Operating Systems

Code reuse is a key concept I learned in college-level programming classes. The technique initially was used when coding subroutines in programs. It evolved to using the inter-program communications feature of a programming language to write separate programs that could be used from the main program. The result was the ability to build a set of tools that could be used by any future program written. This practice remains prevalent today, and programmers usually have an arsenal of callable programs that perform some function that’s integral to their systems.

Web Services Background

As client/server systems became vogue, inter-program communications evolved to inter-systems communications over a network. This evolution took various forms, including:

  • The Open Group’s Distributed Computing Environment (DCE) architecture - Remote Procedure Call (RPC), which Sun developed as part of its Open Network Computing (ONC) architecture
  • Microsoft’s Component Object Model (COM) and Distributed COM (DCOM), modeled after the RPC in DCE
  • The Object Management Group’s Common Object Request Broker Architecture (CORBA).

DCOM and CORBA are somewhat limited in that the same implementation of each protocol is typically needed to communicate between systems. For DCOM, this means Windows; for CORBA, each system requires the same ORB broker.

Web Services is an implementation of an overall concept called Service-Oriented Architecture (SOA). Since Web Services is based on open standards, it compensates for some of the weaknesses in DCOM and CORBA. An SOA can be implemented in many ways; for instance, both MQ Series and CICS Transaction Gateway can be considered an SOA. An SOA is more commonly thought of as being tied to Web Services. In turn, Web Services is usually thought of in terms of the implementation called Simple Object Access Protocol (SOAP). (A full description of SOAs, Web Services, and SOAP is beyond the scope of this article. For more information, see the resources listed at the end of this article.)

In Web Services, the “service” (a.k.a. provider) provides a specific function. The consumer uses the service and requests it from the provider. The provider implements the service for any consumer that wishes to use it. The service implementation is transparent to the consumer; the consumer doesn’t care how the provider implements the service. The consumer and provider can be running any operating system and can implement their respective roles in any programming language. These details aren’t known, nor are they divulged each to the other. Service implementation can be a simple mathematical calculation or a complex operation involving file or database operations or even invoking other Web Services. The communications between the provider and consumer is through HTTP-based request and response messages.

The interface used for Web Services and SOAP, in particular, are standard HTTP messages (SMTP is also supported), the same HTTP used to communicate with Websites. The messages are entirely composed of XML. Two additional standards used with Web Services are Web Services Description Language (WSDL) and Universal Description, Discovery and Integration (UDDI). WSDL is used to describe a Web Service, what parameters it requires, and that responses should be expected. UDDI is used to advertise a Web Service.

The VSE Implementation

The VSE/ESA e-Business Connectors provide the SOAP server, SOAP client (including the HTTP communications client) and XML parser (used to translate messages between CICS and the Web Service). Designed to be used under CICS Transaction Server for VSE/ ESA 1.1.1, it’s available with VSE/ESA 2.6 +APAR PQ78973, VSE/ESA 2.7, and z/VSE 3.1. Regardless of the release of VSE you’re running, you should check with the support center to determine if any additional service is required.

The VSE e-Business Connectors’ Website provides a wealth of information on how each of the connectors works. The SOAP connector is no different. Unfortunately, all the code examples are in C. That shouldn’t be too intimidating, but nonetheless, you like to see examples that match as closely as possible the situation you’re going to try to re-create.

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