The Commonly Used ATM Use Case Example
Teaches Wrong Concepts
An ATM Is Not a Single System
The proverbial ATM use case example that many use as a simple introduction to use cases is not so simple. It is not a single system. It is documented inaccurately. As a result, beginners learn wrong concepts. Is it surprising that many people find use cases confusing when their introduction to use cases is not clear?
An ATM Is a System of Systems
An ATM itself is actually a system of systems that includes these internal systems, among others, that must work together:
• A screen, usually a touch screen
• A keyboard
• A cash dispenser
• A receipt printer
• A deposit slot
Additionally, an ATM depends on or communicates with at least these other outside systems:
• The electric grid
• A communication system that uses protocols and other standards
• The bank system that issued the card
• A language system, e.g., “Press 1 for English, press 2 for Spanish.”
• Banking regulatory systems Don't we have to document all these systems to produce complete unambiguous requirements?
It Is Better to Teach How to Work with Complexity Upfront
It is not surprising that people are confused by use cases when the most common use case example they learn from ignores complexity. System boundaries are found nowhere. Use cases from completely different systems are documented on the same diagram.We believe that it is better to teach how to work with the complexity that exists. The Building Requirements Consensus™ Methodology is an internally consistent approach that addresses complexity by applying a few principles. Dee Hock, developer of the concept for a global system for the electronic exchange of value that became VISA, says:
"Simple, clear purpose and principles give rise to
complex and intelligent behavior.
Complex rules and regulations give rise to
simple and stupid behavior."
Three Fundamental Concepts
The Building Requirements Consensus™ Methodology is built with the idea of clear principles in mind. There are three fundamental concepts described in Use Case Basics (left navigation button) or directly with these links:
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use case
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system
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role - yes, role and not actor
Like most principles they are easy to say. For example, Einstein’s E=mc2 is easy to say.
Applying the Three Fundamental Concepts
Effectively applying these three simply stated fundamental concepts requires a certain degree of training and experience. Fortunately, it is nowhere near what is required to apply E=mc2!Once you learn the principles of the
Building Requirements Consensus™ Methodology
, you will be surprised by the varied ways you can effectively apply them. You will also be surprised by how many situations that are challenging today become clear tomorrow.
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