Applied Systems Analysis Fall 2005

1. Applied Systems AnalysisFall 2005 Class Notes 1 Douglas Low (315) 474 – 2774 (cell) 1 min question (315) 456-3372 (work) 2 min question (315) 703-6297 (home) 5 min question Email Douglas.a.low@lmco.com

2. Scope of Class • System/Software Development Process • Requirements • Analysis • Design • OO Analysis and Design using UML • How to develop use cases and associated artifacts • How and When to use What diagrams • What is and When to use OO vs. Functional • What is architecture? How to not abuse it. • Trade studies and feasibility analysis • Linkage of requirements to design and analysis classes • Useful during system sell off. You will analyze and design a practical system that will improve a real world situation.

3. Who the Heck is this Guy? • Douglas Low • MS in Computer science from SU • Been with GE/ Martin Marietta/ Lockheed Martin for 23 years. • Half in Software half in Systems engineering • RADAR and SONAR • Worked on OO extensively for DD-21 • From the beginning…Flailing… Formal courses… many Use cases • Working with the OOSESWWG at the Corporate level • Working with (not for) our local Process group to develop the OO process • SRS • Architecture Document Who the Heck are You? What do you want from me?

4. MIS 375 • Read Assigned Chapters 10% • Attendance required 10% • Attendance required at the beginning and end of class • Project 40% • Requirements Doc group 10% • System Analysis Doc group 20% • Design Doc and presentation 10% • UML Homework Assignments 30% • UML In class Exercises 10% No Computer Usage During a Lecture Self Motivated Students will Likely Receive an “A”

5. Development Process • Identify the problem (SOW) • Analyze the problem (System Requirements) • Design • Identify Alternate, candidate approaches to solve the problem • Design the chosen solution • Build • ..the chosen architecture pieces • Put the pieces together (integration) • Test • ..the parts • ..the system

6. What is UML? • Unified Modeling Language • Graphical Language • An attempt to combine notation from many analysis and design notations • Booch, Rumbaugh, Jacobson …… • Now is controlled by Object Management Group of which LM is a member. • Moving to UML 2 • Includes Codes from diagrams UML is a Language Not a Process

7. Objects – UML – Use cases • Object Oriented Software was invented by Xerox Parc in the 80’s. • Partitioned software into objects that owned its data and kept it private as much as possible. • Data hiding, data encapsulation were concepts that were fundamental to OO • Use Cases were invented by Ivar Jacobson in 1986 • Use case model describes the interaction of system with the outside world. • Describes the behavior or functionality of a system from the outside in. • “use case model is intended for communicating with customers and users” • “A special sequence of transactions performed by a user and a system in dialogue.” • UML – Unified Modeling Language • A visual language designed to construct, visualize and document artifacts of software systems • Incorporates several elements of three major diagramming notations into one language.

8. Why OO?

9. Benefits of OO • Maintenance and evolution of a system cause changes, but they are isolated to specific components, not the entire system. • Object-oriented concepts provide a framework for development according to effective systems and software engineering principles • Application of reusable components is facilitated and results in lower development costs across projects. • Object technology facilitates higher built-in quality, due to improved understandability, usability, maintainability, extensibility, modifiability, and reusability." • ACC LBVDS WLD-1 DD-21 V15 Direct expression Objects are natural metaphors for both physical objects and abstract entities. Expressing computations in terms of objects reduces the gap between concept and program. Malleability Good programs evolve. Evolution is easiest when the modifications are local. Objects combine data with functions to manipulate that data (allowing localization) and access to objects' data is restricted (enforcing localization). Extensibility Using inheritance, new objects and their behaviors can be defined as incremental modifications and extensions of existing objects. Abstraction Using polymorphism, similarities among objects can be expressed in the program, allowing us to write code in terms of the similarities without regard to the differences. COBOLREPORT.com • Faster Development • Increased Quality • Easier Maintenance • Enhances Modifiability • Easier reuse • System more resilient to change • Reduced development risks for complex systems due to integration spread out • Appeals to human cognition • Colorado University • -reduced time to market • greater product flexibility • schedule predictability • expressive power of OO • encourages reuse • resilience to change • reduced risk • appeals human cognition • Kåre Synnes Faster Development Increased quality less re-work More Re use Easier maintenance Better Human Cognition Reduced Risk $ Savings $ & Customer Satisfaction

10. Customer -> Systems Analysis. -> Software Use Cases Objects / Classes/ Use Cases Use Cases Tests Cases • Customer helps define system behavior with Use Cases • Use cases become Test cases for all levels of decomposition (System, Segment, CI) • Define requirements in terms of objects and Use Cases • What will the system do? • Define the Requirements (Analyze) • How will the system do it? • Decompose the system (Design) • Assure the best solution (Analyze - Trade offs) How do I test the Requirements? Test What do I want? Customer Systems Analysis Specialty Engineering Specialty Requirements Software / Hardware Engineering How do I Implement the requirements?

