1. 5 Chapter 5: Modeling Systems Requirements: Events and Things Systems Analysis and Design in a Changing World

2. 5 Systems Analysis and Design in a Changing World, 3rd Edition 2 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 system requirements u Identify and analyze events to which a system responds u Recognize that events trigger system activities or use cases

3. 5 Systems Analysis and Design in a Changing World, 3rd Edition 3 Learning Objectives ( continued ) u Explain how the concept of things in the system also defines requirements u Explain the similarities and the differences between data entities and objects u Identify and analyze data entities and objects needed in the system u Read, interpret, and create an entity-relationship diagram u Read, interpret, and create a class diagram

4. 5 Systems Analysis and Design in a Changing World, 3rd Edition 4 Overview u Document functional requirements by creating models u Models created during analysis phase activity: Define system requirements u Two concepts define system requirements in traditional approach and object-oriented approach l Events l Things

5. 5 Systems Analysis and Design in a Changing World, 3rd Edition 5 Models and Modeling 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 u Process of creating model helps analyst clarify and refine design u Models assist communication with system users

6. 5 Systems Analysis and Design in a Changing World, 3rd Edition 6 Reasons for Modeling

7. 5 Systems Analysis and Design in a Changing World, 3rd Edition 7 Types of Models u Different types of models are used in information systems development l Mathematical - formulas that describe technical aspects of the system l Descriptive - narrative memos, reports, or lists that describe aspects of the system l Graphical - diagrams and schematic representations of some aspect of the system

8. 5 Systems Analysis and Design in a Changing World, 3rd Edition 8 Overview of Models Used in Analysis and Design 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

9. 5 Systems Analysis and Design in a Changing World, 3rd Edition 9 Models Used in Analysis

10. 5 Systems Analysis and Design in a Changing World, 3rd Edition 10 Models Used in Design

11. 5 Systems Analysis and Design in a Changing World, 3rd Edition 11 Events and System Requirements u Events l Occurrences at a specific time and place l Trigger all system processing u Requirement definition l Determine relevant events u External events first u Temporal events second l Decompose system into manageable units

12. 5 Systems Analysis and Design in a Changing World, 3rd Edition 12 Events Affecting a Charge Account Processing System

13. 5 Systems Analysis and Design in a Changing World, 3rd Edition 13 Types of Events u External l Outside system l Initiated by external agent or actor u Temporal l Occurs as result of reaching a point in time l Based on system deadlines u State l Something inside system triggers processing need

14. 5 Systems Analysis and Design in a Changing World, 3rd Edition 14 External Event Checklist

15. 5 Systems Analysis and Design in a Changing World, 3rd Edition 15 Temporal Event Checklist

16. 5 Systems Analysis and Design in a Changing World, 3rd Edition 16 Identifying Events u Can be difficult to determine u Often confused with conditions and responses u May be useful to trace a transaction’s life cycle u Certain events left to design phase l Systems controls to protect system integrity l Perfect technology assumption defers events

17. 5 Systems Analysis and Design in a Changing World, 3rd Edition 17 Sequence of Actions that Lead up to Only One Event Affecting the System

18. 5 Systems Analysis and Design in a Changing World, 3rd Edition 18 Sequence of “Transactions” for One Specific Customer Resulting in Many Events

19. 5 Systems Analysis and Design in a Changing World, 3rd Edition 19 Events Deferred Until the Design Phase

20. 5 Systems Analysis and Design in a Changing World, 3rd Edition 20 Events in the RMO case u Important external events involve customers l Customer checks item availability, customer places order, customer changes or cancels order u Other external events involve departments l Shipping fulfills order, marketing sends promotion to customer, merchandising updates catalog u Temporal events include periodic reports l Time to produce order summary reports, Time to produce fulfillment summary reports

21. 5 Systems Analysis and Design in a Changing World, 3rd Edition 21 Information about each Event in an Event Table

22. 5 Systems Analysis and Design in a Changing World, 3rd Edition 22 RMO Event Table (Figure 5-6 partial)

23. 5 Systems Analysis and Design in a Changing World, 3rd Edition 23 Things and System Requirements u Define system requirements by understanding system information that needs to be stored u Store information about things in the problem domain that people deal with when they do their work u Analysts identify these types of things by considering each event in the event list l What things does the system need to know about and store information about?

