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05 fse requirementsengineering
 

05 fse requirementsengineering

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    05 fse requirementsengineering 05 fse requirementsengineering Presentation Transcript

    • B. Computer Science (SE) (Hons.) CSEB233: Fundamentals of Software Engineering Requirements Engineering: Modeling
    • Objectives  Identify guidelines of creating requirements analysis models  Explain structured and object-oriented analysis approaches to requirements modeling  Identify three classifications of modeling elements based on object-oriented approach  Apply use case diagram, activity diagram, class diagram, state diagram, and sequence diagram
    • Overview Activity Action Communication Task Project Inception Requirements Engineering Req. Elicitation Req. Analysis & Negotiation Req. Specification Req. Verification and Validation Req. Management Requirements Modeling Design Modeling Context Modeling Technical Modeling Planning Modeling Construction Deployment
    • Requirements Engineering: Modeling Guidelines of Creating Requirements Analysis/Models
    • Requirements/Analysis Model  A graphical representation of  business processes,  the problems to be solved, and  the new proposed product (software)  Objectives  To describe software requirements  To establish a basis for the creation of a software design  To define a set of requirements that can be validated once the software is built  Bridges the gap between a software specification and a software design Software specification Analysis Model Design Model
    • Rules of Thumb  Suggested by Arlow and Neustadt:  The model should focus on requirements that are visible within the problem or business domain  The level of abstraction should be relatively high Each element of the analysis model should add to an overall understanding of software requirements and provide insight into the information domain, function and behavior of the system  Delay consideration of infrastructure and other nonfunctional models until design 
    • Rules of Thumb  Suggested by Arlow and Neustadt:  Minimize coupling throughout the system  Be sure that the analysis model provides value to all stakeholders  Keep the model as simple as possible especially if extra diagrams do not provide new information
    • Requirements Modeling Principles  Principle #1:  The information domain of a problem must be represented and understood  Principle #2:  The functions that the software performs must be defined  Principle #3:  The behavior of the software, as a consequence of external events, must be represented
    • Requirements Modeling Principles  Principle #4:  The models that depict information, function, and behavior must be partitioned in a manner that uncovers detail in a layered (or hierarchical) fashion.  Principle #5:  The analysis of task should move from essential information toward implementation detail
    • Requirements Engineering: Modeling Structured and Object-oriented Analysis Approaches
    • What is Domain Analysis?  According to Donald Firesmith:  “Software domain analysis is the identification, analysis, and specification of common requirements from a specific application domain, typically for reuse on multiple projects within that application domain . .”  [Object-oriented domain analysis is] the identification, analysis, and specification of common, reusable capabilities within a specific application domain, in terms of common objects, classes, subassemblies, and frameworks . . .”
    • What is Domain Analysis?  An on-going SE activity that is not connected to any software project (by domain analyst)  Involves: Defining the domain to be investigated  Collecting a representative sample of applications in the domain  Analyzing each application in the sample  Developing an analysis model for the objects 
    • Requirements Analysis Modeling  Categorized into two main levels of details:  Context (conceptual-level) modeling*  High-level conceptual descriptions of a product and its environment.  Must be supplemented with detailed-level models, e.g.: architectural model  Usually usable to non-technical people and decisionmakers  Technical (detailed-level) modeling
    • Technical Modeling Approaches  Structured Analysis  Considers data and the processes that transform the data as separate entities.  Includes data models, data flow models and behavioral models  e.g., ERD, DFD, state machine model
    • Technical Modeling Approaches  Object-oriented Analysis  model objects, classes, and the relationships and behavior associated with them  The industry standard for OO modeling is the Unified Modeling Language (UML) specification  The current available version is 2.2 (OMG, 2009).  e.g., use-case diagrams, activity diagrams (swim-lane diagram), sequence diagram, class diagram, state diagram, etc.
    • Requirements Engineering: Modeling Classifications of Modeling Elements
    • Flow-oriented Modeling  Represents how data objects are transformed as they move through the system  Data flow diagram (DFD) is the diagrammatic form that is used  Considered by many to be an “old school” approach, but continues to provide a view of the system that is unique  It should be used to supplement other analysis model elements
    • OO Analysis Approach  Need to first understand OO concepts, which include objects, classes, attributes, methods, subclass, super-class, etc.  Classifications of OO modeling elements:  Scenario-based  to show how end-users interact with the system  e.g., use-case diagram, activity diagram, swimlane diagram
    • OO Analysis Approach  Class-based  to specify classes and objects, attributes, operations, and associations and dependencies  e.g., class diagram, class responsibility collaborator (CRC) model, collaboration diagram  Behavioral  to model how the system reacts to external event  e.g., event-driven use-case, state diagram, sequence diagram
    • 1. Scenario-based Modeling Use Case  Ivar Jacobson:  “[Use-cases] are simply an aid to defining what exists outside the system (actors) and what should be performed by the system (use-cases)”  Elements:  Actor  a „stick figure‟ that represent roles of people, other system (database, servers, and legacy systems) or equipment that interact with use cases in the system.
