Asur++: a Design Notation for Mobile Mixed Systems

Considering the concept of localisation, the system has to deal with two inputs: the one related to the user's location and the one related to the exhibit's location. Matching these two sources of information may be a problem for the computer system and is similar to a discontinuity problem on the user's side. Solutions to address this problem can be driven by the solutions envisioned when a discontinuity problem is identified on the user's side. It would thus be better to:

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  Use only one reference scheme in which to encode the location information provided by the adapters (similar to a cognitive discontinuity problem)
  
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  Track only one entity (similar to a perceptual discontinuity problem)
  

In this present case, grouping the two adapters may be achieved by using one of the following mechanisms:

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  Avoiding the need of the relationship between the exhibit and the input adapter, or of the relationship between the user and the input adapter.
  
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  Grouping the exhibit with the user or the exhibit with the input adapter;
  

Let us first consider the localisation of the exhibit. A solution could be to use a static model of the positions of the exhibits. In fact this is achievable by adding a field in the exhibit database holding the location of the exhibit in the museum. Consequently, having the position of the visitor in the museum is sufficient to find in the database the exhibit which has the nearest coordinates and thus to display the right information. To represent the existence of a virtual model of the physical exhibit, we refine the ASUR++ component S (computer System) by adding a decoration to the S node: V- R_object (virtual model of the real entity associated with the component R_object). The new ASUR++ diagram is presented on the left-hand side of figure 5.

Fig. 5. Complete ASUR++ description of the scenario using one output adapter and one input adapter when avoiding the localisation need of the exhibit (left) or of the visitor (right).

The role of the grouping mechanism is to physically link a component with an input adapter, so that when this adapter sends information to the system about another component, the system also knows where the information comes from.

One way of implementing this mechanism consists of installing near an exhibit the input adapter responsible for the visitor’s localisation. This is represented by a physical collocation relationship between the exhibit and the input adapter (R_object=A_in). The set of components that make up the exhibit and the input adapter remain static. The system can determine the visitor’s position by associating the visitor’s identity with the exhibit to which the input adapter is collocated. Thus the system can display the right information to the user. To be localised, the visitor, or more exactly the set of component that includes the visitor, has to come near the exhibit. In terms of ASUR++, when the visitor comes near the exhibit, it triggers the transfer of information from the visitor to the input adapter. The following relations emerge: UA_in and U→A_in. The ASUR++ diagram of this system is shown in the left part of figure 6. Examples of devices that might play the role of the component A_in as described here are motion detectors or an rfid tag and sensor. In the later case, the relation denoting the transfer of information between the user and the input adapter requires the addition of the rfid emitter to the set of components carried by the visitor. The relation between the "visitor set" and the "adapter set" is U→A_in. The designer has to think about which component of the "visitor set" to embed: the visitor or the output adapter.

Another way of applying this mechanism is to group the input adapter with the visitor. The information provided to the system by the adapter refers here to the localisation of an exhibit, given that the relationship between the adapter and the visitor is known and fixed. In this case, the input adapter has to be physically collocated with the user (A_in=U) and is added into the mobile "visitor's set". When the visitor approaches the exhibit, it triggers the exchange of information between the exhibit and the input adapter responsible for the localisation of the exhibit: U R_object and its associated triggered relation R_object→A_in. The right side of figure 6 illustrates this alternative. A candidate A_in component for this version would be an rfid on the exhibit or, more elaborately, a camera with an image processing module added in the computer system to automatically recognise the exhibit in front of the camera.