Team 6- The Big Endians
The clients (cars) connect to GPS Server and first send the name of their destination street. After that, at regular intervals, they send queries about the next step that they need to go to, in order to reach their destination. The GPS Server gets the car position information from satellite. Using its embedded algorithm, the GPS Server calculates the shortest route that the client can take in order to reach its destination and then returns this next step information to them. The database server stores all the states and session information about each query from different clients.
The system has three types of servers: satellite server, database server and GPS server.
The GPS server is the main server we focus on. Satellite server tells the GPS Server what it observes from the car. The database server stores static map information, the states and session information about each query from different clients.
The following tables describe the details of these servers. Notice that the types of server are more conceptual than physical.
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Satellite Server |
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Description |
This server represents a GPS satellite |
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Functions |
The only function of the satellite server is to detect the position of each client. |
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Type |
It is considered as an external server with 100% reliability and availability. (pretty much like a credit-card info server in E-commerce) |
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Invocations |
It does not invoke any server It gets invoked only by the GPS server |
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State management |
Does not store any state information
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Interface definitions |
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Database Server |
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Description |
This server contains all the information about the different streets in the city |
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Functions |
Database management |
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Type |
It is considered as an external server with 100% reliability and availability.[H1] |
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Invocations |
It does not invoke any server It gets invoked only by the GPS server |
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State management |
Does not store any state information
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Interface definitions |
All the database management will be handled through contained managed persistence |
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GPS Server |
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Description |
This is our main server. Here we will implement the main functionalities of the system. |
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Functions |
Inform the client's current position Suggest the optimal route to reach the destination (return an next step object which contains the next street name as well as other necessary information) Query the satellite server for the position of the car (based on the possible set of streets the client can turn into from the original street) Manages the sessions of its clients |
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Invocations |
It invokes the GPS Satellite It invokes the Database Server It is invoked by the GPS client |
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State management |
For each client it holds: The session ID The entire route to the desired destination The actual position of the client The history movement of all clients in their life cycle |
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Interface definitions |
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The clients in the system are the cars.
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Description |
The client is supposed to be a GPS device located in some vehicle |
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Functions |
The only function of the satellite server is to detect the position of each client. |
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Invocations |
It invokes the GPS server |
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State management |
Does not store any state information
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Interface definitions |
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Some supplement about clients:
· Main purpose: To reach their destination/know their current location
· It invokes the GPS server. Every time it comes to an intersection or every 5 seconds.
· There can be up to 420 clients concurrently logged into the server at any given time.
· If destination address not in database, client needs to select another destination.
· Information lost, the client has to resend the information
The following are exceptions in our system. Notice that we have an assumption in our project is that the system has database integrity, so we need not consider exceptions about no-meaningful data.
· Destination Address not in Database
· Invalid ID
· Conflicting ID
· Satellite Connection Timeout
· Cannot identify next step
· Information Lost
· Cannot connect to satellite
· Cannot connect to database
The following are our interfaces, each of which has some methods.
Route getService(String destination) // Gps server returns a unique id for this client which is a data member of object Route;
Boolean stopService(String id)
Route getNextStep(String id)
Route getRoute(Position currentLocation, Position destinationLocatin )
Position getNewPosition( Position currentLocation, Position [] alternatePosition, Position destinationLocation, String id)
Database
There are two data domains in our database. One is map, the other is client.
· Map domain identifies the information about the map. Two optional designs are offered now. Map information is entity.
· Client domain identifies the information about each session of each client. Client information is session.
-- Design 1 --
In this design, we have only one table and each record in this table represents part of a road between two intersections
[MapTable]
Columns:
ID (primary key)
int Start_Location_x
int Start_Location_y
int End_Location_x
int End_Location_y
String Street_Name
-- Design 2 --
In this design we have two tables (Intersection, RoadName) and each record in the “Intersection” represents an intersection of two roads.
[Intersection]
Columns:
ID (primary key)
int Location_x
int Location_y
int Forward_RoadId
int Backward_RoadId
int Right_RoadId
int Left_RoadId
[RoadName]
columns
ID(primary key)
String RoadName
Columns:
String ID (primary key)
int Current Location x
int Current Location y
int Destination Location x
int Destination Location y
String History
We analyze the architecture of our design; we found the following questions, which need to answered or determined:
· Do we need a 3rd party server?
· Is our flow of events all right?
[H1]I think we cannot say that the
database server is 100% reliable, I suggest to say we don’t deal with the
fault-torrent issue inside the database server.