24. 5 Systems Analysis and Design in a Changing World, 3rd Edition 24 Types of Things

25. 5 Systems Analysis and Design in a Changing World, 3rd Edition 25 Characteristics of Things u Relationship l Naturally occurring association among specific things l Occur in two directions l Number of associations is cardinality or multiplicity u Binary, unary, ternary, n-ary u Attribute l One specific piece of information about a thing

26. 5 Systems Analysis and Design in a Changing World, 3rd Edition 26 Relationships Naturally Occur Between Things

27. 5 Systems Analysis and Design in a Changing World, 3rd Edition 27 Cardinality/Multiplicity of Relationships

28. 5 Systems Analysis and Design in a Changing World, 3rd Edition 28 Attributes and Values

29. 5 Systems Analysis and Design in a Changing World, 3rd Edition 29 Data Entities u Things system needs to store data about in traditional IS approach u Modeled with entity-relationship diagram (ERD) u Requirements model used to create the database design model for relational database

30. 5 Systems Analysis and Design in a Changing World, 3rd Edition 30 Objects u Objects do the work in system and store information in object-oriented approach u Objects have behaviors and attributes l Class: Type of thing l Object: Each specific thing l Methods: Behaviors of objects of the class u Objects contain values for attributes and methods for operating on those attributes u An object is encapsulated – a self-contained unit

31. 5 Systems Analysis and Design in a Changing World, 3rd Edition 31 Data Entities Compared with Objects

32. 5 Systems Analysis and Design in a Changing World, 3rd Edition 32 Simple Entity-relationship Diagram

33. 5 Systems Analysis and Design in a Changing World, 3rd Edition 33 Cardinality Symbols of Relationships

34. 5 Systems Analysis and Design in a Changing World, 3rd Edition 34 Expanded ERD with Attributes Shown

35. 5 Systems Analysis and Design in a Changing World, 3rd Edition 35 Customers, Orders, and Order Items

36. 5 Systems Analysis and Design in a Changing World, 3rd Edition 36 University course enrollment ERD

37. 5 Systems Analysis and Design in a Changing World, 3rd Edition 37 Refined University course enrollment ERD

38. 5 Systems Analysis and Design in a Changing World, 3rd Edition 38 RMO Customer Support ERD

39. 5 Systems Analysis and Design in a Changing World, 3rd Edition 39 Procedure for Developing an Initial List of Things u Step 1: Using the event table and information about each event, identify all nouns about system u Step 2: Using other information from existing systems, current procedures, and current reports or forms, add items or categories of information needed u Step 3: Refine list and record assumptions or issues to explore

40. 5 Systems Analysis and Design in a Changing World, 3rd Edition 40 The Class Diagram u Models classes of objects instead of data entities u Generalization/specialization hierarchies l General superclasses to specialized subclasses l Inheritance allows subclasses to share characteristics of their superclasses u Aggregation (whole-part hierarchies) l Relates objects and its parts l Defines object in terms of its parts

41. 5 Systems Analysis and Design in a Changing World, 3rd Edition 41 A Generalization/Specialization Hierarchy for Motor Vehicles

42. 5 Systems Analysis and Design in a Changing World, 3rd Edition 42 A Generalization/Specialization Hierarchy for Orders

43. 5 Systems Analysis and Design in a Changing World, 3rd Edition 43 Aggregation or Whole-Part Relationships

44. 5 Systems Analysis and Design in a Changing World, 3rd Edition 44 The Class Symbol for the Class Diagram

45. 5 Systems Analysis and Design in a Changing World, 3rd Edition 45 Bank Account System Class Diagram

46. 5 Systems Analysis and Design in a Changing World, 3rd Edition 46 Enrollment Class Diagram with Association Class

47. 5 Systems Analysis and Design in a Changing World, 3rd Edition 47 RMO Class Diagram

48. 5 Systems Analysis and Design in a Changing World, 3rd Edition 48 Where You Are Headed

49. 5 Systems Analysis and Design in a Changing World, 3rd Edition 49 Summary u Analysis Phase: Define system requirements u Models created to: further learning process, reduce complexity, communicate with team members, and document requirements u Many types of models used: l Mathematical, descriptive, graphical u Key early step in modeling to identify and list: l Events that require a response from system l Things users deal with in work environment

50. 5 Systems Analysis and Design in a Changing World, 3rd Edition 50 Summary ( continued ) u Events are memorable, can be described, and occur at specific time and place u External events occur outside system, triggered by someone interacting with system u Temporal events occur at defined point in time, such as end of day or end of month u State events based on internal system change u Event table records event, trigger, source, activity or use case, response, and destination

51. 5 Systems Analysis and Design in a Changing World, 3rd Edition 51 Summary ( continued ) u Things are what user deals with and system remembers, such as customer placing an order u Traditional approach uses entity-relationship diagrams (ERD) for data entities, attributes of data entities, and relationships between entities l Things are shown as data entities u Object-oriented approach uses class diagrams for classes, attributes, methods of class, and associations among classes l Things are shown as objects belonging to a class