The mainframe centered IT environment is still a common architecture in many large organizations, especially in the financial industry. But the increasing demand for new applications and integration of modern communication technology forces a paradigm change. The paper deals with the challenging task of defining and controlling a disciplined evolution of the existing centralized IT systems into a new integrated architecture. First an introduction into the problem domain of large scale IT systems and into the basic characteristics of mainframe computing is provided. Analyzing the characteristics of large scale systems leads to the concept of a managed evolution and a service architecture. The description of requirements for this new architecture is followed by a discussion of design guidelines and a detailed explanation of the mainframe implementation. The paper concludes with up-to-date testing results which prove the scalability of the implementation up to several thousand distributed clients.

The increasing demand for interoperable systems requires the integration of traditional mainframe-based transaction processing (TP) monitors with CORBA-based middleware infrastructures. We discuss various integration approaches. The integration of IBM's IMS-TM (Information Management System Transaction Manager) and CORBA is discussed in detail, and up-to-date performance and scalability results are presented. The results show that the combination of CORBA and mainframe-based TP monitors is significant step towards highly available, highly scalable object transaction monitors (OTMs).

Sather extends the notion of an iterator in a powerful new way. We argue that iteration abstractions belong in class interfaces on an equal footing with routines. Sather iterators were derived from CLU iterators but are much more flexible and better suited for object-oriented programming. We retain the property that iterators are structured , i.e., strictly bound to a controlling structured statement. We motivate and describe the construct along with several simple examples. We compare it with iteration based on CLU iterators, cursors, riders, streams, series, generators, coroutines, blocks, closures, and lambda expressions. Finally, we describe experiences with iterators in the Sather compiler and libraries.