Applied Systems Analysis Fall 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 [email protected] 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. 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? MIS 375 • Read Assigned Chapters • Attendance required 10% 10% – Attendance required at the beginning and end of class • Project – Requirements Doc group – System Analysis Doc group – Design Doc and presentation • UML Homework Assignments • UML In class Exercises 40% 10% 20% 10% 30% 10% No Computer Usage During a Lecture Self Motivated Students will Likely Receive an “A” 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 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 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. • Why OO? 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 -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 LBVDS WLD-1 DD-21 V15 Direct expression •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 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 Faster Development Increased quality less re-work More Re use Easier maintenance Better Human Cognition Reduced Risk 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 $ Savings $ & Customer Satisfaction Customer -> Systems Analysis. -> Software What do I want? Customer • What will the system do? How do I test the •Define the Requirements (Analyze) Requirements? • How will the system do it? •Decompose the system (Design) • Assure the best solution (Analyze - Trade offs) Test Use Cases Systems Analysis Specialty Requirements •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 Specialty Engineering Software / Hardware Engineering How do I Implement the requirements? In a Nutshell (modified from Rosenberg) Dynamic Use Case Model Each Use case becomes Multiple Scenarios Which are detailed in 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 OO Process Steps Define requirements Allocate and Derive requirements Map requirements to use cases Map requirements to classes Define use cases Draw Diagrams Write use case summary Include requirements & External Interfaces Define domain model class diagram Add attributes when known Review requirements Define use case scenarios Include a summary Define first level decomposition class diagram Take from domain class diagram Include boundary objects, controllers and entities Review Preliminary Design Create a sequence diagram for each scenario Use only objects in the class diagram Update scenario documentation to include details Update class diagram Add methods to classes when known (Internal interfaces) Update Documentation (interfaces etc.) Review Design R Requirements 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. Misconceptions Requirements Analysis High Level Design Detailed Design Requirements are done first, then we do design. Manufacture H/W Code S/W Integration and Test If you believe this, I have a bridge I’d like to sell you #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 … Effect of Requirements Definition on Program Costs – Werner Gruhl NASA If you have not done a good job on requirements, you will encounter a large # of changes and the associated cost overruns Poor Assumptions: •Everyone knows how to write requirements •Requirements will take care of themselves •The Review process will fix all problems Proper Assumptions: Requirements cost •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 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. Problems with Requirements • Lack of Management Interest – Everyone knows how to write Requirements • Lack of Know how – A Requirement is: • Necessary • Attainable • Testable • 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 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….. 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 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 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 Is Each Requirement Clearly Written • Single Thought • Concise • Simple sentences – One subject one verb one object • Stand-alone • Unambiguous • What not How • • Forcing a design that is not needed Forcing a design does not meet the needs Example: ‘shall provide a Data base’ Ugly and clear is better than Ask yourself - Why? Because: beautiful and ambiguous •I need traceability between requirement levels Example: ‘ shall be stowed while underway’ •I need to add capability to add •This is an operational requirement not a system attributes to requirements requirements Should be: ‘shall provide a stowage environment’ •I need to be able to sort the requirements •I need to be able to filter the The system shall provide … requirements The system shall be capable of … The Data Base becomes a program element which has requirements associated with it. The system shall weigh … The xyz subsystem shall provide … use acronyms What Kinds of Requirements Are There? •Contractual •Management •Regulatory •Environmental •Technical •Operational – – – – – – – – – – – – – – 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 Any particular requirement may be more than one type. Requirement Database Types All Requirements are defined in the requirements database as one and only one of the following types: Ø Ø Ø Ø Ø Ø Ø Ø Ø Functional “… shall automatically track airborne targets…” Performance “…shall discriminate targets within 3 minutes…” Capacity “…shall maintain 300 tracks in the …” Constraint including cost, specific equipment, legacy components etc. Reliability “ MTBF shall be 100 days” Interface “ … shall use RS-232 interface to … “ Test “… the system test shall stress the system …” Safety “ “in accordance with SPCL-610 and BI-431 Data “…shall depict target range in meters…” We should do this but we don’t. It helps place the requirement in the proper section. 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 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. 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 Requirements are Linked • To higher level requirements derived and allocated – Flow down • To use cases > Test cases • To objects • To analyses Linkage Example A derived requirement results from analysis of a higher level requirement. Original Requirement Analysis Derived 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. 