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
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
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.
IMS/DB
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
Datacom /DB is a relational database management system from CA/Broadcom.
ADABAS
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.
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
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
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
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
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.
ADABAS and NATURAL
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.
I recently got a question from a collegue. He wanted to transfer an entire PDS in an email to someone else. You can download all the member of the PDS with FTP, zip up all the files and transfer that. But it might be easier to use this trick.
Create a PS from in PDS by using the XMIT command. XMIT is a TSO command that you can use to transfer a dataset to another user, or system, or both.
The trick now to “zip” a PDS with XMIT is to XMIT the PDS to yourself on the same system:
xmit userid.node dsn(dataset) outdsn(outdsn)
This creates the “zipped” PS dataset, that you can send through email. If you download the file to your Mac or PC, makes sure you download it in binary mode.
The receiver can “unzip” the file into a PDS with the accompanying receive command:
In the previous section I explained that green screen interfaces still exist for administrative tasks. But even for these kinds of work there are modern tools with contemporary interfaces. z/OS itself and almost all middleware running on z/OS can be managed with web-based tools, Eclipse-based toolsfor z/OS, or nowadays more and more Visual Studio Code based tools for z/OS. Furthermore almost all administration tasks on z/OS can be invoked from external tools through REST APIs. More and more development and operations functionality will be made available only in this modern kind of tool sets.
The standard Eclipse-based tool for z/OS that you can download for free is called z/OS Explorer. This tool is a desktop client interfacing with z/OS. Many mainframe tools and middleware solutions provide plug-ins for this tool.
Figure – z/OS Explorer
Considering development tools, there are a number of modern options for the mainframe. IBM has developed an Eclipse-based development tool called IBM Developer for z/OS (IDz). The software company Compuware sells a set of tools for mainframe development called Topaz. There are also open source tools and plugins, like the IBM Z Open Editor for Visual Studio.
These modern tools provide a development experience for z/OS applications that is very similar to the experience you have when you develop applications for other platforms, like Java, PHP or Python. Support for developing and debugging mainframe languages such as COBOL and PL/I is supported in the tools, but also Java is supported. As importantly it provides plugins for interacting with middleware such as Db2, MQ, CICS and IMS.
IBM, CA, BMC and other vendors provide many modern tools for the administration of specific middleware in your organization.
Finally, a recent development is the open source project called Zowe. This project is a collaboration of a number of mainframe software vendors and aims to provide an open source software framework for development and operations teams to securely, manage, control, script and develop for z/OS like any other cloud platform.
In separate chapters I will discuss a little bit more on the modern application development and operations architecture tools for z/OS, and on modern monitoring architecture and tools.
