n 
en the operating 
nd initializing its 
tables, the server 
nts. 
X server with a 
e Figure 3). The 
ins: Delta-X cli- 
the transaction, 
(in case of data 
(in case of data 
entication of the 
t and of the type 
nds an acknowl- 
client and then 
see Figure 3). 
>d in the transac- 
the read and/or 
fied in the lock 
until the data is 
ad transactions: 
ess to unlocked 
read access to 
] check-out read 
ata. 
ite transactions: 
-in which modi- 
lways creates a 
wed only if the 
user. Older, no 
be deleted man- 
the same data, 
ollowing a write 
> all write trans- 
ss accesses the 
an proceed con- 
about the status 
nessages at 
progress of the 
atus messages 
informed about 
it the user can 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
$- 1... 
  
Dx Client Collection 
calling Service 
process 
Dx Client Collection 
Calling Service et. 
Process 
Dx Client Collection 
calling Service 
process 
Delta-X Server 
   
  
  
—] Dx Server's transaction process 
  
  
Transaction 
Monitor 
  
——— PB» Dx Server's transaction process 
  
  
  
p» Dx Server's transaction process 
  
  
  
  
  
Legend: 
  
  
  
ist call: “request for transaction” 
1st return: “acknowledgment of a transaction” 
Initialization of a transaction process 
2nd call: “reply with results” 
  
Figure 3: The Delta-X Client-Server Communication 
make decisions about the further execution of a 
transaction. This is necessary, because a typical 
format conversion can take a few hours to com- 
plete even on a powerful workstation. 
2. The Delta-X client periodically monitors transac- 
tions that it started. 
A single Delta-X server can be accessed by many 
Delta-X clients at the same time. Even a single client 
can start many transaction on the same server. In our 
curent implementation, all conversion processes 
Share the same CPU. The Delta-X server architec- 
ture, however, can also be implemented on a parallel 
machine or on a cluster of workstations on a dedi- 
cated LAN, where each transaction process runs on 
a different machine. All transaction processes share 
the same database. 
4.0 The Delta-X Client 
The Delta-X client is a software module that runs on 
the user's machine and enables Delta-X users to start 
and control data conversion and transfer transac- 
tions. Users can either export their data to or import 
data from a server. The Delta-X client also supports 
administrative functions, such as joining or leaving 
359