Systems Analysis ITEC 3155 The Object Oriented Approach

Systems Analysis – ITEC 3155 The Object Oriented Approach – Use Cases 7

7 Learning Objectives u What are use cases? u Use case diagrams u Use case and scenario descriptions Systems Analysis and Design in a Changing World, 4 th Edition 2

7 Overview u Objective of requirements definition is understanding users’ needs, business processes, and system to support business processes u Understand define requirements for a new system using object-oriented analysis models and techniques u Line between object-oriented analysis and objectoriented design is somewhat fuzzy l Iterative approach to development l Models built in analysis are refined during design Systems Analysis and Design in a Changing World, 4 th Edition 3

7 Object-Oriented Requirements u Object-oriented modeling notation is Unified Modeling Language (UML 2. 0) u UML was accepted by Object Management Group (OMG) as standard modeling technique u Purpose of Object Management Group l Promote theory and practice of object-oriented technology for development of distributed systems l Provide common architectural framework for OO Systems Analysis and Design in a Changing World, 4 th Edition 4

Object-Oriented Requirements (continued) 7 u Object-oriented system requirements are specified and documented through process of building models u Modeling process starts with identification of use cases and problem domain classes (things in users’ work environment) u Business events trigger elementary business processes (EBP) that the new system must address as use cases u Use cases define functional requirements Systems Analysis and Design in a Changing World, 4 th Edition 5

Object-Oriented Requirements Models u Use case diagrams – identify actors and their use u Use case descriptions – include details of a use case 7 cases (goals) and how actors use the system u Systems sequence diagrams (SSDs) – define inputs and outputs and sequence of interactions between user and system for a use case u Activity diagrams – describe user and system activities for a use case u State object machine diagrams – describe states of each Systems Analysis and Design in a Changing World, 4 th Edition 6

Requirements Models—Traditional versus OO 7 (Figure 7 -1) Systems Analysis and Design in a Changing World, 4 th Edition 7

The System Activities— A Use Case/Scenario View 7 u Use case analysis used to identify and define all business processes that system must support u Use case – an activity a system carried out, usually in response to a user request u Actor l Role played by user l Outside automation boundary Systems Analysis and Design in a Changing World, 4 th Edition 8

Techniques for Identifying Use Cases 7 (Review from Chapter 5) u Identify user goals l Each goal at the elementary business process (EBP) level is a use case l EBP – task performed by one user in one place and in response to business event that adds measurable business value, and leaves system and data in consistent state u Event decomposition technique (event table) u CRUD analysis technique (create, read/report, update, delete) to ensure coverage Systems Analysis and Design in a Changing World, 4 th Edition 9

7 Use Case Diagram u Graphical UML diagram that summarizes information about actors and use cases u Simple diagram shows overview of functional requirements u Can have multiple use case diagrams l By subsystem l By actor Systems Analysis and Design in a Changing World, 4 th Edition 10

7 Simple Use Case with an Actor (Figure 7 -2) Systems Analysis and Design in a Changing World, 4 th Edition 11

Use Case Diagram with Automation Boundary and Alternate Actor Notation (Figure 7 -3) Systems Analysis and Design in a Changing World, 4 th Edition 7 12

7 All Use Cases Involving Customer as Actor Systems Analysis and Design in a Changing World, 4 th Edition (Figure 7 -4) 13

7 Use Cases of RMO Order Entry Subsystem (Partial Figure 7 -5 with package symbol) Systems Analysis and Design in a Changing World, 4 th Edition 14

7 <<Includes>> Relationship u Documents situation in which one use case requires the services of a common subroutine u Another use case is developed for this common subroutine u. A common use can be reused by multiple use cases Systems Analysis and Design in a Changing World, 4 th Edition 15

Example of Order-Entry Subsystem with <<Includes>> Use Cases (Figure 7 -6) Systems Analysis and Design in a Changing World, 4 th Edition 7 16

CRUD Analysis for Identifying/Confirming Use Cases u CRUD 7 – create, read/report, update, delete u Information Engineering (IE) technique to identify event table or directly develop use case diagram u Compares identified use cases with domain model class diagram u Every class in class diagram must have use cases to support creating, reading, reporting, updating, and deleting object instances u Confirms system integration requirements Systems Analysis and Design in a Changing World, 4 th Edition 17