    • 1. Scenario-based Modeling Use Case  Use case  an oval shape labeled with the use case name (inside or outside the oval) that represent a complete unit of system functionality  A use case may be made up of a set of scenario  Each scenario describes the steps that consist of an interaction between the actors and the system  Just like DFDs, you can continue to add detail by breaking the uses cases into more use cases
    • Use Case Example 1  Use case diagram for SafeHome System Saf eHome Access camera surveillance via t he Int ernet Conf igure Saf eHome syst em paramet ers homeowner Set alarm cameras
    • Use Case Example 2  Airline Reservation System Airline Reservation System Check In Passenger Ticket Clerk Add New Reservation Cancel Reservation
    • Relationships of Use Cases  Uses  An arrow drawn from use case A to use case B to indicate that in the process of completing functionality A, functionality B will be performed too  e.g.,, in the Airline Reservation System, the „Add New Reservation‟ use case uses „Check Space Availability‟ and „Record Passenger Information‟ use cases
    • Relationships of Use Cases  Extends  An arrow drawn from use case A to use case B to indicate that the use case A is a special way of doing use case B and must be done to complete use case B  e.g., in the Airline Reservation System, there are two ways to assign a seat either by assigning a window seat or by assigning an aisle seat
    • Relationships of Use Cases Example 1 Airline Reservation System «uses» Weigh Luggage «extends» «uses» Assign Window Seat «extends» Check In Passenger Assign Seat «uses» Assign Aisle Seat «uses» Ticket Clerk Add New Reservation Cancel Reservation Check Seat Availability Record Passenger Information
    • 1. Scenario-based Modeling Activity Diagram  Supplements the use case by providing a graphical representation of the flow of interaction within a specific scenario  Activity diagrams and statechart diagrams are related   While a statechart diagram focuses attention on an object undergoing a process (or on a process as an object), an activity diagram focuses on the flow of activities involved in a single process The activity diagram shows how those activities depend on one another
    • 1. Scenario-based Modeling Activity Diagram  UML‟s basic symbols: Symbol Purpose To represent an activity To represent a flow To represent branching decisions To indicate all parallel activities within the system.
    • Activity Diagram Example 1 ent er password and user ID valid passwor ds/ ID invalid passwor ds/ ID selec t major f unc t ion prompt f or reent ry ot her f unct ions m ay also be select ed input t r ies r em ain selec t surv eillanc e no input t r ies r em ain t hum bnail views select a specif ic cam er a selec t spec if ic c amera - t humbnails selec t c amera ic on v iew c amera out put in labelled window prompt f or anot her v iew exit t his f unct ion see anot her cam er a
    • 1. Scenario-based Modeling Swimlane Diagram  A variation of activity diagram  Represents the flow of activities described by the usecase, and  At the same time, indicate which actor (if there are multiple actors involved in a specific use-case) or analysis class has responsibility for the action described by an activity rectangle
    • Swimlane Example 1 homeowner c a m e ra i n t e rf a c e ent er password and user ID valid p asswo r d s/ ID in valid p asswo r d s/ ID select m ajor f unct ion o t h er f u n ct io n s m ay also b e prom pt f or reent ry select ed in p u t t r ies select surveillance r em ain n o in p u t t r ies r em ain t h u m b n ail views select a sp ecif ic cam er a select specif ic cam era - t hum bnails select cam era icon generat e video out put view cam era out put in labelled window prom pt f or anot her view exit t h is f u n ct io n see an o t h er cam er a
    • (http://edn.embarcadero.com/article/31863 Swimlane Example 2
    • 2. Class-based Modeling Class Diagram  Depicts a collection of system‟s classes, their attributes, and the relationships between the classes  A class is an object applicable to a system You can think of an object as any person, thing, place, concept, event, and etc.  Objects have attributes (information stored about and object or variables for OO programming) and methods or operations (things an object perform) 
    • Class Diagram Example 1  To model a class, use a rectangle with three sections:    name of the class (top) list of attributes (middle) methods (bottom).  Example:  a Student class which has attributes  StudentID, Firstname, Lastname, Email, and ContactNumber.  Student perform operations such as RegisterCourse, DropCourse, and PrintTranscript. Student StudentID Firstname Lastname Email ContactNumber RegisterCourse() DropCourse() PrintTranscript() Name of class List of attributes List of methods
    • Class Diagram With Several Classes  Need to show how they are related to each other  Two basic types of relationships between classes:  Associations  This relationship exists when two classes are related to each other  Analyze this relationship further by identifying multiplicity of the association because there is possibility that a student might register for none, one, or several courses  Some potential multiplicity indicators: (see next slide)  There are other types of associations such as association class, aggregation (basic and composition), reflexive associations, and realization.  For further explanation, refer to OMG (2009).
