DL/I is a standard interface to IMS functions that has been in place since IMS's inception. Most of the IMS application programs that have been written over the years are still providing the service for which they were designed. As business needs have evolved, these application programs have either evolved or have become a base for new application programs to meet the new business needs. In many cases, the application programs that run today's businesses are not individual programs, but are a number of layers of application programs that work together to implement the businesses' information technology (IT) infrastructure.

To illustrate how IMS business application programs have evolved, Figure 2 shows a simple, hypothetical IMS application program that accesses a checking account database through DL/I. Assume that this application program was written 20 years ago, was written in COBOL, and was designed to support IBM 3270 (non-programmable) terminals. There are many such application programs that still run as originally written and provide this kind of support for the banking industry.

Figure 2. Example of a Simple Application that Accesses an IMS Database Through DL/I

Figure 2 illustrates the following processing models:

• Traditional processing model: The objects on the left side of Figure 2 represent the traditional processing model that includes the following components:
  • DL/I: The interface to the IMS modules that access and manipulate the data in IMS databases.
  • Checking account application program: This program performs basic operations on checking account balances (such as queries and updates) and issues DL/I calls that cause IMS to actually query and update the checking account data that resides in the IMS checking account database.
  • Message Format Service (MFS): A service provided with IMS TM that separates the terminal device characteristics from the application program. For more information, see the complete version of An Introduction to IMS.
  • z/OS Communication Server: A communications package that is part of the z/OS operating system. In Figure 2, IMS is communicating with the Virtual Telecommunications Access Method (VTAM®) function within the z/OS Communication Server⁵.
  • Communications Controller: A device (hardware and software) that is part of the telecommunications network.
  • 3270-type terminal: Before personal computers (PCs) were invented, these terminals provided access to the mainframe computer - a bank teller might use such a terminal. In general, these types of terminals have been replaced with PCs that run 3270-emulation application programs.
• Updated traditional processing model: Figure 2 also shows how the following layers of application programs and protocols have been added to the original application program to enable Web-based personal banking:
  • OTMA: Open Transaction Manager Access (OTMA) is an open interface to IMS TM.
  • IMS Connect: IMS Connect is an optional IMS TM network component that provides high performance communications for IMS between one or more TCP/IP clients (such as, WebSphere Application Server for z/OS) and one or more IMS systems. For more information, see the complete version of An Introduction to IMS
  • WebSphere Application Server for z/OS: A comprehensive, sophisticated, Java 2 Enterprise Edition (J2EE) and Web services technology-based application platform specifically designed to leverage the qualities of service inherent in the z/OS operating system. For more information about how IMS supports WebSphere Application Server for z/OS, see the complete version of An Introduction to IMS.

    Figure 2 includes the IMS Resource Adapter, which is delivered with the IMS Connect function and IBM WebSphere Studio Application Developer Integration Edition.

  • Enterprise JavaBean: A user-written, object-oriented, distributed, enterprise-level application.
  • Web Browser: A client program that initiates requests to a Web server and displays the information that the server returns. The Web browser is the actual end-user interface with which bank customers can manipulate their checking accounts.