any commercial 
ct-oriented. The 
in Delta-X sery- 
latabase servers 
cal schema, and 
ata. The internal 
r Server is trans- 
eration. A sepa- 
pts each internal 
a interface used 
es are GIS-spe- 
1es and the data- 
Delta-X that are 
/Stems. 
ita storage func- 
data processing 
y facilitates data 
ganized applica- 
t also enables us 
lopment in both 
or example, the 
-X prototype can 
hout any impact 
n fact, different 
itabase manage- 
ist in a Delta-X 
ach other. Simi- 
e of GIS without 
interchange for- 
allow different 
cessing systems 
 Delta-X federa- 
imework of 
in a Delta-X cli- 
Delta-X servers 
; conversational 
llows. A client 
action, and then 
| the server fin- 
when it has to 
rver connects to 
ta or reports the 
1e asynchronous 
a-X is the long 
transactions. À 
purs to complete 
  
and it would not be reasonable to maintain a connec- 
tion between a client and a server and thus tie up 
network resources for the whole duration of the 
transaction. 
The asynchronous communication between the 
server and the client has several other advantages. 
First, the server can simultaneously process multiple 
transactions from multiple clients without running 
out of communication channels. Second, asynchro- 
nous communication between Delta-X entities facil- 
itates nesting and chaining of Delta-X transactions. 
For example, a client may request a transaction from 
a certain server. The server starts the transaction and 
once in a while connects to the client to deliver a 
report on progress of the transaction. When the 
transaction migrates to another server, for example, 
to perform a special conversion, the new server will 
also connect to the client in the same way to deliver 
status reports and eventually the results. The client 
does not have to tear down the connection to the old 
server and establish a connection to the new server. 
However, the client must be informed by the servers 
that the transaction has migrated so that it knows 
where to send inquiries about the transaction. 
WAN / LAN 
The implementation of client-server and server- 
server asynchronous communication is based on the 
SUN remote procedure calls over TCP/IP. 
3.0 The Delta-X Server 
The Delta-X server is a node in a network of Delta- 
X hosts which has a data repository containing a part 
of shared data stored in the Delta-X federation. The 
Delta-X server performs the following functions: 
1. Transaction management and surveillance 
2. Data storage, access, and management 
3. Data conversion 
4. 
Client-server and server-server communication 
over a LAN or WAN 
5. Naming and authentication for Delta-X clients 
The Delta-X server comprises modules shown in 
Figure 2. The modules are: the Transaction Monitor, 
multiple Data Conversion modules, the Data Mover 
module, the Delta-X database management module, 
and one or more optional specialized GIS server 
modules to perform functions that are specific to 
that particular GIS. For example, a part of the con- 
version into ARC/INFO format must be performed 
on the ARC/INFO GIS system itself. The GIS server 
Delta-X - Server 
  
  
  
  
  
Delta-X - Server 2 
  
  
  
  
Data Mover | 
  
  
  
  
   
  
Delta-X - Client 
  
  
  
  
  
Transaction 
Monitor 
  
  
Specialized Server | 
Im dm. 
  
Delta-X-DBMS 
  
  
  
     
  
Data 
Conversion 
Module 
Ndi 
  
  
  
  
  
  
  
  
“enon 
  
Figure 2: The Delta-X Server 
357