11. In a Nutshell (modified from Rosenberg) Dynamic Each Use case becomes Multiple Scenarios Which are detailed in Use Case Model Sequence Diagram Requirements get mapped to logical and physical components – just as they always did (Use cases & Classes) Static Becomes more Detailed And eventually Domain Model Class Diagram

12. OO Process Steps • Ø      Define requirements • Allocate and Derive requirements • Map requirements to use cases • Map requirements to classes • Ø      Define use cases • Draw Diagrams • Write use case summary • Include requirements & External Interfaces • Ø      Define domain model class diagram • Add attributes when known • ØReview requirements • Ø      Define use case scenarios • Include a summary • Ø      Define first level decomposition class diagram • Take from domain class diagram • Include boundary objects, controllers and entities • ØReview Preliminary Design • Ø     Create a sequence diagram for each scenario • Use only objects in the class diagram • Update scenario documentation to include details • Ø      Update class diagram • Add methods to classes when known (Internal interfaces) • Ø     Update Documentation (interfaces etc.) • Ø    Review Design R

13. Requirements

14. Requirements Are….. • Specific, demonstrate-able, statements that exactly specify what the system will do as well as a set of constraints that the system will operate under. • A contract with the customer • Usually have the word “shall” in it. For example: • The students shall do their homework. • If the students do not do their homework they shall be penalized. • Penalization for missing homework assignments shall be a zero entered for the homework assignment. • If a student “instant messages” during class they shall receive a zero for class attendance for that day.

15. Misconceptions Requirements Analysis High Level Design What Really Happens Detailed Design Manufacture H/W Code S/W If you believe this, I have a bridge I’d like to sell you Requirements are done first, then we do design. Integration and Test

16. #1 Problem with Requirements Requirements are not glamorous Architecture How Requirements What If you do a good job with requirements you will get NO credit Because Requirements are boring – However? • You Must Get Organized in order to assure: • Complete, Accurate, Doable …

17. Effect of Requirements Definition on Program Costs – Werner Gruhl NASA • Poor Assumptions: • Everyone knows how to write requirements • Requirements will take care of themselves • The Review process will fix all problems • Proper Assumptions: • Everyone does not know how to write good requirements • The requirements definition process is not well understood • The review process cannot fix all problems • Bad Requirements will be a major cost driver over the life of the program If you have not done a good job on requirements, you will encounter a large # of changes and the associated cost overruns Requirements cost

18. Types of Requirements Errors • Requirements drive: • complexity • cost • schedule • verification • operations • Provide contractual basis for verification and acceptance Having requirements in a set of books will not allow you to assure and quickly update requirements. Database is needed.

20. Problems with Requirements • Lack of Know how • A Requirement is: • Necessary • Attainable • Testable • Lack of Management Interest • Everyone knows how to write Requirements • Lack of Information leads to bad Assumptions • Required to write good requirements • Scope – needs, goals, constraints, budget, schedule • Missions • Operational Concept Can be Circumvented in a Program Plan

21. The Requirements process is not well understood • Requirements Process should be included in a well defined program plan • The owner of each requirement must Analyze: • Is it Necessary - Not a wish list • Prioritize & scrutinize • Maintain its lineage • Is it Verifiable - How will the requirement be tested? • Is it Achievable – Technical and Cost • If a question exists, place it on the risk plan • Is it Clearly written • Does the requirement apply to a single component? • Is it at the proper level (system, subsystem, element, component) • Coordinated effort with all stakeholders included e.g. Customer, Manufacturing, Specialty, Equipment eng, … Document assumptions, lineage, verifiability Raise issue to the program level – Cost Risk Assumptions…..

22. Is Each Requirement Necessary • Examine (and Document?) each Requirement • Assumptions • Why it is necessary • What is the cost impact • Prioritize the requirement • Maintain the lineage We should do more of this.

