed 53 Example of an Issue: Galileo vs the Church What is the center of the Universe? Church: The earth is the center of the universe. Why? Aristotle says so. Galileo: The sun is the center of the universe. Why? Copernicus says so. Also, the Jupiter’s moons rotate round Jupiter, not around Earth.

Software Engineering-I Shahbaz Ahmed 54 Issue-Modeling Issue: What is the Center of the Universe? Proposal1: The earth! Proposal2: The sun ! Pro: Copernicus says so. Pro: Aristotle says so. Pro: Change will disturb the people. Con: Jupiter’s moons rotate around Jupiter, not around Earth. Resolution (1615): The church decides proposal 1 is right Resolution (1998): The church declares proposal 1 was wrong

Software Engineering-I Shahbaz Ahmed Decomposition A technique used to master complexity (“divide and conquer”) Functional decomposition The system is decomposed into modules Each module is a major processing step (function) in the application domain Modules can be decomposed into smaller modules Object-oriented decomposition The system is decomposed into classes (“objects”) Each class is a major abstraction in the application domain Classes can be decomposed into smaller classes

Software Engineering-I Shahbaz Ahmed 56 Functional Decomposition Top Level functions Level 1 functions Level 2 functions Machine Instructions System Function Load R10 Add R1, R10 Read Input Transform Produce Output Transform Produce Output Read Input

Software Engineering-I Shahbaz Ahmed 57 Functional Decomposition Functionality is spread all over the system Maintainer must understand the whole system to make a single change to the system Consequence: Codes are hard to understand Code that is complex and impossible to maintain User interface is often awkward and non-intuitive Example: Microsoft Powerpoint’s Autoshapes

Software Engineering-I Shahbaz Ahmed 58 Autoshape Functional Decomposition: Autoshape Draw Rectangle Draw Oval Draw Circle Draw Change Mouse click Change Rectangle Change Oval Change Circle

Software Engineering-I Shahbaz Ahmed 59 What is This?

Software Engineering-I Shahbaz Ahmed 60 Model of an Eskimo Eskimo Size Dress() Smile() Sleep() Shoe Size Color Type Wear() * Coat Size Color Type Wear()

Software Engineering-I Shahbaz Ahmed 61 Iterative Modeling then leads to.... Eskimo Size Dress() Smile() Sleep() Cave Lighting Enter() Leave() lives in but is it the right model? Entrance * Outside Temperature Light Season Hunt() Organize() moves around Windhole Diameter MainEntrance Size

Software Engineering-I Shahbaz Ahmed 62 Alternative Model: The Head of an Indian Indian Hair Dress() Smile() Sleep() Mouth NrOfTeeths Size open() speak() * Ear Size listen() Face Nose smile() close_eye()

Software Engineering-I Shahbaz Ahmed 63 Class Identification Class identification is crucial to object-oriented modeling Basic assumption: 1. We can find the classes for a new software system: We call this Greenfield Engineering 2. We can identify the classes in an existing system: We call this Reengineering 3. We can create a class-based interface to any system: We call this Interface Engineering Why can we do this? Philosophy, science, experimental evidence What are the limitations? Depending on the purpose of the system different objects might be found How can we identify the purpose of a system?

Software Engineering-I Shahbaz Ahmed 64 What is this Thing?

Software Engineering-I Shahbaz Ahmed 65 Modeling a Briefcase BriefCase Capacity: Integer Weight: Integer Open() Close() Carry()

Software Engineering-I Shahbaz Ahmed 66 A new Use for a Briefcase BriefCase Capacity: Integer Weight: Integer Open() Close() Carry() SitOnIt()

Software Engineering-I Shahbaz Ahmed 67 Questions Why did we model the thing as “Briefcase”? Why did we not model it as a chair? What do we do if the SitOnIt() operation is the most frequently used operation? The briefcase is only used for sitting on it. It is never opened nor closed. Is it a “Chair”or a “Briefcase”? How long shall we live with our modeling mistake?

Software Engineering-I Shahbaz Ahmed Hierarchy We got abstractions and decomposition This leads us to chunks (classes, objects) which we view with object model Another way to deal with complexity is to provide simple relationships between the chunks One of the most important relationships is hierarchy 2 important hierarchies "Part of" hierarchy "Is-kind-of" hierarchy

Software Engineering-I Shahbaz Ahmed 69 Part of Hierarchy Computer I/O Devices CPU Memory Cache ALU Program Counter

Software Engineering-I Shahbaz Ahmed 70 Is-Kind-of Hierarchy (Taxonomy) Cell Muscle Cell Blood Cell Nerve Cell Striate Smooth RedWhite Cortical Pyramidal

Software Engineering-I Shahbaz Ahmed 71 So where are we right now? Three ways to deal with complexity: Abstraction Decomposition Hierarchy Object-oriented decomposition is a good methodology Unfortunately, depending on the purpose of the system, different objects can be found How can we do it right? Many different possibilities Our current approach: Start with a description of the functionality (Use case model), then proceed to the object model This leads us to the software lifecycle

Software Engineering-I Shahbaz Ahmed 72 Software Lifecycle Activities Subsystems Structured By class... Source Code Implemented By Solution Domain Objects Realized By System Design Object Design Implemen- tation Testing Application Domain Objects Expressed in Terms Of Test Cases ? Verified By class.... ? Requirements Elicitation Use Case Model Analysis...and their models

Software Engineering-I Shahbaz Ahmed 73 Software Lifecycle Definition Software lifecycle: Set of activities and their relationships to each other to support the development of a software system Typical Lifecycle questions: Which activities should I select for the software project? What are the dependencies between activities? How should I schedule the activities?

Software Engineering-I Shahbaz Ahmed 74 Reusability A good software design solves a specific problem but is general enough to address future problems (for example, changing requirements) Experts do not solve every problem from first principles They reuse solutions that have worked for them in the past Goal for the software engineer: Design the software to be reusable across application domains and designs How? Use design patterns and frameworks whenever possible

Software Engineering-I Shahbaz Ahmed 75 And oh yes one more thing Always remember the law of diminishing returns. “Your tea will get sweater up to a certain level only and the excess sugar will produce no effect” Same is the case with software engineering Moral Efficient resource Utilization

Software Engineering-I Shahbaz Ahmed 76 Key points Software engineering is an engineering discipline that is concerned with all aspects of software production. Software products consist of developed programs and associated documentation. Essential product attributes are maintainability, dependability, efficiency and usability. The software process consists of activities that are involved in developing software products. Basic activities are software specification, development, validation and evolution. Methods are organised ways of producing software. They include suggestions for the process to be followed, the notations to be used, rules governing the system descriptions which are produced and design guidelines.

Software Engineering-I Shahbaz Ahmed 77 Key points CASE tools are software systems which are designed to support routine activities in the software process such as editing design diagrams, checking diagram consistency and keeping track of program tests which have been run. Software engineers have responsibilities to the engineering profession and society. They should not simply be concerned with technical issues. Professional societies publish codes of conduct which set out the standards of behaviour expected of their members.