Integrating z/OS applications with the rest of the world

Many mainframe applications were built in an era where little integration with other applications was needed. Where integrations were needed, this was mostly done through the exchange of files. For example, for the exchange of information between organizations.

In the 1990s the dominance of the mainframe applications ended and client-server applications emerged. These new applications required more extensive and real-time integrations with existing mainframe applications. In this period many special integration tools and facilities were built to make it possible to integrate z/OS applications and new client-server applications.

In this chapter I will highlight categories of these integration tools that are available on z/OS, from screen-scraping tools to modern integrations supporting the latest REST API interfaces.

File interfaces

The mainframe was designed for batch processing. Therefore integration via files is traditionally well catered for and straightforward.

You can use multiple options to exchange files between applications on z/OS and other platforms.

Network File System

Network File System (NFS) is a common protocol that you can use to create a shared space where you can share files between applications. Although it was originally mostly used with Unix operating systems, it is now built into most other operating systems, including z/OS. NFS solutions however are usually not a preferred option due to security and availability challenges.


The File Transfer Protocol (FTP) is a common protocol to send files over a TCP/IP network to a receiving party, and it is also supported on z/OS. With FTP a script or program can be written to automatically transfer a file as part of an automated process. FTP can be made very secure with cryptographic facilities.

FTP is built into most operating systems, including z/OS.

Managed File Transfer

Managed file transfer is also a facility to send files over a network, but the “Managed” in the category means a number of additional features are added.

Managed file transfer solutions make file transfers more reliable and manageable. A number of additional operational tasks and security functions related to file exchange are automated. Managed file transfer tools provide enhanced encryption facilities, some form of strong authentications, integration with existing security repositories, handling of failed transfers with resend functionality, reporting of file transfer operations, and more extensive API’s.

On z/OS a number of managed file transfer tools are available as separate products: IBM has Connect:Direct and MQ-FTE, CA/Broadcom has Netmaster file transfer and XCOM, BMC provides Control-M  and there are other less commonly known tools.

Message queueing

Message queuing is a generic manner for applications to communicate with each other in a point-to-point manner. With message queuing applications remain de-coupled, so they are less dependent on each other’s availability and response times. Applications can be running at different times and communicate over networks and systems that may be temporarily down. As we will see in the next section, when using alternative point-to-point protocols like web services, both applications and intermediate infrastructures must be available for successful application communications.

The basic notion of message queuing is that an application sends a message to a queue and another application asynchronously reads messages from that queue and (optionally) responds with another message over a queue. Besides the specific asynchronous nature of message queuing, a big advantage is that it can assure message delivery: messages will not get lost, and when the infrastructure is not available, messages remain stored until they can be delivered.

IBM’s MQSeries, or WebSphere MQ as it is called now, is a separate is one of the most well-known and robust solutions for message queuing available on z/OS.

The open API for messaging called Java Message Service (JMS) is implemented by WebSphere MQ and WebSphere Application Server on z/OS.

Applications using Message Queuing

Web services (SOAP, REST)

Web services is the modern technology that enables applications to communicate over the web protocol HTTP, the protocol we also use for browsing the web.

SOAP and REST are two different types of web services. SOAP is a bit older and exchanges XML messages. XML is more resource intensive because handling XML is a complex operation. REST is more modern and lightweight, and today’s API economy is mostly based on REST APIs.

The benefit of integration with web services is that no special infrastructure is needed for applications to integrate, apart from a capable web application server. Integrations are lightweight and can be very loosely coupled.

The downside of web service is that the HTTP protocol does not guarantee message delivery (as opposed to message queueing as we have seen above). Applications using web services have to implement their own recovery and retry mechanisms to cope with situations where connections are lost.

On z/OS today, most modern versions of application middleware on z/OS, like CICS, IMS, WebSphere Application Server, IDMS, and others support REST and SOAP interfaces.

Applications using Web Services

Enterprise Service Bus

Another form of integration can be achieved through Enterprise Service Bus tools. These tools probably give the widest variety of integration options. They can receive and send service requests over a number of different protocols. They can convert messages from and to many formats. And they can orchestrate complex message interactions between multiple applications. Enterprise Service Bus products in the market are Tibco Substation ES and IBM Integration Bus.

ESB solutions can be implemented on z/OS itself, which than often has the advantage of easier integration with the z/OS application side, but also a non-z/OS platform and integrate with z/OS agent software.

Enterprise Service Bus


In many situations it may not be possible to refactor your old mainframe applications. The applications may not be designed properly in a layered manner, middleware technology may have limited options, skills may not be available, or the risk of a changing existing applications is too high. Or there may be other reason you do not want to touch the code.

