CIS 321—IS Analysis & Design Chapter 5: Modeling System Requirements—Events and Things

2 The Purpose of Models Analysis models are created in the sub-phase, _______ system requirements. A model is an abstraction of reality. An abstraction is a representation of the _________. The modeling process is as valuable as the product. Reasons for modeling: discovery of new requirements understanding through simplification _______________ with users and developers

3 Types of Models Mathematical a cost-benefit analysis in a spreadsheet a formula for network response time Descriptive memos, reports, lists ____________ Graphical screen or report layout designs abstract models using standard symbols the _____ is a standard modeling notation for OOSD

4 Events and System Requirements Event something important that happens at a place and time An event is something that may need to be recorded An event triggers a process and is often accompanied by ______ A system event is “something important that happens at a place and time” and “may need to be recorded” in the system Analysis deals with events related to functional requirements, not __________ requirements

5 Types of Events External event initiated by an external agent or actor Temporal event initiated by _______ may be periodic State event initiated by a change in an entity’s state

6 Event Table The name of the event and its characteristics can be organized in an event table Characteristics of an event trigger: signal that immediately follows the event to begin an activity/use case _______: the entity that caused the event (agent or time) activity/use case: the process initiated by the event response: output resulting from the activity/use case ____________: agent or actor that receives the response

7 Things and System Requirements Thing a unique important part of the system’s problem domain for which information should be stored Procedure for identifying system “things” using the event table, identify all of the _______ using other existing models, add more nouns refine the list of things to the essential

8 Relationships Among Things Relationship an important association between two things in the system e.g., customer places order, Shipping Dept. ships order Cardinality (or multiplicity for OO) the quantity of things associated on each end of a relationship at a point in time one customer can place zero to many orders Binary relationship—between two different things Unary relationship—a thing with itself (__________) n-ary relationship—n > 2

9 Things and Their Attributes Attribute a single piece of information about a thing (e.g., SSN) Compound attribute a collection of related attributes (e.g., name, address) In traditional systems development a thing is called a “data entity” that has relationships entities are modeled using an entity-relationship diagram (ERD) In OO systems development a thing is called an “______” with attributes and behaviors classes of objects are modeled using a class diagram

10 The Entity-Relationship Diagram Customer Cust ID Name Address Phone Order Order ID Date Amount Exactly one customer can place 0 or more orders

11 The Class Diagram Generalization relationship “is a” or inheritance superclass and subclass Association relationship “has a” or whole-part aggregation—part can exist independently composition—part cannot exist independent of the whole Customer Cust ID Name Address Phone Account Acct Num Balance makeDep makeWithdrawal SavAcct intRate CheckAcct minBalance 1 0…*