I am looking to write an application that will take client data from a database, transfer it to our server application, manipulate that data and then pass it back to the client. I would like this to be as seamless as possible and as secure as possible. Also, the manipulation part of this could take several hours. The format of the data will be different for each client. To make the application as easy to maintain as possible, the simplest solution too.
What methods would people recommend for achieving this?
WCF will make your implementation easy. It looks like you are wanting to have the client -> server -> client communication asynchronous, since the server process can take hours, you don’t want to block your client that long.
You probably want to define a server WCF service contract to allow the clients to load data to the server. You also want a client side WCF service contract that the server can use to send the results back when the processing is completed. OR you can have the server send a small message to the client WCF service telling it that “results are ready, come and get them when you are ready”. You will need to coordinate this with some type of ID; the server tells the client to use this id when it wants to collect the results.
Have a look for duplex, asynchronous and peer-to-peer communication topics in WCF. There should be plenty of examples if you google around.