23. Is Each Requirement Achievable • Technical, Schedule and Cost Considerations • Get the facts right • Place in a risk pool until fully analyzed Remember 49% of requirement errors are due to incorrect facts

24. Is each Requirement Verifiable • Subjective requirements are not verifiable • Look for words like: Maximize, minimize, support, adequate, but not limited to, user friendly, easy, sufficient • Determine how each requirements will be verified as it is written • test, ‘shall be .3 seconds’ • demonstrate, ‘shall be capable of simultaneous viewing’ • analyze, ‘ MTBF shall be 1 day’ • Inspect, ‘shall be green’ Subjective Requirements from the customer must be converted into achievable and agreed to Requirements

25. Is Each Requirement Clearly Written • Stand-alone • Unambiguous • What not How • Forcing a design that is not needed • Forcing a design does not meet the needs • Single Thought • Concise • Simple sentences • One subject one verb one object • Example: ‘shall provide a Data base’ • Ask yourself - Why? Because: • I need traceability between requirement levels • I need to add capability to add attributes to requirements • I need to be able to sort the requirements • I need to be able to filter the requirements • The Data Base becomes a program element which has requirements associated with it. Ugly and clear is better than beautiful and ambiguous • Example: ‘ shall be stowed while underway’ • This is an operational requirement not a system requirements • Should be: ‘shall provide a stowage environment’ The system shall provide … The system shall be capable of … The system shall weigh … The xyz subsystem shall provide … use acronyms

26. What Kinds of Requirements Are There? • Functional • Performance • EMC/EMI • Safety • Security • Test • Packaging • Reliability • Portability • Schedule • Interface • COTS/NDI • Cost • Data • Training • GFE/CFE • Physical Characteristics • Design & Construction • Quality Assurance • Power/Grounding • Human Factors • Transportability • Maintainability • Supportability • Producibility • Availability • Disposal • Contractual • Management • Regulatory • Environmental • Technical • Operational Any particular requirement may be more than one type.

27. Requirement Database Types All Requirements are defined in the requirements database as one and only one of the following types: Ø      Functional “… shall automatically track airborne targets…” Ø      Performance “…shall discriminate targets within 3 minutes…” Ø      Capacity “…shall maintain 300 tracks in the …” Ø      Constraint including cost, specific equipment, legacy components etc. Ø      Reliability “ MTBF shall be 100 days” Ø      Interface “ … shall use RS-232 interface to … “ Ø      Test “… the system test shall stress the system …” Ø      Safety “ “in accordance with SPCL-610 and BI-431 Ø      Data “…shall depict target range in meters…” We should do this but we don’t. It helps place the requirement in the proper section.

28. Right and Wrong Terms • WRONG: The system shall support a training coordinator in defining scenarios • RIGHT: The system shall provide input screens for defining training scenarios. Or The system should support a training coordinator in defining scenarios Beware of: Maximize, minimize, support, adequate, but not limited to, user friendly, easy, sufficient Requirements Shall Facts Will Goals Should

29. Requirements Beget Requirements • Additional requirements are allocated or derived from the original set. • An allocated requirement is a system requirement that is allocated in whole or in part to subsystems, components, etc. Example 1: “All software shall be written in Ada.” • Direct Allocation:Allocated in whole to all software components. Example 2: “System MTBF shall be 100 hours.” • Apportioned:Subsystem MTBFs allocated via reliability analysis.

30. The top 10 Reasons for Not Doing Requirements 10. We don’t need requirements, we’re using objects/java/… 9. The users don’t know what they want 8.We already know what the users want 7.Who cares what the users want? 6. We don’t have time to do requirements 5. It’s too hard to do requirements 4. My boss frowns when I write requirements 3. The problem is too complex to write requirements 2. It’s easier to change the system later than to do requirements up front. 1. We have already started writing code, an we don’t want to spoil it. www.Volere.co.uk

31. Requirements are Linked • To higher level requirements derived and allocated • Flow down • To use cases > Test cases • To objects • To analyses

32. Linkage Example A derived requirement results from analysis of a higher level requirement. Examples: High level requirement: “Door when closed shall prevent outside air from entering the room at a rate greater than 10 cc per hour.” Derived requirement: “Tolerance between door and door frame shall be no greater than .1 inches.” • Linked to the original requirement and an analysis of the door leakage. Analysis Original Requirement Derived requirement

33. Summary – Make it Better • Program Plan – Goals, Objectives, Constraints, Missions, Operational Concept • Don’t start until you have these • Necessary, Verifiable, Achievable • The process includes tests for each of these • Treat each requirement as if it were a change • Accountability – Each requirement should have an owner • Owner should be willing to defend the need for each requirement Each Requirement should be treated as if it were going to affect the program Because it does

34. Improving Requirements, Case 1 • Requirement: “The pilot and/or co-pilot shall also be able to hear or see a visible or audible caution/warning signal in case of emergency, hazard, etc.” • Problems • Multiple requirements. (Pilot/co-pilot see/hear) • What emergency, hazard, etc. conditions? • Defining a solution with visible or audible warning? • What are pilot/co-pilot able to see/hear? • What do you verify? • Better • 1. The system shall provide a caution/warning signal to the pilot in case of emergency or hazard conditions defined in Appendix A. 2. Similar for co-pilot. • If we insist on specifying the type of signal: The system shall provide an X dB audible (Y micron visible) caution/warning signal to the pilot in case of emergency or hazard conditions defined in Appendix A. Similar for co-pilot. Signal duration?

