2) To use the applet, you will need an appropriate version of Java installed. If you don't see the progress bar of Java indicating that the applet is being loaded, you should check the configuration of your browser.
3) By clicking on the applet, you will be able to use any key to advance the simulation one step. First, you will only see a user with a mobile device. Press any key and two objects will appear (one gray and one blue, which represent the reference objects of a certain query). Press a key again and you will see a set of white circles that represent target objects (i.e., objects that are interesting for the query because they are instances of the relevant classes). Pressing another key, you will see two circles around the reference objects (the extended areas). We want to obtain the set of white circles which are within those areas, and the current locations of such objects, and keep the answer up-to-date. Press another key and you will see why this is so difficult. We have a distributed set of proxies in charge of different geographic areas; therefore, if we want to know the location of a certain object, we need to ask its current proxy. The set of proxies which are relevant to the query will move as the reference objects and their extended areas move. Notice that this distribution is needed for the system to be scalable. Now, as you continue pressing keys, you will se how the network of agents is deployed. Pay attention at the bottom right corner, where you will find the meaning of the different elements shown in the scenario. The messages on the upper right corner are also interesting: they will tell you what is currently happening.
4) Every time a certain agent appears on the screen, you can see the effect of moving certain objects in the scenario (drag and drop any object with the mouse). For example, once the MonitorTracker has appeared, try to move the user under the coverage of a different proxy. Or once a Tracker agent has appeared, try to move its reference object similarly. You are advised to put the object back into its original location (as, for simplicity, it will consider a predefined trajectory and will come back there later anyway).
5) Once the network of agents has been fully deployed, the white circles are numbered. Press any key and they will start moving. On the bottom left corner you will see the objects which are within each of the extended areas in the scenario. The numbers of such objects are shown, with their color indicating within which area they are located.
6) To attract your attention and give you enough time to see what is happening, the simulation will stop every time an interesting event occurs (e.g., the trip of an agent to another proxy, a Tracker removing or creating Updaters, etc.). You must press a key as many times as needed in order to see that event progressing.