Meaning of "Design for the unanticipated user"

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

I am starting to get an understanding of the phrase "design for the unanticipated user." Below I have extended the example that I presented earlier and have attempted to identify the key features of "designing for the unanticipated user." 

I am eager to hear your thoughts on this. Have I captured all that's involved in "designing for the unanticipated user?"   /Roger


CURRENCY EXCHANGE RATE WEB SERVICE

Suppose you deploy a web service to provide currency exchange rates to banks, for use in calculating monetary exchanges. A user (bank) sends two currencies, e.g. 

    USD and CAD 

and your web service responds with today's exchange rates, e.g. 

    Saturday, Jan. 17, 2009: 1 USD = 0.807473 CAD, 1 CAD = 1.23842 USD


THE UNANTICIPATED USER

The "unanticipated user" means the users of your web service may be unknown to you. It does not mean that requests made by users are unknown or arbitrary. For example, your web service can't be expected to handle requests from users wanting to know the temperature of Nome, Alaska! Your service only handles requests for currency exchange rates; however, the users issuing the requests may be unknown.


NEW TYPES OF USERS

Shortly after deploying the web service its logs reveal that not only are banks using your web service but also individuals planning holiday trips abroad are using it!


DIFFERENT INFORMATION DEEMED IMPORTANT

You also discover that some users are using your web service not for the exchange rate information but for getting today's date!


EXPANDING USAGE

The types of users has expanded from banks to lone individuals.

The ways the information is used has expanded from monetary transactions to holiday planning.

The information deemed important has expanded: some (most) users use the web service to get currency exchange rates but a few users use it to get today's date.


KEY FEATURES OF "DESIGN FOR THE UNANTICIPATED USER"

"Design for the unanticipated user" means you recognize that:

   - the types of users will change

   - the ways the information is used will change

   - the parts of the information that are deemed important
     and relevant by users will change

Consequently, you need to monitor your web service and note changes in usage. This information will give you the knowledge of how to evolve your service to better accommodate your users.