Database Poller to start the control flow

Question

I am relatively new to BPEL/SOA. I need your help in the design process
I have a design as following:
I have to essentially bring data from DB2 database into Siebel. On the Siebel side I have the Webservices created.
1. rowid, tablename, isTheRowProcessed, timestamp.is the structure of my polling table's structure.
The tablename column will tell me which application table has been updated/inserted with new data.
2. The Database Poller will poll the Polling table every minute and see there is a new row. The BPEL will read the tablename column and fetch the name of the table.
3. Depending on the name of the tablename, a specific Web Service will be invoked which will insert the data into the Siebel system.
for example, if the new row is:
10 TableA NotRead 8/19/2012 10:10:10
The poller should the read above and make it "10 TableA Read 8/19/2012 10:10:10"
Then WebServiceA should be invoked with some data.
Here is My question:
Should it be Async BPEL process or Synchronous process that should have the Poller?
Will Poller kick start sub BPEL processes?

Answer 1

I have a DB poller which has only one row (always just one row) and the Poller would update flag to N from Y.
The DBPoller is set to run every two seconds. I have a flag that is initially set by human to Y. The Poller will flip the value of the flag to N (from Y) and initiate a one-way BPEL process and if the BPEL process will set the Flag back to Y if successful. If the BPEL process fails then the BPEL process will leave the value of the flag to N and the BPEL process sends a mail to the users about the failure. The users after fixing the issue (may be some of the Web Services called by the BPEL are unavailable), will set the flag to Y and the process will continue.
The above intention is supposed to create create an instance id only after entire BPEL is executed. The poller is configured to execute every 2 seconds.
instance_id starttime BPEL Execution time
1 5:00:00 30 seconds
2 5:00:02 20 seconds
3 5:00;04 25 seconds
The above is the scenario is my current execution.
I thought that the second instance would start at 5:00:30 because the flag value would be N from 5:00:00 to 5:00:30 and the BPEL process would set the flag's value to Y at the end of execution of the BPEL process (instance 1). But, to my surprise 2nd instance is starting at 5:00:02 (just because the poller is configured to run every 2 seconds). Even if the poller is configured to run every 2 seconds the poller should not create BPEL process because the Poller at 5:00:02 should see the flag value of N (The poller should only create an instance if the flag's value is Y).
Please clarify this behavior.