1.4. Location Based System Architecture

Considering the example of searching a Chinese restaurant the information chain from a service request to the answer will be described now and is visualized in the Figure below. The information the user want is a route to a Chinese restaurant near by. Therefore the user expresses his need by selecting the appropriate function on his mobile device: e.g. menu: position information => searches => restaurants => Chinese restaurant.

1. When the function has been activated, the actual position of mobile device is obtained from the Positioning Service. This can be done either by the device it self using GPS or a network positioning service. Afterwards the mobile client sends the information request, which contains the search goal and the position via the communication network to a so called gateway.
2. The gateway has the task to exchange messages among mobile communication network and the internet. Therefore he knows web addresses from several application servers and routes the request to such a specific server. The gateway will store also information about the mobile device which sends the information.
3. The application server reads the request and activates the appropriate service - in our case a spatial search service.
4. Now, the service analyses again the message and decides which additional information apart from the search criteria (restaurant + Chinese) and the user position is needed to answer on the request. In our case the service will find that he needs information on restaurants from the yellow pages of a specific region and will therefore asking for such data from a data provider.
5. Further the service will find that information on roads and ways is needed to check if the restaurant is reachable (e.g. sometimes a restaurant on the other river side might not be reachable since no bridge is near by).
6. Having now all the Information the service will do a spatial buffer and routing query (as we know from GIS) to get some Chinese restaurants. After calculating a list of close by restaurants the result is sent back to the user via internet, gateway and mobile network.

The restaurants will now be presented to the user either as a text list (ordered by distance) or drawn in a map. Afterwards the user could ask for more information on the restaurants (e.g. the menu and prices), which activates a different kind of services. Finally if he has chosen a specific restaurant he can ask for a route to that restaurant.