query for complex logic

Table:GRoupAllocation
______________________
GroupId (Primarykey)
GroupName

Table:SystemAllocation
_______________________
SystemId(Primarykey)
SystemName
GroupId (foreignkey)

TableeviceAllocation
_______________________
DeviceId (Primarykey)
DeviceName
SystemId (foreignkey)
_______________________

Table:SensorAllocation
_______________________
SensorId (Primarykey)
SensorName
GroupId (foreignkey)
SystemId (foreignkey)
deviceid(foreignkey)
_______________________

Table:GRoupAllocation
______________________
GroupId GroupName
1 Group1
2 Group2
3 GRoup3
4 Group4

Table:SystemAllocation
___________________________
SystemId SystemName GroupId
1 system1 1
2 system2 2
3 system3 3
4 system4 2
5 system5 1

TableeviceAllocation
___________________________
DeviceId DeviceName SystemId
1 Device1 1
2 Device3 3
3 Device4 2

Table:SensorAllocation
____________________________________________
SensorId SensorName GroupId SystemId DeviceId
1 sensor1 1 1 1
3 sensor3 2 2
4 sensor4 3 3 3

my results should be like this:


Results:
___________________________________________________________________
GroupName SystemName DeviceName SensorName
___________________________________________________________________
Group1 system1 Device1 sensor1
Group1 null null sensor2
GRoup2 system2 null sensor3
GRoup2 system4 null null
Group3 system3 Device3 sensor4
Group4 null null null

so i need to populate the results in treeview.my treeview looks lika this:

Group1
|____System1
|________Device1
|_______sensor1

|_______system5

Group2
|____System2
|________Device1
|_______sensor1


|____System4
|____Device4

like this i need to populate. i need to show all the groupname and belonging systemName and belonging devicename and belonging sensorname

so please give me query for this complex operation please
criteria's
1.GRoup can have systems and system can have devices and device can have sensors
2.GRoup can have systems and systems can have sensors[no device]
3.GRoup can have systems and systems can have devices [no sensor]
4.GRoup can only have system [no device, no sensor]
5.GRoup can have only sensor[no system, no device]
so please

for therefrence i haveattached this in text file. please refer