CS 5150 Software Engineering Lecture 10 Requirements 3

CS 5150 Software Engineering Lecture 10 Requirements 3 CS 5150 1

Course Administration Test 2 Monday October 3, Philips Hall 101 at 7: 30 p. m. Covers all material in Lectures 1 to 11. Presentations Sign up with Corinne Russell for your presentations. She will be out next week. Please copy Raghu and me on messages about the presentations. CS 5150 2

Course Administration Assignment 2, Milestone 2, October 12 -14 Read information on the Assignments Web page i Client(s) 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 Report due Friday at 11: 00 p. m. iv Survey due Friday at 11: 00 p. m. CS 5150 3

Course Administration Assignment 2, Milestone 2, October 12 -14 • One third of the total work from the feasibility study. • If you are following an iterative or incremental process, this is a major milestone when you report visible progress to your client. This will include at least a first set of requirements, and design, including user interface design. It might be the end of the first iteration or sprint. • If you are following a modified waterfall process, this milestone should include completion of the requirements phase and perhaps the first steps in the design. Include a review of progress to date against your plan. CS 5150 4

Software Development Principles and Practices 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 CS 5150 5

Modeling Techniques for Requirements Analysis and Specification The craft of requirements analysis, modeling and specification is to select the appropriate tool for the particular task. • A variety of tools and techniques. • Many familiar from other courses. • No correct technique that fits all situations. As you build understanding of the requirements through viewpoint analysis, scenarios and use cases, etc. , use models to specify requirements. The models provide a bridge between the client's understanding and the developers. CS 5150 6

Modeling Tools: 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 CS 5150 7

Modeling Tools: Data-Flow Model Example: University Admissions (first attempt) Rejection Application Completed form Receive application Evaluate application Applicant Acceptance Shows the flow, but where is the data stored? CS 5150 8

Modeling Tools: Data-Flow Model Example: Assemble Application Stage Acknowledgment Application form Receive Applicant Supporting information Pending database CS 5150 Completed application Acknowledgment AND Begin evaluation Does this model cover all applications? Are there special cases? 9 Evaluation request AND Applicant database

Modeling Tools: Data-Flow Model Example: Process Completed Application Stage The requirements will need specification of the decisionmaking process. Evaluation request Rejection Evaluation Acceptance Special request Applicant database CS 5150 10 Financial aid Offer

Modeling Tools: Decision Table University Admission Decision SAT > S T F F F GPA > G - T F F Athletics code = - - T T F F Recommendations > A- - - T F X X X Send rejection letter Send acceptance letter X X X Note that the rules are specific and testable. CS 5150 11

Modeling Tools: Flowchart An informal modeling technique to show the decisions and paths that data takes through a system. Operation Decision Manual operation Report CS 5150 12

Modeling Tools: Flowchart Example: University Admissions Form received New F applicant? T New database record Update database Application T complete? F Notify student CS 5150 13 Evaluate

Modeling Tools: 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() CS 5150 14

Modeling Tools: 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 1 S 1 0 CS 5150 0 1 S 3 S 2 0 1 15

Modeling Tools: Finite State Machine Example: Therapy Control Consol Example: Radiation Therapy Control Console You are developing requirements for the operator's control console. In an interview, the client describes the procedures that the operator must follow when operating the machine. 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. CS 5150 16

Modeling Tools: Finite State Machine 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. " CS 5150 17

Modeling Tools: Finite State Machine State Transition Diagram Discuss each state and transition with the client. Select field Enter Patients Enter Fields Start (lock off) Setup Beam on Ready Stop (lock on) Select patient CS 5150 18

Modeling Tools: Finite State Machine State Transition Table Select Enter lock off Start Patient Field Patients Fields Patients Setup Patients Fields Ready Patients Fields Stop lock on Fields Setup Ready Beam on Setup Beam Ready Setup on This table can be used for requirements definition, program design, and acceptance testing. CS 5150 19

Transition Diagram for User Interfaces Example: CS 5150 Web Site (part) home syllabus projects slides books concepts tests assignintegrity about ments examples surveys scripts CS 5150 20

Modeling Tools: 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) Entity-relationship models can be used both for requirements specification and for the design specification. CS 5150 21

Modeling Tools: Entity-Relation Diagram An entity (noun) A relation between entities (verb) An entity or relation attribute Note: There are various notations used for entity-relationship diagrams. This is the notation used by Chen (1976). CS 5150 22

Modeling Tools: Entity Relationship Diagram Example: CS 5150 Project Is. Client Major 1 1 CS 5150 Student Project 1 5 to 7 0: n Is. Contact Is. Member CS 5150 Client team member 23 1

Entity Relationship Diagram as a Design Tool Example: Database Schema for Web Data Notation: Each table represents an entity Each arrow represents a relation CS 5150 24

Modeling Tools: Petri Nets A Petri Net models parallelism A Event S Event 1 S A Event n Event 1 A Event n CS 5150 . . . S 1 Sm 25

Modeling Tools: 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 CS 5150 26

Requirements Definition: 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 developed, the data dictionary in the requirements is the basis of the system data dictionary, which is part of the system specification. CS 5150 27

A Note on Class and Object Models This course teaches class and object models as a tool for design. Some people recommend class and 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 are equally useful for requirements. * CS 5150 28