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 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? 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. 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. 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. 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. 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) 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 Student Requirement Exercise 2 • Requirement: [AAA05350] The external markings shall be in accordance with the customer's requirements. • Problems – – • Better Student Requirement Exercise 3 • Requirement: [SAF00200] Specify interlocks, shielding, safety guards, barriers, and warning markings where a personnel hazard can exist. • Problems – – • Better 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 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 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 Student Requirement Exercise 7 • Requirement: [SAF00870] Delicate equipment shall be located where it will not be damaged during maintenance. • Problems – – • Better Student Requirement Exercise 8 • Requirement: [SAF01060] New/modified air distribution and outlets shall be designed to minimize noise levels. • Problems – – • Better 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 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 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 Student Requirement Exercise 12 • Requirement: [AAAA1080] A suitable means shall be provided for extraction and conversion of the recorded data to a format that, when using existing equipment, will readily permit analysis by ground facilities. • Problems – – • Better Student Requirement Exercise 13 • Requirement: [AAAA0630] Assuming the radar target is identifiable to the operator and the position of the radar target is accurately known, then the radar contribution to aircraft position accuracy shall be less than 125 feet +/-10% plus the target position error (CEP) at 5 nm from 300 feet above ground level (AGL). • Problems – – • Better Student Requirement Exercise 14 • Requirement: [AAAA0047] The Mission Computer shall issue an ACAWS message if unsafe ramp and cargo door operation is attempted. • Problems – – • Better Student Requirement Exercise 15 • Requirement: [RMS00940] This concept shall be such that minor repair and check out of the modules may be accomplished at the intermediate maintenance level with the more extensive repair and check out accomplished at depot level maintenance. • Problems – – • Better Student Requirement Exercise 16 • Requirement: [RMS00340] Module retention techniques shall be carefully designed to integrate the insertion mechanism, required connector insertion force, thermal contact area, and extraction mechanism. Heretofore, conventional electronics have required the same considerations, but to a lesser degree because of their more conventional housings. • Problems – – • Better Student Requirement Exercise 17 • Requirement: [AAA05510] It shall be possible to inspect the hardware from time to time for unauthorized modifications. To this end, hardware construction will be as simple and as standard as possible. • Problems – – • Better Student Requirement Exercise 18 • Requirement: [AAA05190] The C-130J Aircraft System shall be designed and constructed to minimize electromagnetic interference and propagation from the subsystems in accordance with Mil-Std 1818. • Problems – – • Better Student Requirement Exercise 19 • Requirement: [SDA00020] Minimum utilization of strategic materials shall be observed in development of the airplane. Specified materials shall be given preference over proprietary items and shall conform to applicable specifications. • Problems – – • Better Student Requirement Exercise 20 • Requirement: [AAA05720] The equipment will be as small and as light as is practical and shall be capable of being easily handled. • Problems – – • Better Homework 1 (by next week) • Read – Whitten Chap 1 & 3 – Answer 5 questions per chapter (see following page) – Come with questions • Write requirements for your perfect spouse – At least 20 requirements – For each requirement, define the verification type. (test, analyze, demonstrate, inspect) – Keep it polite • • • • • • • • • • • • • • • • • • • Chap 1 Define information system and name seven types of information system applications. Define stakeholder and Identify different types of stakeholders who use or develop information systems, give examples of each. Define the unique role of systems analysts in the development of information systems. Identify those skills needed to successfully function as an information system analyst. Describe current business drivers that influence information systems development. Describe current technology drivers that influence information systems development. Briefly describe a simple process for developing information systems. Differentiate between the waterfall and the iterative/incremental approaches to systems development. Chap 3 Describe the motivation for a system development process in terms of the Capability Maturity Model (CMM) for quality management. Differentiate between the system life cycle and a system development methodology. Describe 10 basic principles of system development. Define problems, opportunities, and directives—the triggers for systems development projects. Describe the PIECES framework for categorizing problems, opportunities, and directives. Describe the essential phases of system development. For each phase, describe its purpose, inputs, and outputs. Describe cross life cycle activities that overlap multiple system development phases. Describe typical alternative “routes” through the basic phases of system development. Describe how routes may be combined or customized for different projects. Describe various automated tools for system development.