Of course, there is no simple algorithmic test, but here is how I view it.
An essential use case is "ready" when four things are true.
(1) It is expressed at an approprate level of abstraction. It is abstract
and generalized but still specific to the particular task case and the
application being designed. In other words, it is not "unsuitably vague."
("Expressing needs" as a user intention is unsuitably vague; "specifying
kinds of entertainment is of interest" is not.)
(2) It is technology- and implementation-independent. It has been purged of
all technological or implementation terms and of all references, explicit or
implicit, to specific solutions. This includes hidden assumptions in such
technology-oriented words as "list" (implies a list of items). Seemingly
innocent common words like "search" often carry implied baggage. (A user may
intend to "find" or "get" or "identify" something, but "search" is a
specific technology solution, not a user intention. The moment you use the
word, it becomes all but impossible not to visualize a search box with a
(3) It is expressed in terms of ordinary user language and the defined
vocabulary of the subject matter or application domain. Elements of the
subject matter or application domain are correctly and consistently
(4) It is complete, enabling the user to perform the overall intention it
represents. We verify completeness by walking through the task case, asking
whether the user could complete the task assuming a user interface that
supplied the necessary features and a system that carried out its
With regards to the last criterion, completeness may refer only to the
"happy case" or also to exceptions and alternatives, depending on resources
and level of formality of the process. If it is a small application being
designed under agile conditions, extensions may be allowed to emerge as
needed rather than being elaborated and validated explicitly at the outset.
--Larry Constantine, IDSA [mailto:lconstantine@...
Chief Scientist | Constantine & Lockwood, Ltd. | www.foruse.com
> -----Original Message-----
> From: news [mailto:news@...] On Behalf Of Agustín Villena
> Sent: Thursday, 24 February 2005 1:58 PM
> To: firstname.lastname@example.org
> Subject: [agile-usability] Re: Re: Task model => User Interface ...
Through task (esential use)
> Hi Larry!
> The problem that I faced when trying to apply U-CD (in the Larry way) is
> that Is really dificult to know when the esential use case is "ready".
> Thnking "a la" Test Driven Development: what tests the essential use case
> should pass to be considered "ok"?