The Presentation Requirement Pattern

Presentation Intent

The intent of the Presentation pattern is to describe data the application must exhibit. Presentation enables authors to require an application to exhibit data without specifying the exact implementation for how the information is specified.

Also Known As

Present, Display

Motivation

One of the primary interface mechanisms utilized by today's applications is through human vision. The steps that comprise this interface are:

1. The application displays some information.
2. The user sees this information.
3. The user acts on this information.

Examples abound of this type of interface. A specific example is an e-mail utility. When I wish to know if I have new mail, I start this application which, in turn, presents a list of my new mail messages.

Unfortunately, this visual interface often sneaks into specification documents, jading and restricting possible implementations. As a result, other possible implementations are overlooked. To remedy this situation, it is sufficient that the document simply requires that the application "Present" a list of data items. For the e-mail system described above, the solution is as follows:

Present New E-mail Messages

Include Unread E-mail Messages

The E-mail Application will include as part of the "Present New E-mail Messages" presentation any e-mail received by the application not yet read using the "Read E-mail" feature.

Include E-mail Subject

The E-mail Application will include as part of "Present New E-mail Messages" presentation the "Subject" data item included as part of the e-mail data item described in the data requirement section.

Applicability

Use Presentation when:

• the application must interface with a human user via one or more human senses; or
• the application must interface with a software or hardware component that will select information from a list of options.

Consequences

Presentation has the following benefits and liabilities:

Focuses on data items. Presentation enables the author to focus on the information that must be displayed and not the method for how that information is exhibited.

Example Implementations

Examples of implementing Presentation include:

• a pager that uses different vibration patterns to indicate the priority of a page
• a dashboard that displays the operational condition of a vehicle
• a projector clock that displays time on the ceiling.