The Navigation and Policy Layer

The spatial metaphor continues to serve us well in describing the conceptual model of interactive systems. We use the term “navigation” to describe users getting from one place to another. We use the term “navigation map” to represent the route instructions, as it were, throughout the conceptual model. Here are some details about navigation and navigation maps.

The Conceptual Navigation Map: Moving Between Conceptual Model Elements

The conceptual navigation map shows “routes” the user can or is required to take through the configuration to perform and conclude all required steps for accomplishing a goal. Showing “routes” in the navigation map includes the following:

1. The entry and exit points for starting and concluding the interaction.

2. The direction of each link between conceptual elements in the configuration; some links are one-way and some are two-way.

Figure 6.1 shows one conceptual model configuration (configuration C from Figure 5.1) with three different navigation maps.

In conceptual navigation map C1, navigation starts and ends with conceptual model element 1. From that element, one can proceed to conceptual model element 2 or 4. When one concludes the interaction at conceptual model element 2 or 4, one navigates back to conceptual model element 1 in order to exit. Finally, one can continue from conceptual model element 2 to conceptual model element 3, and once one concludes the interaction in conceptual model element 3, one has to navigate back to conceptual model element 2. Conceptual navigation map C2 is identical to C1 with the exception that one can conclude the interaction in conceptual model element 4 and exit from there without having to go back to conceptual model element 1. Finally, in conceptual navigation map C3, one can also conclude the interaction in conceptual model elements 2 and 3 and exit from each of them without having to retrace the navigation backward in order to exit.

The following two primary considerations influence the route a user takes between linked conceptual model elements to perform all the tasks required to accomplish a goal:

1. The conceptual model configuration

2. Decisions on the workflow and dynamics of the interaction

Each of the links in a conceptual model configuration is a possible route the user can take. However, having a link between elements does not always tell us if it is a one-way or a two-way route. In addition, it does not tell us where the entry and exit points are. The decision on those latter parameters is influenced by workflow.

However, the physical location of each conceptual element also influences the route characteristics. For example, look at elements 2 and 3 in any of the three examples in Figure 6.1. The map indicates that there is a two-way route between these two elements. Will the navigation be the same if each of the two elements is in a separate window as compared to a case where both elements are in the same window but are in two separate tabs? This brings us to the next important aspect of the conceptual model: physical places. In particular, we will discuss how the physical place of conceptual elements can affect navigation and interaction.

Physical Places for the Conceptual Elements

So far, we used the spatial term “places” to talk about conceptual elements. It is very important to emphasize that this is in a strict metaphorical sense and not in the physical sense of places. However, the correspondence between the metaphorical “places” and their physical location is significant when we determine that physical location, the “distances” between “places,” and the navigation among them.

Conceptual model elements could sometimes have a correspondence of one-to-one with their physical location. For example, a “place” could be a window. Yet, at other times, there would not be such correspondence. For example, Figure 6.2 illustrates a configuration of three conceptual elements representing three metaphorical “places” with “place” 1 linked to “places” 2 and 3. These metaphorical “places” can be located physically in various ways.

The three elements could be in three distinct physical places (e.g., three windows as in A in Figure 6.2). Such a model would reflect link strength that is similar between element 1 and elements 2 and 3, respectively. It could also reflect two similar (same frequency or same importance) interaction flows, from element 1 to element 2 or from element 1 to element 3.

Alternatively, “places” 2 and 3 can be located within a single physical place hosting also conceptual element 1 (see B in Figure 6.2). Such a configuration would represent tighter relations between element 1 as a parent to elements 2 and 3. It could also reflect an interaction flow between elements 2 and 3 that must remain within the context of the parent element 1.

Figure 6.3 illustrates another scheme for assigning conceptual elements to physical places. Element 1 is linked to elements 2 and 4 in the conceptual model. In addition, element 3 is linked with element 4. One possible physical assignment for this model is shown in A; “places” 2 and 3 can physically appear within a single physical place hosting also conceptual element 1, whereas “place” 4 appears as a pop-up window. This assignment reflects the tighter link between elements 2 and 3 and their “distance” from element 4. Alternatively, a possible hierarchical link between elements 2 and 3 can be physically assigned such that elements 2 and 3 appear as “places” within the window hosting also conceptual element 1, with element 3 being an expansion of element 2. Element 4 is assigned to a separate pop-up window.

Determining the assignment of the conceptual elements to physical places has significant implications on the navigation map and navigation policy. As is discussed soon in this part of the book, it also has implications to human performance, usability, and user experience.

Navigation Policy: The “Rules of the Road”

Effective map and route instructions must include the rules that govern the navigation. Can we go anywhere we want at any time we want? Similarly, the conceptual navigation map must include those rules, which we refer to as the navigation policy.

Design decisions regarding the conceptual navigation map go hand in hand with decisions regarding the physical places and the policy of the navigation. These decisions must consider a fundamental question: Should the user be able to perform more than one task at a time? In terms of interaction flow, the implications of this question are the following: Is the user required to fully or partially complete a task before moving on to the next task, and is the user required to complete a given task, move on to another task and complete it, and then return to complete the original task?

In terms of the conceptual model, the policy deals fundamentally with the challenge of modality: While interacting with a given conceptual element in a given physical place, can the user also interact with another conceptual element, in the same physical place or different places? When the answer to this question is yes, we refer to it as a modeless policy. A modeless conceptual model element allows interactions with other conceptual model elements at the same time. When the policy confines the user to interacting with only one conceptual element in a single physical place at a time, we refer to it is a modal policy. A modal conceptual model element is one that does not allow interaction with any other conceptual model element at the same time.

The conceptual navigation map in Figure 6.4 is an example of the relations between the navigation policy and the physical places of the conceptual elements. The navigation policy shown in part A...