Middleware for z/OS – Application Servers

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There is a large variety of middleware tools available on z/OS. Some are very similar to the software also available on other platforms, like WebSphere Application Server and Db2, and some are only available on the mainframe, like IMS and IDMS. I will highlight a number of the main middleware tools for z/OS in this chapter.

Application Servers

Application Servers are tools that make it easier to run interactive applications. Today we call these tools Application Servers. On the mainframe these tools were traditionally called Transaction Managers. A small intermezzo to explain the similarities and get acquainted with the terminology.

Applications Servers and Transaction Managers intermezzo

Despite their different name, Application Servers and Transaction Managers achieve the same goal: make it easy to build and run interactive applications. Application Servers gather a set of common functions for these types of applications. These functions include network communications, transaction functionality, features to allow scaling of applications, recovery functions, database connectivity features, logging functionality and much more.

For Java a standard for these functions is created in the Java Enterprise Edition (JEE) standard. The z/OS Transaction Managers all provide a similar set of functions, for multiple programming language like COBOL, PL/I, C/C++ and Java.

With a modern web application server, the user enters a url consisting of the name of a server and an identification of the piece of code on that server. For example, a user types in his browser http://acme.com/fireworks/index.html . In this, acme.com is the server name and fireworks/index.html is the piece of code to execute on that server – called the uri. The application server takes the uri, executes the code and returns a response html page.

The traditional transaction managers work in a similar way. First you must make a connection from your terminal to the transaction manager.

Traditionally you did this by typing something like “LOGON APPLID(CICSABC)”. Then you were connected to the application server and you were presented some screen. Then you type in a transaction code. The transaction code is similar to the uri: it identifies which piece of code to run. The transaction manager executes the code and returns a response screen to the user.

The transaction managers on z/OS nowadays can work in both ways. They still have the traditional interface, which is hardly used for business applications anymore, and they also have a modern web application interface like web application servers.

CICS traditional versus a web application server

CICS traditional versus a web application server

Now let’s have a look at what sort of application servers we have on the mainframe.

WebSphere Application Server

IBM’s WebSphere Application Server (WAS) is an application server for Java programs, complying to the JEE Java application standard. WebSphere was one of the first implementations of a Java application server. It was made also available on z/OS.

Initial implementations of WAS on z/OS were very inefficient and had stability issues. After a redesign and the introduction of speciality engines for Java processing (see section Specialty engines), z/OS has become of very cheap platform for JEE applications.


CICS is the most popular Transaction Manager on z/OS. It was designed for COBOL and PL1 applications, but nowadays you can also runs Java applications.


IMS is a transaction manager like CICS, but it also has a database management component. Although less prominent as CICS, quite a number of very large organizations are relying on IMS for their daily core processing.

An interesting fact is that IMS was built for NASA as part of Kennedy’s moon challenge.

IMS has two parts: IMS/TM and IMS/DB. IMS/TM is IMS/Transaction Manager, an application server. IMS/TM is as such functionally similar to CICS. It is also build for COBOL and PL/I, and can now also run Java programs.

IMS/DB is described briefly below.


IDMS is a transaction manager and a network database manager, owned by CA/Broadcom.

IDMS, like IMS, also has an application server and a database manager part. IDMS/DC is the transaction manager/application server part. It looks very much like CICS.

IDMS/DB is a network database management system. See below.


NATURAL is Software AG’s fourth generation application development system that allows you to create, modify, read, and protect data that the DBMS manages. You can have online – like CICS – and batch Natural programs.

Natural usually uses ADABAS. Natural is the application server that uses ADABAS as it’s backend database management system.

IDEAL and Datacom

Another combination of application server tools that is quite common on mainframes is Datacom/DB and IDEAL. The products are now owned by CA/Broadcom.

IDEAL is a 4GL programming environment, designed for the relation database management system Datacom/DB. IDEAL generates COBOL, which runs in CICS, and uses Datacom/DB as a backend store. Although originally built for Datacom/DB, it was later also enabled for IBM Db2.