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Requirements Engineering

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Presentation on theme: "Requirements Engineering"— Presentation transcript:

1 Requirements Engineering
(Part 2)

2 Objectives Identify guidelines of creating requirements analysis models. Explain structured and object-oriented analysis approaches to requirements modelling. Identify three classifications of modelling elements based on object-oriented approach. Introduce use case diagram, activity diagram, class diagram, state diagram, and sequence diagram. Badariah Solemon 2010

3 Overview Activity Action Task Communication Project Inception
Requirements Engineering Req. Elicitation Req. Analysis & Negotiation Req. Specification Req. Verification and Validation Req. Management Planning Modeling Requirements Modeling Design Modeling Context Modeling Technical Modeling Construction Deployment Badariah Solemon 2010

4 Requirements/Analysis Model
A graphical representations 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 Design Model Analysis Model Badariah Solemon 2010

5 Rules of Thumb Suggested by Arlow and Neustadt in Pressman (2009):
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 non-functional models until design. 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 Badariah Solemon 2010

6 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. 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 task should move from essential information toward implementation detail. *Recap from chapter 4 Badariah Solemon 2010

7 Domain Analysis According to Donald Firesmith in Pressman (2009):
“ 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 . . .” Badariah Solemon 2010

8 What is Domain Analysis? 900724
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. Badariah Solemon 2010

9 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 decision-makers Technical (detailed-level) modeling * Module 4 Badariah Solemon 2010

10 Approaches for Technical Modeling
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 Object-oriented Analysis model objects, classes, and the relationships and behavior associated with them. The industry standard for the OO modeling is known as Unified Modelling Language (UML) specification and 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, and etc. * Relate with generic modeling elements in Part 1. Badariah Solemon 2010

11 Flow-oriented Modeling
According to Pressman (2009): 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 Badariah Solemon 2010

12 OO Analysis Approach Need to first understand OO concepts, which include objects, classes, attributes, methods, sub-class, super-class, and etc. Classifications of OO modeling elements (Pressman, 2005): Scenario-based to show how end-users interact with the system e.g.: use-case diagram, activity diagram, swim-lane diagram Badariah Solemon 2010

13 OO Analysis Approach (cnt’d)
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. Badariah Solemon 2010

14 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. Badariah Solemon 2010

15 Scenario-based Modeling: Use Case (cnt’d)
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 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. Badariah Solemon 2010

16 Use Case: Example #1 Pressman (2009): Use case diagram for SafeHome System Badariah Solemon 2010

17 Airline Reservation System
Use Case: Example #2 Airline Reservation System Check In Passenger Add New Reservation Cancel Reservation Airline Reservation System Badariah Solemon 2010

18 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. For example, in the Airline Reservation System, the ‘Add New Reservation’ use case uses ‘Check Space Availability’ and ‘Record Passenger Information’ 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. For example, 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. Badariah Solemon 2010

19 Relationships of Use Cases: Example #1
Airline Reservation System Check In Passenger Add New Reservation Cancel Reservation Weigh Luggage Assign Seat Check Seat Availability Record Passenger Information Assign Window Seat Assign Aisle Seat Badariah Solemon 2010

20 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 the how those activities depend on one another. 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. Badariah Solemon 2010

21 Activity Diagram: Example #1
Pressman (2009), pp 162 Badariah Solemon 2010

22 Scenario-based Modeling: Swimlane Diagram
A variation of activity diagram. To represent the flow of activities described by the use-case 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. Badariah Solemon 2010

23 Swimlane: Example #1 Pressman (2009), pp 163 Badariah Solemon 2010

24 Swimlane: Example #2 (
Badariah Solemon 2010

25 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). Badariah Solemon 2010

26 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, , and ContactNumber. Student perform operations such as RegisterCourse, DropCourse, and PrintTranscript. Student StudentID Firstname Lastname ContactNumber RegisterCourse() DropCourse() PrintTranscript() Name of class List of attributes List of methods Badariah Solemon 2010

27 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 in any way You may need to analyse further this relationship by identifying multiplicity of the association because there is possibility that a students might register for none, one, or several courses. Among the potential multiplicity indicators: (next page) There exist other types of associations such as association class, aggregation (basic and composition), reflexive associations, and realisation. For further explanation, refer to OMG (2009). Badariah Solemon 2010

28 Class Diagram: with Several Classes (cnt’d)
Indicator Meaning 0..1 Zero or one 1 One only 0..* Zero or more 1..* One or more N Only n (where n > 1) 0..n Zero to n (where n > 1) 1..n One to n (where n > 1) Example: Registered 0..* attended by Course CourseCode CourseName CreditHours Fees Student StudentID Firstname Lastname ContactNumber RegisterCourse() DropCourse() PrintTranscript() Badariah Solemon 2010

29 Class Diagram: with Several Classes (cnt’d)
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. Badariah Solemon 2010

30 Class Diagram: with Several Classes (cnt’d)
Postgraduate ProjectTitle ThesisSubmitDate Postgraduate ProjectTitle ThesisSubmitDate Postgraduate ProjectTitle ThesisSubmitDate Class Diagram: with Several Classes (cnt’d) Example: * ATM Case Study Course CourseCode CourseName CreditHours Fees Student StudentID Firstname Lastname ContactNumber RegisterCourse() DropCourse() PrintTranscript() Postgraduate ProjectTitle ThesisSubmitDate Undergraduate CreditLimit Registered 0..* attended by Badariah Solemon 2010

31 Class Diagram: Example
Postgraduate ProjectTitle ThesisSubmitDate Postgraduate ProjectTitle ThesisSubmitDate Postgraduate ProjectTitle ThesisSubmitDate Class Diagram: Example Models a customer order from a retail catalog ( Badariah Solemon 2010

32 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 Badariah Solemon 2010

33 The States of a System State —a set of observable circum-stances 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 Badariah Solemon 2010

34 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 Badariah Solemon 2010

35 State Diagram: Example #1
Badariah Solemon 2010

36 Statechart Diagram: Example #2
State Diagram for the ControlPanel Class (Pressman, 2009) Badariah Solemon 2010

37 Behavioral Modeling: Sequence Diagram
An interaction diagram that details how operations are carried out -- what messages are sent and when. Are organized according to time. The 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. Badariah Solemon 2010

38 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 Badariah Solemon 2010

39 Sequence Diagram: Example #1
Pressman (2009) Badariah Solemon 2010

40 Sequence Diagram: Example #2
A sequence diagram for making a hotel reservation Badariah Solemon 2010

41 Summary You have been introduced to:
Guidelines of creating requirements analysis models. Two approaches to requirements modelling: structured and object-oriented analysis approaches. Three classifications of modelling elements based on object-oriented approach. Overview of several OO modeling elements such as use case diagram, activity diagram, class diagram, state diagram, and sequence diagram. Badariah Solemon 2010

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