[use cases] Why pre-conditions/post-conditions?

Hi all,

Jean-Yves asked a question during the last Use Cases TF telecon that we
were not able to get to during the call. The gist of his question was this:

What's the purpose of the pre-conditions and post-conditions sections in
each use case?

To see an example of this type of section, look here:

https://dvcs.w3.org/hg/webpayments/raw-file/default/latest/use-cases/index.html#h4_pre-conditions

David Ezell suggested that we change the "Requirements" section to this.
I think it has helped clarify expectations related to each use case. A
very brief definition:

A use case's pre-conditions indicate what the system will ensure is true
before letting the use case start.

A use case's post-conditions indicate what will be true after the use
case finishes.

There is a good, but lengthy, introduction to
pre-conditions/post-conditions here:

http://www.batimes.com/articles/use-case-preconditions-a-best-kept-secret.html

The reason that pre-conditions and post-conditions are important is
because they help us understand how all these use cases fit together (or
if we're missing a use case). They also spell out what we expect the use
case to do w/o having to prescribe requirements.

-- manu

-- 
Manu Sporny (skype: msporny, twitter: manusporny, G+: +Manu Sporny)
Founder/CEO - Digital Bazaar, Inc.
blog: The Marathonic Dawn of Web Payments
http://manu.sporny.org/2014/dawn-of-web-payments/

Received on Monday, 23 February 2015 15:14:32 UTC