Our project has a number of ASP.NET applications that we'd like to invoke (bring up an ie instance of the page) and pass some data to it.  I'm trying to analyze different thoughts on how to do this (in which would make sense for our current situation).  

The first thing that popped in my head was passing via query string however there will probably be too much data for that.  None of the data is classified as "sensitive".  I wouldn't think we could store it in session since we're invoking a new browser instance entirely either.  I really appreciate the communities thoughts.  Thanks!

Just wanted to add that I did look at http://forums.asp.net/t/1435685.aspx but it doesn't really do what I'd need.

Where is the data coming from that you want to pass to the sites?  The answer (or suggestions) I am thinking about will depend on where the data originates.  Also, are you using this data to populte your .aspx page, and must it then persist between pages?

Use an Ajax panel and webservice to update what ever part of the page application

System A is the main system and B being the system that is getting called.  Basically the data passed from A would drive what is shown on B.  B would then create data that I'd like to have passed back to A.  I'd like to couple it as loosely as possible.

The data originates on system A but is interested in the response back from system B. 

 Well I guess what I was getting at is what type of system are A & B?  Is one a database and another an ASP.NET app?  Are both ASP.NET apps that are open and running and you want to pass data back and forth?

If the answer is the latter, you are going to need (or should use) some intermediate to store the data to pass back and forth like a datbase, xml file, or service that brokers and possibly stores the data too.  I hope that system 'A' is not a web app that has to reamain open to do some operations in order for 'B; to receive its data.  In this case you may want to move that logic from system 'A' into a web service, WCF service, or windows service (if there is no UI unteraction) as opoosed to an app that must remain open.

I want to offer more specific advice, but it is difficult to offer a more specific solution without knowing what type of systems you are dealing with that need to pass data back and forth.

Ah got yea.  To put it in better context, A is a vendor .NET application and B is a .NET application that we manage.  The vendor would do the "recommended" changes to A based on how we want the transaction to occur.

So unfortunately it is the latter.  System A starts a whole business workflow and retains all of the origination data.  The workflow can not complete until some elements are recorded from System B.  Ideally information from System A would hydrate some of that on System B and then some additional information is entered to drive a couple calculations that need to come back to System A. 

I'm reluctant to say "calculations" because it seems like a quantifiable business process that could be consumed in a service.  Unfortunately this is a belabored process that takes in numerous qualitative and quantitative values through multiple screens and selections.  Refactoring system B into a web service and rewriting the qual decisions in System A is entirely out of scope for this project. 

Thanks for the responses!

Both ASP.NET web apps 

 Ok now I got you, and that makes sense.  It is actually a common scenario and I too have come up against that.  There are several ways to go about asking System 'A' (the vendor system) to provide you with data, so that you can use it in your system 'B' (correct me if I am wrong on that statement).

At this point is nice that your vendor will actually work with you on how you can consume thier systems data; normally it is more of a dictatorship and it is told to consumers how to get the data and that is that. 

The 1st (and maybe not reccomended, but used often) way of getting that workflow data would be for the vendor to export thier data into either a flat file or XML file (preferrable) that you could import when needed to your system.  You could automate bringing in the data into your database or directly to ASP.NET via FTP, a SQL Server Job, or a Windows Service that monitors a directory with a FileSystemWatcher and when a new file is added, the service runs and imports the data.  The other difficult issue with this methoid is the communication is mostly 1 way.

The 2nd (and more preferred) would be to build a new intermediate service (WCF or .asmx) that allows your app to call, and the vendors app to respond with the data real time.  A very basic example of this would be how some weather services work.  Think if I built a custom .NET app that wants to display weather info from a vendors app (i.e. weather.com).  I would hit thier service requesting the data, and weather.com's data (or vendor data for your example) would be passed back for my app to consume.  In your case you could talk back and forth via the service to complete the process since some of system A's process can not be completed until System B has done some work as you mentioned.

I would not be intimidated by creating a service for the apps to communicate dat back and forth.  It will just be up to you and the vendor to agree on the way the service is built and consumed, so you can pass data to each other.

Other than that I don;t think there is a simple 'link 2 web apps and go' solution and using the querystring might work if you have a secure handshake between the (2) sites, but if the data is too large that option is not as workable.

I hope this offers some help to you!

I really appreciate the effort in your responses.  I was somewhat thinking that at time of post but you have given me more insight as to why I might want to go that way.  Thanks!  I'm going to leave the question up for another day or two to see if anyone else has an opinion by chance.