Introduction

Informix 4GL (I4GL) is a rapid development tool that provides easy language support for creating applications for Informix databases. With the introduction of I4GL v7.50, you can publish your I4GL legacy code as a Web service, thus enabling your I4GL applications to be accessed from client applications.

This is the second of two developerWorks articles explaining how to use I4GL v7.50 Web deployment and subscription features. The article "Deploy 4GL functions as Web services" (developerWorks, February 2009) explains how to deploy I4GL functions as Web services, and provides insights into Service-Oriented Architecture (SOA) and I4GL usage in an SOA environment. This article builds upon that information and explains how to subscribe to a Web service using an I4GL subscriber.

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I4GL as a service consumer in an SOA environment

Service-Oriented Architecture (SOA) is an architectural style that provides methods for allowing different applications to exchange data with one another. It aims at a loose coupling of services with operating systems, their programming languages, and other technologies with underlying applications.

SOA enablement on I4GL is an innovative attempt to ensure the maximum use of legacy business logic by a wider set of applications within and outside an organization. I4GL v7.50.xC2 (released in December 2008) enabled users to publish their existing business logic written in I4GL as Web services; these Web services can then be consumed by any programming language or application. The v7.50.xC3 (released in May 2009) takes this SOA initiative a step further by enabling consumption of Web services using I4GL.

Prior to v7.50 SOA enablement, I4GL developers were faced with challenges in integrating business logic and applications written in I4GL with other modern applications and languages. In addition, organizations seeking flexibility and inter-operation of code written in multiple languages across diverse locations had only one option—to rewrite the I4GL code using a newer technology.

The I4GL-SOA subscriber architecture relies on a user interface (in other words, W4GL). The users obtain the information of a Web service from a Web service definition file and provide the details in the W4GL interface. The W4GL interface generates and stores all these details in a configuration file. The W4GL interface supplies the configuration file as an input to a back-end script (in other words, W4GLC). The W4GLC tool generates intermediate client code to subscribe to a Web service.

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Prerequisites

You must have one of the following platforms to be able to consume Web services using Informix 4GL:

• HP-IA 11.23 / 11.31 (32/64-bit)
• Red Hat Enterprise Linux® 4 or 5
• Solaris 5.9 / 5.10 (32/64-bit)
• SUSE Linux Enterprise Server 10

Your system must also have the following software:

• Apache Axis2/C, Version 1.5 (bundled with Informix 4GL C Compiler implementation)
• Apache Axis2/Java™, Version 1.3.1 (bundled with Informix 4GL C Compiler implementation)
• IBM Informix Dynamic Server, Versions 10.00, 11.10, or 11.50
• Informix 4GL 7.50.xC3
• Java Runtime Environment (JRE) 1.5 or later
• Perl 5.8.8 or later

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Setting the environment

Table 1 outlines the environment variables, which must be set as described:

Configuration file

The configuration file contains the details of the Web service definition generated by the W4GL tool. The configuration file example in Listing 1 below is based on the options the options shown in Figures 3 through 5:

[SERVICE]
   TYPE = subscriber
   I4GLVERSION = 7.50.xC3
   TARGET_DIR  = /tmp/zipcodedemo
   I4GL_FUNCTION = cons_ws_zipcode
   TARGET_FILE = cons_ws_zipcode.c
   [WSDL_INFO]
       WSDL_PATH = /tmp/zipcodedemo
       WSDL_FILE = zipcode_details.wsdl
       WSDL_NAME_SPACE= http://www.ibm.com/zipcode_details
       [FUNCTION]
           SERVICENAME = ws_zipcode
           NAME = zipcode_details
           [INPUT]
               [VARIABLE]NAME = pin TYPE = CHAR(10)[END-VARIABLE]
           [END-INPUT]
           [OUTPUT]
               [VARIABLE]NAME = city TYPE = CHAR(100)[END-VARIABLE]
               [VARIABLE]NAME = state TYPE = CHAR(100)[END-VARIABLE]
           [END-OUTPUT]
        [END-FUNCTION]
    [END-WSDL_INFO]
[END-SERVICE]

The tools

You can use either the w4glc or the w4gl tool to auto-generate the code required to consume a Web service using an I4GL program.

The w4glc tool

This command-line tool is used to generate the code required to establish a connection with the Web service. The w4glc tool expects a configuration file as an input. Advanced I4GL developers familiar with the configuration file syntax may want to use the w4glc tool for faster generation of code.

w4glc { [-silent] [-generate] [-compile] } <configuration_file>

• silent suppresses all the messages from the compiler.
• generate generates the client source code.
• compile compiles the generated source code and creates object files.

W4GL tool

As described in the article "Deploy 4GL functions as Web services," the W4GL tool manages data within the program design database. It also provides options to package individual Web services so that services can be relocated to another machine of the same configuration and platform. Once the data is available in the database, the same service can be generated for various platforms using W4GL on those respective platforms.

The W4GL tool also provides the interface to generate configuration files and generates necessary intermediate C language code required for subscribing to a Web service.

The W4GL tool subscriber option menu is displayed in Figure 2:

Consider the following advantages of using the W4GL tool:

• It takes care of the end to end process of Web service consumption, which includes auto-generation of the configuration file and the corresponding consumer code in C language.
• The WSDL definition specified through the tool is saved in database tables and hence is available for future reuse and modification thus reducing development effort.
• The tool uses a familiar I4GL character based interface to accomplish the consumption task in four easy steps:
  1. Add a Web service.
  2. Generate a configuration file and the intermediate consumer C code.
  3. Make a call to the function in the auto-generated code to subscribe to the Web service.
  4. Compile the sources to create an executable, and run the executable.

