You can integrate Windows-based applications with a mainframe using screen scraping. In a session with an IBM mainframe, screen scraping allows data to be sent to, and read from, specific locations on the screen. The two advantages to screen scraping are: it's inexpensive and it easily allows clients to interact with mainframe programs that simply expect data to be filled in at field locations on the screen.
Advanced screen scraping with HTML allows a client on the Web to interact with the mainframe as though it were an attached terminal. Access to mainframe data and programs can be transparent to the user, whether over the Web or from a traditional client/server application.
A Windows-based client program can create its own user interface and, through screen scraping, present mainframe data to a user in an entirely different, graphical way.
While screen scraping was an early boost to accessing mainframes, it falls short of modern access technologies. If screen scraping will satisfy your application's requirements, by all means consider using it. In the long run, you may be happier with using the more sophisticated integrating technologies provided by SNA Server.