For these situations, application adapters can help in opening up applications. In general, an adapter converts a proprietary middleware protocol like a CICS, IDMS or IMS API into a more common API or generic protocol, like a Java program, a web service or message queueing interface. Some adapters provide the option of converting a proprietary 3270 screen interface into a neat API through screen scraping.

I will highlight a number of the type of tools here.

Generic functioning of an adapter

CICS Transaction Gateway

CICS Transaction Gateway provides an API for Java and C programs to call a CICS transaction on z/OS.

CICS Transaction Gateway provides only a way to call functionality in CICS, but there is no possibility in this tool to reversely invoke an external program from CICS. CTG is only meant for external programs to call CICS.

CICS Transaction Gateway adapter

IMS Connect

IMS Connect provides a Java API through which you can invoke IMS functions form Java programs. Through IMS Connect you can access IMS transactions as well as data in IMS DB (see section Middleware for z/OS). As such it functions quite similar to CTG, although the native interfaces are of course different.

z/OS Connect

A recent product from IBM is z/OS Connect. This tool converts a REST API into one or more proprietary backend protocols, like a CICS or IMS transaction or call to Db2. Also, z/OS Connect makes it possible to call REST APIs from mainframe applications.

Thus, z/OS Connect provides a bi-directional adapter for REST API through which you expose and call RESTful APIs from existing z/OS programs in CICS, IMS, Db2, WebSphere Application Server and MQ.

z/OS Connect adapter

Screen scraping tools

You may have old legacy applications that are built as a silo, have only 3270 user interfaces and no decent program interfaces.

For this problem, screen scraping tools can be a last resort.

The integration problem of an application silo – refactoring is the ideal solution

A screen scraping tool provides the ability to simulate the interaction of a business user behind a screen, with the old application’s user interface. The screen scraper tool automates the workflow of the end-user by filling in the old application screen programmatically. With these automations such a tool can then aggregate and expose these interactions into higher level services. These higher level services can then be invoked through a modern API, such as a web service by other applications in your organization.

Integration with a screen scraping solution

The big problem with screen-scraping integrations is that you end up with more development artefacts that you need to maintain. Not only do you have the old application to maintain, but now also need to manage the screen scraping middleware and logic.

Screen-scraping should be considered a (very) temporary solution for a serious issue in your application landscape. Such a solution should be replaced by a strategic integration or new application as soon as possible.

Products like HostBridge, Rocket LegaSuite and IBM Host on Demand provide screen scraping facilities.

Legacy integration suites

There are many integration tools on the market that provide one or more of the forms of adapters that I have discussed in the above. For example, GT Software and Oracle Legacy Adapter provide functionality to bridge native z/OS interfaces including screen interfaces to and from modern applications.

Database access via JDBC, ODBC

So far, we have discussed application integration through application interactions – applications calling one another.

Applications on non-z/OS platforms alternatively can directly access data in databases on z/OS through the standard data access protocols ODBC and JDBC. All suppliers of database software for z/OS that I know provide drivers for ODBC and/or JDBC.

Integrating with JDBC and ODBC

From an architectural perspective it is not a preferred solution for integrating applications. Applications should manage their own data and access other applications’ data only through service interfaces, and follow the principle of loosely coupling for application architectures.

Middleware for z/OS – Database management systems

  • Post category:Db2DBAOTM
  • Reading time:3 mins read

In the previous post I started the first part of describing the middleware tools available on z/OS, kicking off with the available application servers of transaction managers.

In this part I will discuss the database management systems that can run on z/OS.


Db2 for z/OS is the z/OS version of IBM’s well-known relational database management system. It is a regular high-end RDBMS, except that it exploits the sysplex capabilities of z/OS.


IDMS/DB is the network database management system com CA/Broadcom. A network database uses special concept to organize data, namely in the form of a network of relationships. Besides some modelling advantages this way of data access can be extremely fast, but as for hierarchical data models like in IMS, it is more difficult to program for it.


IBM’s IMS/DB is a hierarchical database management system. Data in such a database management system is not structured in this database in tables like in Db2, but in tree-like hierarchies. In Db2 and other relational databases there is the well-known SQL language to access data, in IMS you have a language called DL/I to manipulate data.

The hierarchical data model has some modelling advantages and also data access is extremely fast and efficient. The drawback of it is that it is more complex to program.


Datacom /DB is a relational database management system from CA/Broadcom.


ADABAS is Software AG’s database management system. ADABAS organizes and accesses data according to relationships among data fields. The relationships among data fields are expressed by ADABAS files, which consist of data fields and logical records. This data model is called an inverted-list model.

Middleware for z/OS – Application Servers

  • Post category:DBAOTM
  • Reading time:6 mins read

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 . In this, 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.