CS 501: Software Engineering

1. CS 501: Software Engineering Lecture 9 Requirements 3

2. Course Administration Feasibility Study Everybody should have receive comments. Teaching Assistants have been assigned. Remember to send your weekly reports. Quiz 1 Uncollected answer books are at the reception at 301 College Avenue.

3. Discussion of Feasibility Study General Who will read the feasibility study? What is needed to decide to go ahead? Scope and understanding of project Statement of the task Preliminary requirements and technical analysis Deliverables and business considerations Confidence Outline plan. Does it inspire confidence? Visibility plan.  How will progress be reported?  Risk analysis. How are the risks to be minimized?

4. Course Administration Assignment 2, First Milestone, March 6-8 Read information on the Assignments Web page Reserve time for your presentation. See the home page of the Web site. i Client must be present ii Not all team members must be present, but each team member must make a presentation at least once during the semester iii Try to find a time when the TA can be present

5. Course Administration Assignment 2, First Milestone, March 6-8 • One third of the total work from the feasibility study. • If you are following an iterative process, this is a major milestone when you can report visible progress to your client. Typically, this will include a first set of requirements, a provisional design and a prototype that can be used to demonstrate the functionality of the system, including user interface design. • If you are following a modified waterfall process, this progress report should include completion of the requirements phase and perhaps the first steps in the design.

6. Software Development Principles and Practices Software development Software development is a craft. Software developers have a variety of tools that can be applied in different situations. Part of the art of software development is to select the appropriate tool for a given implementation

7. Modeling Techniques for Requirements Analysis and Definition The craft of requirements analysis and specification is to select the appropriate tool for the particular task. • A variety of tools and techniques. • Many are familiar from other courses. • There is no correct technique that fits all situations. As you build understanding of the requirements through scenarios and use cases, use modeling tools to specify requirements. The models provide a bridge between the client's understanding and the developers.

8. Decision Table: Bad Example University Admission Decision High SAT T F F F F F High grades - T F F F F Sports - - T T F F Recommendations - - T F T F Reject X X X Accept X X X Note that the rules are too vague.

9. Decision Table: Good Example University Admission Decision SAT > S T F F F F F GPA > G - T F F F F Athletics code =  - - T T F F Recommendations > A- - - T F T F Send rejection letter X X X Send acceptance letter X X X Note that the rules are now specific and testable.

10. Data-Flow Models An informal modeling technique to show the flow of data through a system. External entities Processing steps Data stores or sources Data flows

11. Data-Flow Example: University Admissions (first try) Rejection Application form Completed application Receive application Evaluate Applicant Acceptance Shows the flow, but where is the data stored?

12. Data-Flow Example: Assemble Application Stage Acknowledgment Acknowledgment Application form Completed application AND Evaluation request Begin evaluation Receive Applicant AND Does this model cover all applications? Are there special cases? Supporting information Applicant database Pending database

13. Data-Flow Example:Process Completed Application Stage The data-flow diagram will need specification of the decision-making process. Rejection Evaluation request Acceptance Offer Financial aid Evaluation Special request Applicant database

14. Procedural Models: Flowchart An informal modeling technique to show the decisions and paths that data takes through a system. Operation Decision Manual operation Report

15. Form received Database record Update database Flowchart: University Admissions F T New? Complete? F T Evaluate Notify student Notify student

16. Procedural Models: Pseudo-code An informal modeling technique to show the logic behind part of a system. Example: Check project plan check_plan (report) if report (date_time) > due_date_time then error (too_late) if report (client) = none then error (no_client) if report (team) < min_team or> max_team then error (bad_team) if error() = none then comments = read_report (report) return (comments (text), comments (grade)) else return error()

17. Transition Diagrams A system is modeled as a set of states, Si A transition is a change from one state to another. The occurrence of a condition, Ci, causes the transition from one state to another Transition function: f (Si, Cj) = Sk Example 0 S1 S2 1 0 1 0 S3 1

18. Transition Diagram for CS 501 Web Site home assign-ments syllabus books projects integrity about quizzes exam-ples slides surveys concepts

19. Therapy Control Consol: Finite State Machine Example: Radiation Therapy Control Console You are developing requirements for the operator's control console. In a client interview, the client describes the dangers inherent in using the machine. The operator must follow a strict procedure before the machine is ready to run. You use a finite state machine to specify the procedures. This shows the client that you understand the requirements and specifies the procedures for the developers.

20. Therapy Control Consol: Scenario "The set up is carried out before the patient is made ready. The operator selects the patient information from a database. This provides a list of radiation fields that are approved for this patient. The operator selects the first field. This completes the set up. "The patient is now made ready. The lock is taken off the machine and the doses with this field are applied. The operator then returns to the field selection and chooses another field."

21. State Transition Diagram Discuss each state and transition with the client. Select field Start Enter Enter (lock off) Beam on Patients Fields Setup Ready Stop (lock on) Select patient

22. Therapy Control Consol: State Transition Table Select Patient Select Field lock on lock off Enter Start Stop Patients Fields Setup Patients Fields Setup Fields Ready Patients Beam on Patients Ready Fields Setup Beam on Ready Setup

23. Entity-Relation Model A requirements and design methodology for relational databases • A database of entities and relations • Tools for displaying and manipulating entity-relation diagrams • Tools for manipulating the database (e.g., as input to database design) Warning: There is much confusion about definitions and notation

24. Entity-Relation Diagram An entity A relation between entities An entity or relation attribute An inheritance relation

25. CS501 Student Example: CS 501 Project Major Client 0:1 1:n Student Client team member Project 0:n 0:1 1 Tech contact 5 to 7 Member of

26. Example: Schema for Web Data CS 501 Spring 2005

27. Part of an Entity-Relation Diagram for a Book Catalog 0:n Book Author of 0:n 1 0:n Creator Editor of 0:n Describes 1 0:n Catalog record Subject heading 1:n Is about Short title Control numb

28. Data Dictionaries A data dictionary is a list of names used by the system • Name (e.g., "start_date") • Brief definition (e.g., what is "date") • What is it? (e.g., integer, relation) • Where is it used (e.g., source, used by, etc.) • May be combined with a glossary As the system is implemented, the data dictionary in the requirements is input to the system data dictionary, which is a formal part of the system specification.

29. Event 1 Event 1 A A Event n Event n Petri Nets A Petri Net models parallelism Event f(A; E) S A S f(A; E1,..,En) S S . S1 . f(A; E1,..,En) S1,..,Sm Sm

30. Prototyping Requirements Rapid prototyping is the most comprehensive of all modeling methods A method for specifying requirements by building a system that demonstrates the functionality of key parts of the required system Particularly valuable for user interfaces

31. A Note on Object Models This course teaches object models as a tool for design. Some people recommend object models for requirements definition, but it is difficult to use them without constraining the system design. Flow charts and finite state machines are supported by UML as design models, but can also be used for requirements. *