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Add a Web service

To subscribe to a Web service, you must first add a Web service definition by selecting Subscribe > Add.

Figure 3 is an example of an Add screen for a Web service named ws_zipcode:

The Subscription ID field is a unique identification number generated by the w4gl tool to track the Web service definition.

The detailed descriptions for the other fields can be found in Table 2.

Figure 4 is an example of a Variable screen for the input and output parameters of the ws_zipcode Web service:

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Generate the configuration file and subscriber client code

Web services information is compiled in a two-step process. In the first step, the w4gl tool creates a configuration file to be used by the w4glc tool. In the second step, the w4glc tool creates the intermediate C language code and compiles it to generate object files in the target directory specified by the user.

Figure 5 is an example of a Subscribe screen used to generate the configuration file:

Figure 6 is an example of a Subscribe screen used to generate the client code:

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Call the Web service using an I4GL program

The zipcode_details function is deployed as a Web service called "ws_zipcode":

FUNCTION zipcode_details(pin)
    DEFINE recdtls RECORD
            pin CHAR(10),
            city CHAR(100),
            state CHAR(100)
        END RECORD, 

        pin CHAR(10),
        sel_stmt CHAR(512); 

    LET sel_stmt= "SELECT * FROM statedetails WHERE pin = ?";
    PREPARE st_id FROM sel_stmt;
    DECLARE cur_id CURSOR FOR st_id;
    OPEN cur_id USING pin;
    FETCH cur_id INTO recdtls.*;
    CLOSE cur_id;
    FREE cur_id;
    FREE st_id; 
    RETURN recdtls.city, recdtls.state
END FUNCTION

The client executable makes the call to invoke the Web service:

MAIN
    define retVal int;
    let retVal = func_cons_ws_zipcode();
END MAIN

FUNCTION func_cons_ws_zipcode()
    DEFINE recdtls RECORD
                pin CHAR(10),
                city CHAR(100),
                state CHAR(100)
            END RECORD;

    call cons_ws_zipcode("97006") returning recdtls.city, recdtls.state
    DISPLAY "SUPPLIED ZIP CODE: 97006 \n"
    DISPLAY "RESPONSE FROM WEB SERVICE \n"
    DISPLAY " ------------------------- \n"
    DISPLAY " CITY:",state_rec.city
    DISPLAY "\n STATE:",state_rec.state
    return 1
END FUNCTION

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Compile the sources to create an executable, and run the executable

The AXIS2/C receives the requests and invokes the Web service ws_zipcode, which then invokes the 4GL function zipcode_details and contacts the IDS server to get the corresponding city name and state name for the zip code.

c4gl clsoademo.4gl cons_ws_zipcode.o -o zipcode_client -
I${AXIS2C_HOME}/include/axis2-1.5.0 -L${AXIS2C_HOME}/lib -laxis2_engine -
laxutil -laxis2_axiom

Run the executable (zipcode_client). The return values are communicated back to the client executable.

./zipcode_client

SUPPLIED ZIP CODE: 97006
RESPONSE FROM WEB SERVICE 
    -------------------------
    
    CITY:Beaverton
    
    STATE:OR

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Conclusion

Enabling I4GL as a service consumer allows you to leverage and reuse existing Web services and business logic coded in I4GL or other programming languages. Enabling I4GL as a service consumer opens up many possibilities of using I4GL to communicate with any programming language while still enjoying the ease of coding using I4GL.

Resources

Learn

• "Deploy I4GL functions as Web services" (developerWorks, February 2009): Learn how Informix 4GL functions can be deployed as Web services. Get an overview of a user interface tool called "w4gl" and a back-end tool called "w4glc" that is in turn used by the "w4gl".
  
  
• 4GL Web Admin Guide: Link to an assortment of product manuals to familiarize yourself more with Informix 4GL.
  
  
• "New to SOA and Web services: Learn more about SOA and Web services.
  
  
• AXIS2/C: Find out more information about Apache AXIS2/C.
  
  
• Axis2 Quick Start Guide (The Apache Software Foundation, January 2007): Get started creating services and clients using Axis2.
  
  
• developerWorks Information Management zone: Learn more about Information Management. Find technical documentation, how-to articles, education, downloads, product information, and more.
  
  
• developerWorks Informix product page: Find articles and tutorials, and connect to other resources to expand your Informix skills.
  
  
• Stay current with developerWorks technical events and webcasts.
  
  

Get products and technologies

• Build your next development project with IBM trial software, available for download directly from developerWorks.
  
  

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About the authors

Gagan Maheshwari is a technical lead at IBM. He has worked on IDS and Informix 4GL (I4GL) as a design and development engineer.

Ramesh Srinivasan is a software engineer at IBM. He has worked as part of the Informix team as a developer for the past three years.

Navya Ramachandraiah is a software engineer at IBM. She is a member of the Informix 4GL (I4GL) development team.

Comments (Undergoing maintenance)

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Table of contents

• Introduction
• I4GL as a service consumer in an SOA environment
• Prerequisites
• Setting the environment
• Add a Web service
• Generate the configuration file and subscriber client code
• Call the Web service using an I4GL program
• Compile the sources to create an executable, and run the executable
• Conclusion
• Resources
• About the authors
• Comments

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