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ChaPter 2 • underStanding and modeling organizational SyStemS 31

MaC appeal

Microsoft Visio makes it easy for a systems analyst to draw E-R diagrams as well as most of the
other diagrams found in this book, but it is available only for PCs. Mac users have an alternative,
OmniGraffle Professional. OmniGraffle is easier to use than Microsoft Visio because its drag-and-
drop interface is smoother and more intuitive.
It also features a “smart guide” that uses pop-up distance markers to help position the symbols
in the correct places. Many symbols, like those used in E-R diagrams, are built in, but OmniGraffle
also lets the user search a third-party library called Graffletopia to find UML and other specialized
symbols.

Figure 2.MAC
OmniGraffle from The Omni Group is an easy-to-use and powerful drawing package. (Screenshot
from OmniGraffle, a registered trademark of the Omni Group. Graphic reprinted with permission.)

An analyst develops use cases in a cooperative effort with the business experts who help
define the requirements of the system. A use case model provides an effective means of commu-
nication between the business team and the development team. A use case model partitions the
way the system works into behaviors, services, and responses (the use cases) that are significant
to the users of the system.
From the perspective of an actor (or user), a use case should produce something that is of value.
Therefore, the analyst must determine what is important to the user and remember to include it in
the use case diagram. For example, is entering a password something of value to the user? It may be
included if the user has a concern about security or if it is critical to the success of the project.
Use Case Symbols
A use case diagram contains the actor and use case symbols, along with connecting lines. Actors
are similar to external entities; they exist outside the system. The term actor refers to a particu-
lar role of a user of the system. For example, an actor may be an employee but also may be a