35. Improving Requirements, Case 2 • Requirement: “The user shall be notified with a low battery warning lamp light when the voltage drops below 3.6 volts and the current workspace or input data shall be saved.” • Problems • Multiple requirements. (Notify and save) • Defining a solution with warning lamp light? • What do you verify? • Better • 1. The system shall provide a signal when the voltage drops below 3.6 volts. • 2. The system shall save the current workspace data when the voltage drops below 3.6 volts.

36. Improving Requirements, Case 3 • Requirement: “The crew shall always hear the smoke detector alarm when smoke is detected unless the alarm is being tested or suppressed.” • Problems • Subjective wishful thinking - “always hear” • Loophole for escape - “unless” • What do you verify? • Better • 1. The smoke detector shall provide an alarm to the crew when smoke is detected. • 2. The crew shall be able to suppress the smoke detector alarm when the detector is in the “Test” mode.

37. Improving Requirements, Case 4 • Requirement: “Provided that the designated input signals from the specified devices are received in the correct order where the system is able to differentiate the designators, the output signal shall comply with the required framework of section 4.4.5 to indicate the desired input state.” • Problems • Rambling long sentence • What do you verify? • Better • 1. The output signal shall comply with section 4.4.5. • 2. The output signal shall provide the input state.

38. Improving Requirements, Case 5 • Requirement: “The user shall be provided with a user-friendly front end for operating the system.” • Problems • Vague terminology • What do you verify? • Better • 1. The system shall provide menus and dialog boxes to aid the user in operating the system. Or, • 2. The system shall provide step-by-step instructions to guide users in starting operations.

39. Student Requirement Statement Exercises • Review, comment on, and improve the requirement statements on the following charts • Do these statements • Have the attributes of a “good” requirement? (Clear, complete, consistent, correct, feasible, objective, problematic, singular, succinct, verifiable) • Satisfy style tips for “good” requirements? (Simple sentence, correct grammar and spelling, avoids excess modifiers, avoids subjective language, required or desired, avoids abbreviations and acronyms, unique identifier, independent of outside text, free of loopholes)

40. Student Requirement Exercise 1 • Requirement: [AAA05520] It shall be possible to check that the software contains no unauthorized features. This will be done by manual means and by use of such automatic aids as may be available at the time. • Problems • Better

41. Student Requirement Exercise 2 • Requirement: [AAA05350] The external markings shall be in accordance with the customer's requirements. • Problems • Better

42. Student Requirement Exercise 3 • Requirement: [SAF00200] Specify interlocks, shielding, safety guards, barriers, and warning markings where a personnel hazard can exist. • Problems • Better

43. Student Requirement Exercise 4 • Requirement: [SAF00670] New equipment, modifications, rearrangements, or new interfaces for existing equipment shall be designed to ensure the level of safety of the present system is maintained. New systems will be designed with an absolute minimum of connections and terminations. • Problems • Better

44. Student Requirement Exercise 5 • Requirement: [SAF00330] All energized light indicators shall be legible when reviewed under actual or simulated bright sunlight conditions or under a blackout enclosure (including NVIS) and shall be easily readable by the aircrew. • Problems • Better

45. Student Requirement Exercise 6 • Requirement: [SAF00760] Equipment which retain high potential after it has been turned off shall be located where personnel cannot touch it and discharge circuits shall be provided to dissipate the charge in the shortest possible time after the equipment is turned off. • Problems • Better

46. Student Requirement Exercise 7 • Requirement: [SAF00870] Delicate equipment shall be located where it will not be damaged during maintenance. • Problems • Better

47. Student Requirement Exercise 8 • Requirement: [SAF01060] New/modified air distribution and outlets shall be designed to minimize noise levels. • Problems • Better

48. Student Requirement Exercise 9 • Requirement: [SAF01090] The cockpit sensing portion of the air conditioning temperature control system shall be located in the cockpit to provide optimum temperature for the greatest number of crew members. • Problems • Better

49. Student Requirement Exercise 10 • Requirement: [RMS00660] As a goal, single error correct/double error detect code shall be used in large bulk semiconductor memories. It should be considered in any application involving large amounts of semiconductor memory, but may impose unacceptable speed and complexity penalties in some applications (e.g., CPU). • Problems • Better

50. Student Requirement Exercise 11 • Requirement: [AAA04760] Safety critical equipment shall comply with the applicable performance standard when subjected to the specified lightning requirements. • Problems • Better