7 Use Case Description u Use case description provides details of preconditions, postconditions, sequence of activities, and exception conditions in use case u Describes actor interacting with computer system step-bystep to carry out business activity u May have several scenarios for a use case, each a specific use case instance u Three levels of detail: brief, intermediate, and fully developed description u Many analysts prefer to write narrative descriptions of use cases instead of drawing activity diagrams Systems Analysis and Design in a Changing World, 4 th Edition 18

Brief Description of Create New Order Use Case (Figure 7 -7) Systems Analysis and Design in a Changing World, 4 th Edition 7 19

Intermediate Description of the Telephone Order Scenario for Create New Order Use Case (Figure 7 -8) Systems Analysis and Design in a Changing World, 4 th Edition 7 20

Intermediate Description of the Web Order Scenario for Create New Order (Figure 7 -9) Systems Analysis and Design in a Changing World, 4 th Edition 7 21

7 Fully Developed Description of Telephone Order Scenario for Create New Order Use Case (Figure 7 -10) Systems Analysis and Design in a Changing World, 4 th Edition 22

Top Detail from Fully Developed Use Case Description (Figure 7 -10) Systems Analysis and Design in a Changing World, 4 th Edition 7 23

Middle Detail from Fully Developed Use Case Description (Figure 7 -10) Systems Analysis and Design in a Changing World, 4 th Edition 7 24

Bottom Detail from Fully Developed Use Case Description (Figure 7 -10) Systems Analysis and Design in a Changing World, 4 th Edition 7 25

7 Use Case Description Components u Use case name/scenario name u Actors/stakeholders u Related use cases u Preconditions – set of criteria that must be true prior to initiation of the use case u Postconditions – set of criteria that must be true upon completion of the use case u Flow of activities (steps in one column or two) u Exception conditions Systems Analysis and Design in a Changing World, 4 th Edition 26

7 Activity Diagrams u Used to document workflow of business process activities for each use case or scenario u Standard UML 2. 0 diagram as seen in Chapter 4 u Can support any level of use case description; a supplement to use case descriptions u Helpful in developing system sequence diagrams Systems Analysis and Design in a Changing World, 4 th Edition 27

7 Activity Diagram Symbols Systems Analysis and Design in a Changing World, 4 th Edition 28

Activity Diagram that Models a Workflow (Figure 413) Systems Analysis and Design in a Changing World, 4 th Edition 7 29

7 Activity Diagram— Telephone Order Scenario (Figure 7 -12) Systems Analysis and Design in a Changing World, 4 th Edition 30

7 Activity Diagram— Web Order Scenario (Figure 7 -13) Systems Analysis and Design in a Changing World, 4 th Edition 31

7 SSD Notation u Actor represented by a stick figure – a person (or role) that interacts with system by entering input data and receiving output data u Object is a rectangle with name of object underlined – shows individual object and not class of all similar objects ( : System for SSD ) u Lifeline or object lifeline is a vertical line under object or actor to show passage of time for object u Message is labeled on arrows to show messages sent to or received by actor or system Systems Analysis and Design in a Changing World, 4 th Edition 32

7 SSD Lifelines u Vertical l u If line under object or actor Shows passage of time vertical line dashed l Creation and destruction of thing is not important for scenario u Long l narrow rectangles Activation lifelines emphasize that object is active only during part of scenario Systems Analysis and Design in a Changing World, 4 th Edition 33

7 SSD Messages u Internal events identified by the flow of objects in a scenario u Requests from one actor or object to another to do some action u Invoke a particular method Systems Analysis and Design in a Changing World, 4 th Edition 34

7 Repeating Message (Figure 7 -15) Systems Analysis and Design in a Changing World, 4 th Edition 35

7 Developing a System Sequence Diagram u Begin with detailed description of use case from fully developed form or activity diagram u Identify input messages u Describe message from external actor to system using message notation u Identify and add any special conditions on input message, including iteration and true/false conditions u Identify and add output return messages Systems Analysis and Design in a Changing World, 4 th Edition 36

Activity Diagram and Resulting SSD for Telephone Order Scenario (Figures 7 -16 and 7 -17) Systems Analysis and Design in a Changing World, 4 th Edition 7 37

7 SSD of the Web Order Scenario for the Create New Order Use Case (Figure 7 -18) Systems Analysis and Design in a Changing World, 4 th Edition 38

7 Integrating Object-Oriented Models u Complete use case diagram is needed to understand total scope of new system u Domain model class diagrams should also be as complete as possible for entire system u With iterative approach, only construct use case descriptions, activity diagrams, and system sequence diagrams for use cases in iteration u Development of a new diagram often helps refine and correct previous diagrams Systems Analysis and Design in a Changing World, 4 th Edition 39