There are many ways to integrate distributed systems with the mainframe. The mainframe is an odd creature to integrate with because legacy applications were build on proprietary systems (like CICS) and protocols (like SNA). Open systems and more recently Service Oriented Architecture (SOA) make recently developed systems more interoperable.
To understand mainframe integration, you have to understand the underlying data structures. We then can discuss integration techniques and patterns. The data structures are represented in the existing programs written for the mainframe, which are mostly COBOL programs.
