Thesis - Instituto de Telecomunicações

40 CHAPTER 3. INFORMATION SOURCESField Bytesmessage ID 1event ID 1DOM-Object ID 1relative position X 2relative position Y 2absolute position X 2absolute position Y 2other information 4timestamp 4Table 3.2: WIDAM data message.ID is the number associated to the generated event (see table 3.1). The document objectmodel object ID is the number that identifies the object in the page that is connected tothe event. The relative positions are the x-axis and y-axis displacements relative to theorigin of the DOM object.The absolute positions express the pointer position relativeto the page origin. The other information field contains additional data. In the caseof an onKeyPress event the other information contains the American Standard Code forInformation Interchange (ASCII) value of the pressed key. The time stamps indicate, withmillisecond precision, the time when the event occurred.We can compute the approximate bandwidth required by the protocol by measuring adata message and the messages exchange frequency. Input devices, such as the keyboardand the mouse, generate the messages. The pointer movement is the source of most of themessages. It sends events notification every time the mouse is moved. The pointing deviceis usually sampled at 50 times per second (there are some differences between operatingsystem and types of mouse, but these values are similar). We will need an approximately 1kbytes/s (950 bytes per second) as the maximum required bandwidth. This value occurs inthe worst case of the user being always moving the mouse (without any interruption to clickor read), which is not the typical situation. Even at the maximum required bandwidth, theprotocol doesn’t require more than a simple Internet phone line connection.ExampleWe used the WIDAM system in the context of HiMotion project to monitorthe user activity while doing the cognitive tests. One of the games is presented in figure 3.2,the memory game. A person clicks in a hidden image that reveals itself and then tries tomatch the pair image that exists somewhere in the board. If the match fails, both images