1 CS 501 Spring 2003 CS 501: Software Engineering Lecture 11 Requirements III

2 CS 501 Spring 2003 Course Administration Collect Quiz 2 after class. Also uncollected Quiz 1 First Presentations and Report Read instructions on Web site Everybody must make at least one presentation during the semester Remember to schedule your presentations

3 CS 501 Spring 2003 Techniques for Requirements Analysis and Definition A variety of tools and techniques. Many are familiar from other courses. There is no correct technique that fits all situations. The craft of requirements analysis and specification is to select the appropriate tool for the particular task.

4 CS 501 Spring 2003 Bad Example: Decision Table University Admission Decision Note that the rules are vague. High SATTFFFFF High grades-TFFFF Sports--TTFF Recommendations--TFTF RejectXXX AcceptXXX

5 CS 501 Spring 2003 Good Example: Decision Table University Admission Decision Note that the rules are now specific and testable. SAT > STFFFFF GPA > G-TFFFF Athletics code =  --TTFF Recommendations > A---TFTF Send rejection letterXXX Send acceptance letterXXX

6 CS 501 Spring 2003 Data-Flow Models External entities Processing steps Data stores or sources Data flows

7 CS 501 Spring 2003 Data-Flow Example: University Admissions Applicant Application form Receive application Completed application Evaluate Rejection Acceptance

8 CS 501 Spring 2003 Data-Flow Example: Assemble Application Stage Applicant Application form Receive Completed application Supporting information Pending database Acknowledgment Initiate evaluation Applicant database Evaluation request AND Acknowledgment

9 CS 501 Spring 2003 Data-Flow Example: Process Completed Application Stage Rejection Evaluation Applicant database Evaluation request Acceptance Financial aid Offer Special request

10 CS 501 Spring 2003 Procedural Models: Flowchart Operation Decision Manual operation Report

11 CS 501 Spring 2003 Flowchart: University Admissions Form received New? Database record T Notify student FUpdate database Complete? Notify student T F Evaluate

12 CS 501 Spring 2003 Procedural Models: Pseudo-code 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) max_team then error (bad_team) if error() = none then comments = read_report (report) return (comments (text), comments (grade)) else return error()

13 CS 501 Spring 2003 Entity-Relation Model A 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

14 CS 501 Spring 2003 Entity-Relation Diagram An entity A relation between entities An entity or relation attribute An inheritance relation

15 CS 501 Spring 2003 Example: CS 501 Project Student CS501 Student Major Project 5 to 7 1 Member of Person Client 1 Tech contact 0:n

16 CS 501 Spring 2003 Example: MARC Catalog Record Caroline R. Arms, editor, Campus strategies for libraries and electronic information. Bedford, MA: Digital Press, 1990.

17 CS 501 Spring 2003 MARC Format for Books r Campus strategies for libraries and electronic information 260 {Bedford, Mass.} : Digital Press, c Academic libraries--United States--Automation. 650 Libraries and electronic publishing--United States. 700 Arms, Caroline R. (Caroline Ruth)

18 CS 501 Spring 2003 Entity-Relation Diagram for MARC Book Short title Catalog record Describes Control numb Subject heading Is about Creator Editor of Author of 1:n 1 0:n

19 CS 501 Spring 2003 Data Dictionaries A data dictionary is a list of names used by the system Brief definition (e.g., what is "date") What is it (e.g., number, 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.

20 CS 501 Spring 2003 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.

21 CS 501 Spring 2003 Transition Diagrams A system is modeled as a set of states, S i 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 (S i, Cj) = S k Example S1S1 S2S2 S3S

22 CS 501 Spring 2003 Finite State Machine Example: Therapy control console [informal description]

23 CS 501 Spring 2003 State Transition Diagram Patients Fields SetupReady Beam on Enter Start Stop Select field Select patient (interlock) (ok)

24 CS 501 Spring 2003 State Transition Table Select Patient Select Field Enter ok StartStop interlock Patients Fields Setup Ready Beam on Fields Patients Setup Ready Beam on Ready

25 CS 501 Spring 2003 Petri Nets A Petri Net models parallelism A S1S1 SmSm S S A Event 1 Event n Event A Event 1 Event n.. f(A; E) S f(A; E 1,..,E n ) S f(A; E 1,..,E n ) S 1,..,S m

26 CS 501 Spring 2003 Prototyping Requirements Rapid prototyping: A method for specifying requirements by building a system that demonstrates the functionality of the required system