    • Class Diagram With Several Classes  Example: Student StudentID Firstname Lastname Email ContactNumber RegisterCourse() DropCourse() PrintTranscript() Indicator 0..1 1 0..* 1..* N 0..n 1..n Meaning Zero or one One only Zero or more One or more Only n (where n > 1) Zero to n (where n > 1) One to n (where n > 1) 0..* attended by Registered 0..* Course CourseCode CourseName CreditHours Fees
    • Class Diagram With Several Classes  Inheritance/Generalisation  Different classes usually share the same attributes and/or methods  To avoid repeating the same attributes and/or methods, you need to take advantage of the inheritance (also known as generalisation) mechanism  When class X inherits from class Y, you may say that X is the subclass of Y and Y is the superclass of X  UML‟s notation for inheritance is a line with upward arrowhead pointing from the subclass to the superclass
    • Class Diagram With Several Classes  Example Student StudentID Firstname Lastname Email ContactNumber RegisterCourse() DropCourse() PrintTranscript() Undergraduate CreditLimit 0..* Registered Course attended by 0..* CourseCode CourseName CreditHours Fees Postgraduate ProjectTitle ThesisSubmitDate
    • Class Diagram: Example  Models a customer order from a retail catalog  (http://edn.embarcadero.com/article/31863)
    • 2. Class-based Modeling CRC  CRC modeling provides a simple means for identifying and organizing the classes that are relevant to system or product requirements (Wir, 1990)  A CRC model is really a collection of standard index cards that represent classes    The cards are divided into three sections Along the top of the card you write the name of the class In the body of the card you list the class responsibilities on the left and the collaborators on the right (Ambler, 1995)
    • CRC: Example Class: Class: Descrip tion: Class: Descrip tion: FloorPlan Class: Descrip tion: Responsibility: Descrip tion: Responsibility: Responsibility: Responsibility: Collaborator: Collaborator: Collaborator: Collaborator: defines floor plan name/type manages floor plan positio ning scales f lo or plan for display scales f lo or plan for display incorporates w alls , doors and w indow s Wall show s position of video cameras Camera
    • 3. Behavioral Modeling  Make a list of the different states of a system  How does the system behave?  Indicate how the system makes a transition from one state to another  How does the system change state?  indicate event  indicate action  Draw a state diagram, also known as statechart diagram or a sequence diagram
    • The States of a System  State  a set of observable circumstances that characterizes the behavior of a system at a given time  State transition  the movement from one state to another  Event  an occurrence that causes the system to exhibit some predictable form of behavior  Action  process that occurs as a consequence of making a transition
    • State Representations  In the context of behavioral modeling, two different characterizations of states must be considered the state of each class as the system performs its function and  the state of the system as observed from the outside as the system performs its function 
    • State Representations  The state of a class takes on both passive and active characteristics A passive state is simply the current status of all of an object‟s attributes  The active state of an object indicates the current status of the object as it undergoes a continuing transformation or processing 
    • State Diagram  Notations:  States are rounded rectangles  Transitions are arrows from one state to another  Events or conditions that trigger transitions are written beside the arrows  The initial state (black circle) is a dummy to start the action  Final states (2 circles with inner black circle) are also dummy states that terminate the action  The action that occurs as a result of an event or condition is expressed in the form/action  e.g., Cancel/Quit
    • State Diagram Example 1  http://edn.embarcadero.com/article/31863
    • Statechart Diagram Example 1  State Diagram for the ControlPanel Class t imer < lockedTime t imer > lockedTime locked password = incorrect & numberOfTries < maxTries comparing reading numberOfTries > maxTries key hit password ent ered do: validat ePassw ord password = correct select ing act iv at ion successful
    • 3. Behavioral Modeling Sequence Diagram  An interaction diagram that show how operations are carried out - what messages are sent and when  Are organized according to time  Time progresses as you go down the page  The objects involved in the operation are listed from left to right according to when they take part in the message sequence
    • Sequence Diagram  Each vertical dotted line is a lifeline, representing the time that an object exists  Each arrow is a message call  An arrow goes from the sender to the top of the activation bar of the message on the receiver's lifeline  The activation bar represents the duration of execution of the message  The diagram has a clarifying note, which is text inside a dog-eared rectangle
    • Sequence Diagram Example 1 co nt rol panel homeowner syst em ready A sensors sensors syst em readin g password ent ered request lookup comparing result password = correct request act ivat ion num berOf Tries > m axTries locked A t imer > lockedTime select ing act ivat ion successful act ivat ion successful Figure 8 .2 7 Sequence diagram (part ial) f or Saf eHome securit y f unct ion
    • Sequence Diagram Example 2  A sequence diagram for making a hotel reservation  http://edn.embarcadero.com/article/31863
    • Summary  You have been introduced to:  Guidelines of creating requirements analysis models.  Two approaches to requirements modeling  structured  object-oriented analysis Three classifications of modeling elements based on object-oriented approach  Several OO modeling elements such as use case diagram, activity diagram, class diagram, state diagram, and sequence diagram 
    • THE END Copyright © 2013 Mohd. Sharifuddin Ahmad, PhD College of Information Technology