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Informatics 43 Introduction to Software Engineering

Informatics 43 Introduction to Software Engineering

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Informatics 43 Introduction to Software Engineering

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  1. Informatics 43Introduction to Software Engineering Lecture 6 Duplication of course material for any commercial purpose without the explicit written permission of the professor is prohibited.

  2. Today’s Lecture • Reminders • Requirements engineering • Requirements specification (documentation) • Requirements engineering with Use Cases

  3. Reminder: Fundamental Principles • Rigor and formality • Separation of concerns • Modularity • Abstraction • Anticipation of change • Generality • Incrementality These principles apply to all aspects of software engineering

  4. Reminder: High Cost

  5. Cost of Change Progressively Higher

  6. Why Requirements? • “[We] have grown to care about requirements because we have seen more projects stumble or fail as a result of poor requirements than for any other reason” • (Kulak and Guiney, in “Use Cases: Requirements in Context”) • Studies show that many of the key contributors to project failures originate or relate to requirements • (The Standish Group CHAOS reports)

  7. Some stats… • From those CHAOS reports • 31% of projects cancelled before they are even completed • Many others not delivered or not used (“shelfware”) even if completed • Many billions wasted per year on cancelled, unused or unusable projects • 52.7% of projects were more than 189% over budget when delivered • Requirements defects are expensive • They represent more than 70% of rework costs • Rework consumes about 30-50% of total project budget • Lack of user input/user involvement listed as most frequent problem

  8. Waterfall Requirements phase Changed requirements Verify Verify Specification phase Verify Design phase Verify Implementation phase Test Integration phase Development Maintenance Test Operations mode Retirement

  9. Waterfall Requirements phase Changed requirements Verify Verify Specification phase Verify Design phase Verify Implementation phase Test Integration phase Development Maintenance Test Operations mode Retirement

  10. The RUP Model In an iteration, you walk through all workflows Phases Process Workflows Inception Elaboration Construction Transition Business Modeling Requirements Analysis & Design Implementation Test Deployment Supporting Workflows Configuration Mgmt Workflows group activities logically Management Environment Preliminary Iteration(s) Iter.#1 Iter.#2 Iter.#n Iter.#n+1 Iter.#n+2 Iter.#m Iter.#m+1 Iterations

  11. Requirements Phase • Terminology • Requirements analysis/engineering • Activity of discovering/observing/gathering customer’s needs • Requirements specification • Activity of describing/documenting customer’s needs • Note: requirements address what a customer needs, not what a customer wants • A customer often does not know what they want, • let alone what they actually need… • Time-lag between initial desire and future need • Long and arduous, often educational, process • And things change “under our feet” during the requirements process...

  12. Requirements Analysis • System engineering versus software engineering • What role does software play within the full solution? • Trend: software is everywhere • Contract model versus participatory design • Contract: carefully specify requirements, then contract out the development • Participatory: customers, users, and software development staff work together throughout the life cycle

  13. Techniques for Requirements Analysis • Interview customer • Create use cases/scenarios • Prototype solutions • Observe customer • Identify important objects/roles/functions • Perform research • Construct glossaries • Question yourself Discuss: Is this familiar?

  14. Requirements Specification • Serves as the fundamental reference point between customer and software producer • Defines capabilities to be provided without saying how they should be provided • Defines the “what” • Does not define the “how” • Defines environmental requirements on the software to guide the implementers • Platforms, implementation language(s), … • Defines constraints on the software • Performance, usability, … • Defines software qualities

  15. Why Spend a Lot of Time? • A requirements specification is the source for all future steps in the software life cycle • Lays the basis for a mutual understanding • Consumer (what they get) • Software producer (what they build) • Identifies fundamental assumptions • Potential basis for future contracts • Better get it right • Upon delivery, some software is actually rejected by customers • Changes are cheap • Better make them now rather than later

