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We are going to use a layered framework to define and analyze the conceptual model. Why layered? Think of the layered onion metaphor. The idea behind this popular metaphor is that we peel off one layer after another to reach the core and discover the real taste of the onion. When it comes to user interfaces of interactive systems, we can take what we see in the UI as the outer layer and imagine there are inner and hidden layers that we need to peel off to uncover the core.


In the first part of the book where we introduce and analyze conceptual models, we peel off layers to uncover the core, the underlying conceptual model. In the second part of the book where we methodically construct a conceptual model, we go the other way: we add one layer on top of another, from the abstract to the most concrete. Figure 3.1 shows the layered framework representing the entire context in which the conceptual model resides.


The framework, from the bottom up, consists of five layers:


1. The function level consists of functional chunks - groups of tasks and objects and their associated parameters that the user uses to accomplish goals.


2. The configuration level consists of the conceptual model elements - the metaphorical "places" the user must visit to perform each set of functions and the links between the "places."


3. The navigation and policy level depicts the navigation and navigation rules - the "routes" the user takes between "places," the physical elements containing one or more conceptual "places," and the policy governing the interrelations among the physical elements.


4. The form level consists of detailed conceptual elements serving as the transition from conceptual to detailed design.


5. The details level consists of user interface elements - detailed look and feel of each UI element at each place the user visits to perform tasks.


The conceptual design deals with what the user does and where, but without the details. In terms of this framework, conceptual design spans the function, configuration, and navigation and policy levels. The transition to the detailed design takes place on the form level, introducing details and finally transforming the conceptual design into a full and detailed user interface.


FIGURE 3.1: The layered framework representing the conceptual model and detailed design.

Details - User Interface Elements
Form - Detailed Conceptual Elements
Navigation and Policy - Physical Model Elements
Configuration - Conceptual Model Elements
Function - Functional Chunks - Date & Time Recurrence range Other parameters - Start time End time Time zone


Throughout the analysis and discussion of the conceptual model, we will be peeling the onion layers. In other words, we will reverse engineer the calendar examples from the previous chapter to uncover the elements and characteristics of their respective underlying conceptual models.