• SpADE Client
  A client includes four components.
  • GPS Service Module is responsible for receiving and parsing the GPS information.
  • Map Service Module is responsible for displaying underlying map and moving objects if any, and listening to interaction events from the user.
  • Query Service Module constructs spatial-temporal queries according to user triggered events on the map.
  • Communication Manager sends requests to and receives data from the server.
  
  
• SpADE Server
  The SpADE server comprises five modules.
  • Communication Manager receives query messages or location update requests from the clients, dispatches them to other modules, and returns query results to the client user.
  • Map Service Module maintains the map data displayed at the client side and notifies all clients to update their map if a new map is provided.
  • MOD Service Module processes position updates and query requests from mobile clients.
  • Index Service Module constructs Bx-tree index to facilitate processing spatialtemporal queries.
  • MySQL Database stores the moving objects information in relational table and provides B⁺-tree as the underlying basis for B^x-tree.

• Moving objects are modeled as a linear function of time
• Partition the time axis into intervals of duration t_mu (maximum update interval), and sub-partition each interval into n equal-length sub-intervals, termed phases
  
• Map the update (and insertion) times in the same phase to the same so called label timestamp, t_lab
• Object O = (x, v) updated at tu is represented by a value B^x_value (O, t_u):
  
  B^x_value (O, t_u) = [index_partition]₂ ⊕ [x_rep]₂
  where index_partition is determined by the update time, t_u, and x_rep is obtained using a space-filling-curve:
  
  index_partition = (t_lab/ (t_mu / n) - 1) mod (n + 1)
  x_rep = x_value (x + v (t_lab - t_u))
  

• A relational table in MySQL DBMS is defined to store information about moving clients. The table consists of 7 fields as in following table. The B^x-Value is the primary key of the table and a B⁺-Tree index is built on this field.

*To accomandote the use of the B⁺-tree to index moving objects, a field named B^x_Value into the table of moving object and make it as the primary key indexed by the B⁺-tree.
• In SpADE system, there are two such tables. One is to store the latest update information of the moving objects, called the current information table. Note that this table is indexed by the B^x-Value obtained according to the B^x-tree rationale. The other table simply keeps all the historical information, called the historical information table for further reference.
  

  The SpADE system supports various types of queries such as historical (current/predictive) range and k-NN queries. The typical process of executing such a spatialtemporal query takes several stages, as shown in above Figure.

• On the client side, a user selects the query type and specify query parameters by dialog based inputs or map based stylus actions. Then, a corresponding query request is constructed and sent out to the server.
• Upon receiving a query request, the server side communication part extracts query parameters from it and passes them to the MOD service module. Then SQL statements are composed according to the query parameters and the Bx-tree rationale, and passed to the MySQL query engine via the JDBC connection. Each of such SQL statements specifies a range query on the B^x-value. Inside the MySQL, SQL statements are executed with the aid of the B⁺-tree index to retrieve the data requested. The data then will be returned back along the reversed direction till the client side.