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

On 2015-02-23 Manu wrote:
> David Ezell suggested that we change the "Requirements" section to this.

To be clear, preconditions and postconditions don't replace requirements.  They >do< provide a helpful grounding that is appropriate at this point in the maturity of the use cases.

Preconditions and postconditions are well-known components of use cases[1].  (Alistair Cockburn (among others) has championed this way of working.)

We can/should address requirements when we reach the right level of maturity.

Best regards,
David

[1] http://en.wikipedia.org/wiki/Use_case


-----Original Message-----
From: Manu Sporny [mailto:msporny@digitalbazaar.com]
Sent: Monday, February 23, 2015 10:14 AM
To: Web Payments IG
Subject: [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/


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Received on Monday, 23 February 2015 17:16:28 UTC