Chapter 4 – Conceptual Design: System Purpose, Actors, Features and UML Use Cases
CHAPTER OBJECTIVES (YOU SHOULD BE ABLE TO):
1. Define and give examples of the purpose of an information system.
2. Describe and give examples of actors.
3. Describe and give examples of features in an information system.
4. Define the UML Use Case notation and be able to draw a use case diagram.
Gettingstarted! For many people, these two words represent an enormous hurdle or mountain to climb over. That term paper! That big test to study for! The whole apartment needs cleaning! Writing all those "thank you" letters! Many projects seem overwhelming as we think about just getting started.
Getting started with the technical/engineering aspects an information systems development project can alsobe difficult because there are so many ways in which one could actually begin a project—for this discussion we are omitting the project management aspects associated with starting and keeping track of an information systems project status. You may recall that a few "ways to get started on an information systems development project" was discussed in Chapter 2 as part of the requirementsdetermination discussion. In that chapter three dominant problem-solving strategies were identified—function, data, and object. To review briefly, the functional problem-solving strategy approaches a problem by first identifying the actions the system must accomplish, such as "register for a course", "drop a course", "check out a movie video", and so on. The data problem-solving strategy approaches a problemby first identifying the data that the system is responsible for, such as "student information", "course information", "schedule information", "movie video information", and so on. Finally, the object problem-solving strategy approaches a problem by simultaneously focusing on objects, such as people, places, things and concepts and the object's attributes (data) and operations (services). Forobvious reasons an object-oriented problem-solving strategy best fits with an object-oriented systems analysis and design methodology. Because of this, we will begin by identifying the information systems purpose or mission. Then we will identify the most important features to be performed by the information system that will naturally lead us into the creation of Use Cases that are object-oriented.INFORMATION SYSTEM PURPOSE
The overriding purpose of any information system is to support the mission of the enterprise. For example, Microsoft is ultimately in the software business to provide a good return on investment for its stockholders. To do this Microsoft makes and sells software (along with other services). One could then say that, "The overriding purpose of Microsoft's Windows 2000Operating System software is to contribute to the revenue stream at Microsoft." In another example, Amazon.com is similarly in business to do the same thing—provide a good return on investment for its stockholders. Amazon.com's web-based storefront software's purpose is to facilitate customers purchasing products from Amazon.com thus contributing to its revenue stream.
Every information systemhas a purpose or mission that it is intended to fulfill regardless of whether the information system is, 1) in the form of a shrink-wrapped box of software (and other goodies) for sale, 2) embedded within another type of device or appliance such as a cell phone or pager, or 3) used to support the internal operations of an enterprise such as a web-based product order fulfillment system. As statedat the start of the preceding paragraph, an information system is intended via its purpose to support the overall mission of the enterprise in some way. Sometimes this support is obvious and significant—such as each of the above examples—and other times its support is not obvious and perhaps not terribly significant.
Identifying the purpose of an information system is sometimes easy and almost...
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