Systems Analysis ITEC 3155 Modeling System Requirements Part

Systems Analysis – ITEC 3155 Modeling System Requirements – Part 1 5

5 Learning Objectives u Explain the many reasons for creating information system models u Describe three types of models and list some specific models used for analysis and design u Explain how events can be used to define activities and use cases u Identify and analyze events to which a system responds Systems Analysis and Design in a Changing World, 4 th Edition 2

5 Overview u Models created during analysis phase activity – Define system requirements u Two concepts help identify functional requirements in the traditional approach and object-oriented approach l Events that trigger use cases l Things in the users’ work domain Systems Analysis and Design in a Changing World, 4 th Edition 3

5 Models and Modeling Why Model? u Models assist with communication l Standard notations specific to certain disciplines l Musical notation Systems Analysis and Design in a Changing World, 4 th Edition 4

5 Models and Modeling (cont. ) l Mathematical notation l Electrical schematic Systems Analysis and Design in a Changing World, 4 th Edition 5

5 Models and Modeling (cont. ) Why Model? u Provides a common “language” to bring together project stakeholders involved in systems development u Process of creating models helps analyst clarify and refine design u Document u Part functional requirements of the system documentation Systems Analysis and Design in a Changing World, 4 th Edition 6

5 Models and Modeling (cont. ) u Analyst describes information system requirements using a collection of models u Complex systems require more than one type of model u Models represent some aspect of the system being built Systems Analysis and Design in a Changing World, 4 th Edition 7

5 Reasons for Modeling (Figure 5 -2) Systems Analysis and Design in a Changing World, 4 th Edition 8

5 Types of Models u Different types of models are used in systems development l Business Models – abstract representation of a business that provides a simplified look at various aspects of the business. Systems Analysis and Design in a Changing World, 4 th Edition 9

5 Types of Models u Different types of models are used in systems development l Requirements Models u Mathematical – formulas that describe technical aspects of the system u Descriptive – narrative memos, reports, or lists that describe aspects of the system u Graphical – diagrams and schematic representations of some aspect of the system Systems Analysis and Design in a Changing World, 4 th Edition 10

5 Types of Models Systems Analysis and Design in a Changing World, 4 th Edition 11

5 Some Descriptive Models (Figure 5 -3) Systems Analysis and Design in a Changing World, 4 th Edition 12

Overview of Models Used in Analysis and Design 5 u Analysis phase activity named “define system requirements” l Logical models l Provide detail without regard to specific technology u Design phase l Physical models l Provide technical details l Extend logical models Systems Analysis and Design in a Changing World, 4 th Edition 13

5 Models Created by Analysis Activities (Figure 5 -4) Systems Analysis and Design in a Changing World, 4 th Edition 14

5 Models Used in Design (Figure 5 -5) Systems Analysis and Design in a Changing World, 4 th Edition 15

5 Events, Activities, and Use Cases u u Use Case l An activity the system performs in response to a user request l A “case” where the system is used by actor Techniques for identifying use cases l Identify user goals u u l Each goal at the elementary business process (EBP) level is a use case EBP – a task performed by one user, in one place in response to a business event, that adds measurable business value, and leaves system and data in consistent state Event decomposition technique Systems Analysis and Design in a Changing World, 4 th Edition 16

Identifying Use Cases Based on User Goals (Figure 5 -6) Systems Analysis and Design in a Changing World, 4 th Edition 5 17

5 Event Decomposition u Business events trigger elementary business processes (EBPs) u EBPs are at correct level of analysis for use cases u Identify business events to decompose system into activities/use cases u Event decomposition is, therefore, used by l Traditional approach to identify activities l OO approach to identify use cases Systems Analysis and Design in a Changing World, 4 th Edition 18

5 Types of Events u External l Outside system l Initiated by external agent or actor u Temporal l Occur as result of reaching a point in time l Based on system deadlines u State l (Internal) Something inside system triggers processing need Systems Analysis and Design in a Changing World, 4 th Edition 19

Events Affecting a Charge Account Processing System that Lead to Use Cases (Figure 5 -7) Systems Analysis and Design in a Changing World, 4 th Edition 5 20

5 External Event Checklist (Figure 5 -8) Systems Analysis and Design in a Changing World, 4 th Edition 21

5 Temporal Event Checklist (Figure 5 -9) Systems Analysis and Design in a Changing World, 4 th Edition 22

5 Identifying Events u Can be difficult to determine u Often u May confused with conditions and responses be useful to trace a transaction’s life cycle u Certain events left to design phase l System controls to protect system integrity l Perfect technology assumption Systems Analysis and Design in a Changing World, 4 th Edition 23

Sequence of Actions that Lead Up to Only One Event Affecting the System (Figure 5 -10) Systems Analysis and Design in a Changing World, 4 th Edition 5 24

Sequence of “Transactions” for One Specific Customer Resulting in Many Events (Figure 5 -11) Systems Analysis and Design in a Changing World, 4 th Edition 5 25

Events Deferred Until the Design Phase 5 (Figure 5 -12) Systems Analysis and Design in a Changing World, 4 th Edition 26

5 Events in the RMO case u Important l Customer checks item availability, customer places order, customer changes or cancels order u Other l external events involve departments Shipping fulfills order, marketing sends promotion to customer, merchandising updates catalog u Temporal l external events involve customers events include periodic reports Time to produce order summary reports, Time to produce fulfillment summary reports Systems Analysis and Design in a Changing World, 4 th Edition 27

Information about Each Event in an Event Table: 5 Catalog of Information about Each Use Case (Figure 5 -15) Systems Analysis and Design in a Changing World, 4 th Edition 28

RMO Event Table (Figure 5 -6 partial) Systems Analysis and Design in a Changing World, 4 th Edition 5 29

5 Next Class u Quiz 2 u Chapter l u 5 continued Lab – Event Table Exam 1 is next Monday!!!!!!! Systems Analysis and Design in a Changing World, 4 th Edition 30