International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
authorization is required. AgentServer manages a table to 
register other “Agent Regions" that are authorized with itself 
each other. Between two directly authorized *Agent Regions", 
agents between them can communicate via the coordination of 
their AgentServers. The authorization relation in Geo-Agents 
can be passed one by on: If a directly authorized AgentServer 
chain can be found for two “Agent Regions” that have no direct 
authorization, agents between the two “Agent Regions” can 
communicate via the coordination of the AgentServer chain. 
2. COLLABORATION MECHANISM IN GEO-AGENTS 
In human society, there are some relations among individuals, 
which make individual collection become human society, and 
make individuals become socialization people. Just like human 
society, multi-agent system must let its agents cooperate with 
each other to become an integrated system, so as to complete 
more complicated tasks (Hyacinth S. Nwana, 1996; Ding 
Xiaoming and Liu Bogin, 1999). 
The goal of Geo-Agents is to construct a multi-agent system 
like human society, so collaboration mechanism is necessary. 
There are two collaboration modes in Geo-Agents: 
collaboration among interface agents and collaboration under 
control of interface agent. 
2.1 Collaboration among Interface Agents 
Collaboration among interface agents is coordinated by 
AgentServer. AgentServer manages a table to register different 
cooperation groups in one “Agent Region”. There are three 
types of collaboration among interface agents: direct 
cooperation, peer group cooperation and charge-tributary group 
cooperation. 
(I) Direct cooperation: during the execution of an interface 
agent, it needs some results of other interface agents (see figure 
2(a)). 
  
(e) Charge-tributarv Group Cooperation 
Figure 2 Collaboration among Interface Agents 
(IT) Peer group cooperation: several interface agents form a 
team. All team members cooperate to complete a same complex 
task. Each member assumes a subtask, and accomplishes it 
independently. Team members are peer in the team: after 
completing subtask, each member sends its result to all other 
members, so each member can obtain a same final result of the 
task (sce figure 2(b)). 
(II) Charge-tributary group cooperation: like peer group 
cooperation, all team members cooperate to complete a same 
384 
complex task. But there is a team-charger. Team member 
completes subtask and sends its result to team-charger. Team- 
charger assembles all sub-results to final result of the task and 
sends the final result to all team members (see figure 2(c), 
where A is team-charger). 
In Geo-Agents, the collaboration among interface agents still 
has some restrictions: (1) Collaboration exists inside only one 
"Agent Region". Collaboration among different "Agent 
Regions" is not supported now. (2) Each team member can 
communicate with others only once in one group. (3) The result 
type of each team member is same in one group, and all 
members cooperate to complete a same task. (4) In one group 
team, the number of team member is pre-fixed, and no team 
member can join into the team dynamically. (5) 
Communication among interface agents in one group can take 
place only after all team members are joined in. 
2.2 Collaboration under Control of Interface Agent 
After an interface agent accepts a complex task, it will recruit 
some GIS function agents, and then organize them to complete 
the task cooperatively. This is hierarchy collaboration under 
control of interface agent (see figure 3). 
| Interface Agent | — Interface Agent — Interface Agent | 
AC A 
A T A, 
oe E — Create 
Ay A An| — N me Reuse 
  
  
——— Collaboration 
  
Figure 3 Collaboration under Control of Interface Agent 
The hierarchy of agents is similar to human society. Different 
agents play different roles in the system when cooperating to 
complete a same task. Interface agent locates at top-level. The 
up-level agents may create some under-level agents or reuse 
other existing agents to complete subtasks. Those agents who 
belong to a same parent can execute sequentially or 
concurrently. 
In hierarchy collaboration: 1) Facilitator/AgentServer is the 
collaboration coordinator; 2) up-level agents assign subtasks to 
down-level agents and down-level agents return to up-level 
agents; and 3) the results of some agents may be reused by 
others. 
3. PARALLEL MECHANISM IN GEO-AGENTS 
In a multi-agent system, the smallest executing unit is agent, 
and many agents can execute independently and concurrently. 
Geo-Agents likes a kind of cluster parallel system, and parallel 
is performed by GIS function agents. Parallel of GIS function 
agents takes place in collaboration under control of interface 
agent, and exists as three modes: isomorphic cooperative 
parallel, heterogeneous cooperative parallel and exclusive 
parallel. 
(D Isomorphic cooperative parallel: parallel agents are of the 
same type, and each of them completes a subtask of a same 
complex task. Assembling all subtask-results will get the final 
result. Isomorphic cooperative parallel meets two situations: 
one is that all agents process different data resource; the other is 
that all agents process different parts of a same data resource. 
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