Download
1 / 11
110 likes | 462 Views
CIS 321—IS Analysis & Design. Chapter 5: Modeling System Requirements—Events and Things. 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 _________.
E N D
CIS 321—IS Analysis & Design Chapter 5: Modeling System Requirements—Events and Things
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
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
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
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
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
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
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
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
The Entity-Relationship Diagram Customer Cust ID Name Address Phone Order Order ID Date Amount Exactly one customer can place 0 or more orders
The Class Diagram Customer Cust ID Name Address Phone Account Acct Num Balance makeDep makeWithdrawal • 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 1 0…* SavAcct intRate CheckAcct minBalance
