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Author Archives: Glennan Carnie
The Baker’s Dozen of Use Cases
Rule 9 – Build yourself a Data Dictionary
Transactions between the actors and the system typically involve the transfer of data. This data has to be defined somewhere. If you’ve built a Domain Model ( see Part 5 – here) most of the data will be identified there; but even then the class diagram is not always the most practical place to capture the sort of information you need to record.
Another way to capture this information […]
Posted in Design Issues
Tagged Analysis, Baker's Dozen, Data Dictionary, Requirements, UML, Use Case
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The Baker’s Dozen of Use Cases
RULE 8: Don’t describe the user interface
For many users the user interface is the system. Prototypes and mock-ups of the man-machine interface (MMI) are a fantastic way of eliciting requirements and use case behaviours from your stakeholders. And when defining use case descriptions adding MMI ‘screenshots’ and images can help illuminate the behaviour of the system to your customers.
It is very tempting to describe use case transactions in terms of MMI elements, in an attempt to make them more understandable […]
Posted in Design Issues, General
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The Baker’s Dozen of Use Cases
RULE 7: Describe ALL the transactions
A use case, as the name implies, describes the usage of the system from the point of view of some beneficiary (our Actor). It is NOT (as I seem to spend my whole life telling people) is just the system function, organised as some sort of graphical ‘sub-routine’. This means the use case description must include the expected behaviour of the actors as well as the expected behaviour of the system.
This can […]
Posted in Design Issues
Tagged Analysis, Baker's Dozen, Requirements, Transaction, UML, Use Cases
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The Baker’s Dozen of Use Cases
RULE 6: If it’s not on the Context or Domain models, you can’t talk about it
(If you haven’t already read it, I’d suggest having a quick look over Part 1 of the Baker’s Dozen to familiarise yourself with the fundamentals of use case descriptions.)
Engineers love to solve problems. It’s what they do. A use case model though is not a design model – it’s an analysis model. Use cases describe what the system should do, and in […]
The Baker’s Dozen of Use Cases
RULE 5: Focus on goals, not behaviour
There is a subtle distinction between the functional behaviour of the system and the goals of the actors. This can cause confusion: after all, the functional behaviour of the system must surely be the goal of the actor?
It is very common, then, for engineers to write use cases that define, and then describe, all the functions of the system. It is very tempting to simply re-organise the software requirements into functional areas, each […]
Posted in Design Issues, UML
Tagged Analysis, Baker's Dozen, Design Case, Goals, Requirements, Use Case
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The Baker’s Dozen of Use Cases
RULE 4 : The “Famous Five” of requirements modelling
As I discussed in Rule 1, a common misunderstanding of use cases is that they are the software requirements. Unfortunately, this isn’t the situation. Use cases are merely an analysis tool – albeit a very powerful tool (when used in the right situation).
Use cases are just one technique for understanding and analysing the requirements. In order to fully understand the requirements our use cases are going to need some […]
Posted in Design Issues, General, UML
Tagged Behaviour, Context, Context Model, Domain, Domain model, Modes model, State Machine, SysML, UML, Use Case
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The Baker’s Dozen of Use Cases
RULE 3: Never mix your Actors
The UML definition of an Actor is an external entity that interacts with the system under development. In other words: it’s a stakeholder.
Having analysed all your stakeholders (see Part 3 ) it’s tempting to stick them (no pun intended) as actors on a use case diagram and start defining use cases for each.
Each set of stakeholders (Users, Beneficiaries or Constrainers) has its own set of concerns, language and concepts:
Concerns.
Each stakeholder group has a different […]
Posted in Design Issues, UML
Tagged Analysis, Baker's Dozen, Requirements, UML, Use Cases
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The Baker’s Dozen of Use Cases
RULE 2: Understand your stakeholders
A Stakeholder is a person, or group of people, with a vested interest in your system. Vested means they want something out of it – a return on their investment. That may be money; it may be an easier life.
One of the keys to requirements analysis is understanding your stakeholders – who they are, what they are responsible for, why they want to use your system and how it will benefit them.
It’s important to […]
Posted in Design Issues, UML
Tagged Analysis, Baker's Dozen, Requirements, Stakeholder, UML, Use Cases
1 Comment
The Baker’s Dozen Of Use Cases
RULE 1: Use Cases Aren’t Silver Bullets
There are a couple of popular misconceptions around use cases:
Misconception 1: The use cases are the requirements of the system
Contrary to what many engineers believe (and many authors have written) the complete set of use cases do NOT constitute its full set of requirements for the system.
A use case model is an analysis tool. They are a mechanism for organising the functional behaviour of the system and reflecting it back to the […]
A Brief Introduction to Use Cases
Since Jacobson defined use cases back in 1992 they have been subject to a vast range of interpretations. Alistair Cockburn, author of Writing Effective Use Cases states:
“I have personally encountered over 18 different definitions of use case, given by different, each expert, teachers and consultants”
I am no different: this is my personal interpretation of use case modelling and analysis. To qualify this statement though, this methodology is based on nearly a decade of requirements definition work on a number high integrity projects, […]