| Application programs that directly use the DL/I interface do so by issuing DL/I calls. Application programs that use the JDBC interface do so by issuing standard SQL (structured query language) calls. Accessing IMS by Using DL/I Calls 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 3-1 on page 19 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 3-1. Example of a Simple Application That Accesses an IMS Database Through DL/I 
Figure 3-1 illustrates the following processing models: Traditional processing model: The objects on the left side of Figure 3-1 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 "Message Format Service" on page 182.
- - z/OS Communication Server: A communications package that is part of the z/OS operating system. In Figure 3-1, IMS is communicating with the Virtual Telecommunications Access Method (VTAM®) function within the z/OS Communication Server.[2]
[2] Although IMS uses the network facilities of VTAM, it can also control devices that use the basic telecommunications access method (BTAM) or the basic sequential access method (BSAM). VTAM is the preferred access method for IMS.
- - 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 computera 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 3-1 on page 19 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. For more information, see "Open Transaction Manager Access" on page 179.
- - 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 "IMS Connect" on page 187.
- - 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 "WebSphere Application Server for z/OS Applications" on page 317.
Figure 3-1 on page 19 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.
Accessing IMS Using JDBC The IMS Java function provides IMS's implementation of the JDBC API. Application programs that use the JDBC interface to access IMS issue SQL calls and might run on a non-z/OS platform. The IMS Java function allows you to write Java application programs that access IMS databases and IMS message queues from many different locations: Within IMS Any environment that supports the JDBC API IBM WebSphere Application Server for z/OS WebSphere Application Server running on a non-z/OS platform IBM Customer Information Control System (CICS) Transaction Server for z/OS IBM DB2 Universal Database for z/OS stored procedures
For more information about writing Java applications for IMS, see Chapter 18, "Application Programming in Java" on page 311. Figure 3-2 illustrates an Enterprise JavaBean (EJB) that can perform work on the IMS checking account database. Notice that in Figure 3-2, IMS does not require an application program to issue DL/I calls. Figure 3-2. Example of an EJB That Accesses an IMS Database Through the JDBC Interface 
Figure 3-2 includes the following components: DL/I. DRA: The database resource adapter (DRA) is the bridge between ODBA and IMS. ODBA: Open Database Access (ODBA) is the IMS callable interface for access to IMS DB. IMS JDBC resource adapter: The IMS JDBC resource adapter that is deployed on the z/OS platform. The IMS JDBC resource adapter is delivered with the IMS Java function. IMS Java EJB: One of two IMS Java-supplied EJBs is the host-side component that facilitates communication with and passes transaction information to the IMS JDBC resource adapter. These EJBs act as listeners for remote requests. WebSphere Application Server for z/OS. IIOP: Internet Inter-ORB Protocol (IIOP) is the protocol that can be used between WebSphere Application Server for z/OS and WebSphere Application Server running on another platform. IIOP allows the servers to exchange data. Data is securely transferred across the Internet using the SSL (Secure Sockets Layer) protocol. IMS distributed JDBC resource adapter: The resource adapter that is deployed on the non-z/OS platform, which contains a type-3 JDBC driver and is delivered with the IMS Java function. EJB: The EJB enterprise application that contains your business logic and is deployed on WebSphere Application Server. WebSphere Application Server: WebSphere Application Server on which the client application runs. non-z/OS platform: The operating system that hosts WebSphere Application Server.
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