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Chapter 22. Essentially Speaking > Essential Interfaces

Essential Interfaces

User interface design is one promising application of essential models. Essential use case modeling is an approach that extends Jacobson's object-oriented use cases (Jacobson et al. 1992) to apply to user interface design. An essential use case is an abstract scenario for one complete and intrinsically useful interaction with a system as understood from the perspective of the user's intentions or purpose. It is a generalized description of a kind or class of use to which a system may be put, conveying the user actions and system responses [*] in simplified and generalized form. The idea is to design interfaces to fit intentions— what users want to accomplish—with a minimum of presuppositions about technology, such as the shape of visual widgets or even the devices to be used for interaction.

[*] These two sides of the model are probably even better characterized as user intentions and system responsibilities, which is precisely what they are called in usage-centered design, an approach based on essential use cases (Constantine and Lockwood 1999).

For example, consider the task of withdrawing cash from an automatic teller machine. A physical model might take this form: customer inserts card; system reads magnetic stripe, requests PIN; user types PIN; system confirms PIN, offers menu of transactions; user keys in selection; system offers menu of accounts; user keys in selection; system requests amount; user keys in amount and presses confirmation button; system spits out cash; user takes the money and runs. What could be simpler?


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