  16. Users of a Requirements Document

  17. Non-Functional Requirement Types

  18. Document Structure • Introduction • Executive summary • Application context • Functional requirements • Environmental requirements • Software qualities • Other requirements • Time schedule • Potential risks • Future changes • Glossary • Reference documents

  19. Introduction • What is this document about? • Who was it created for? • Who created it? • Outline

  20. Executive Summary • Short, succinct, concise, to-the-point, description • Usually no more than one page • Identifies main goals • Identifies key features • Identifies key risks/obstacles

  21. Application Context • Describes the situation in which the software will be used • How will the situation change as a result of introducing the software? • “World Model” • Identifies all things that the system affects • Objects, processes, other software, hardware, and people • Provides an abstraction for each of those, characterizing the properties and behaviors that are relevant to the software system • Identifies fundamental assumptions

  22. Functional Requirements • Identifies all concepts, functions, features, and information that the system provides to its users • Provides an abstraction for each of those, characterizing the properties and functions that are relevant to the user • What is the system supposed to do? • What information does the system need? • What is supposed to happen when something goes wrong? An approximate user interface is part of functional requirements

  23. Environmental Requirements • Platforms • Hardware • Operating systems, types of machines, memory size, hard disk space • Software • Is it a Web app? Web 2.0?? • Is it open source? Linux? Apache? PHP/MySQL? • Is it enterprise software? .Net? Enterprise Java, J2EE? • Programming language(s) • Standards

  24. Desired Software “ilities” (Qualities) Correctness Reliability Efficiency Integrity Usability Maintainability Testability Flexibility Portability Reusability Interoperability

  25. Other Requirements • What about cost? • What about documentation? • What about manuals? • What about tutorials? • What about on-the-job training? • What about requirements that do not fit in any of the previous categories?

  26. Time Schedule • By when should all of this be done? • Initial delivery date • Acceptance period • Final delivery date • What are some important milestones to be reached? • Architectural design completed • Module design completed • Implementation completed • Testing completed

  27. Potential Risks • Any project faces risks • Boehm’s top ten risks (see lecture 3) • It is important to identify those risks up-front so the customer and you (!) are aware of them • One of the requirements could be to explicitly address the risks

  28. Future Changes • Any project faces changes over time • It is important to identify those changes up-front so the customer and you (!) are aware of them • These changes could simply pertain to potential future enhancements to the product • One of the requirements could be to build the product such that it can accommodate future changes • Note: structure the requirements document in such a way that it easily absorbs changes • Define concepts once • Partition separate concerns • …

  29. Glossary • Precise definitions of terms used throughout the requirements document

  30. Reference Documents • Pointers to existing processes and tools used within an organization • Pointers to other, existing software that provides similar functionality • Pointers to literature

  31. Observations • Document is structured to address the fundamental principles • Rigor • Separation of concerns • Modularity • Abstraction • Anticipation of change • Generality • Incrementality • Not every project requires every section of the document

  32. Specification Methods • Natural language • Data flow diagrams • Office automation • Finite state machines • Telephone systems • Coin-operated machines • Petri nets • Production plants • Formulas • Matrix inversion package • Objects (in object-oriented methods) • Use cases (in UML)

  33. Verification • Is the requirements specification complete? • Is each of the requirements understandable? • Is each of the requirements unambiguous? • Are any of the requirements in conflict? • Can each of the requirements be verified? • Are are all terms and concepts defined? • Is the requirements specification unbiased?

  34. Acceptance Test Plan • Accompanies a requirements specification • Specifies, in an operational way, consistency between the requirements specification and the system that will be delivered • Binds a customer to accept the delivered system if it passes all the tests • Covers all aspects of the requirements specification

  35. V-Model of Development and Testing Develop Requirements Execute System Tests Requirements Review Develop Acceptance Tests Acceptance Test Review Design Execute Integration Tests Design Review Develop Integration Tests Integration Tests Review Code Execute Unit Tests Code Review Develop Unit Tests Unit Tests Review

  36. Example • French fries and mayonnaise place