Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

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9.3.3 Data Integrity The Web was originally designed to enable you to retrieve and view documents available on the Web. In a read-only environment, you do not have to be concerned about recovery from failures when updating data. Consequently, Web servers do not provide facilities related to the integrity of data (HTML documents) that they access. OLTP systems, in contrast, take responsibility for the physical and logical integrity of the data they manage, using facilities such as logging, transaction backout, and deadlock detection, either directly or in cooperation with a database management system. OLTP systems can provide end-to-end recovery, ensuring that the user′s terminal has successfully received and displayed the transaction response before database updates are committed. Web-based applications typically end before the Web server attempts to send a response to the Web browser. They have no way of telling whether the response arrived successfully or not. For 3270 sessions, CICS provides recovery facilities that enable you to ensure that no data sent to or received from a 3270 terminal is lost. CICS decides when to commit changes to its resources. CICS clients using the ECI can manage their own data integrity by using the ECI_EXTENDED or ECI_NO_EXTEND parameters to control the scope of the LUW. See CICS Family: Client/Server Programming, SC33-1435-00, for more details. The Web cannot provide the same level of data integrity between the Web server and Web browser .So with a Web application you have at least two connections to consider: • The link between your Web browser and your Web server • The link between your Web server and CICS server 9.3.3.1 Data Integrity between Web Browser and Web Server If your Web browser and Web server are connected across the Internet, data transmission between them is not guaranteed. If your Web browser issues a request and receives a response indicating that the function completed successfully, you can be confident that the CICS transaction performed the function that you requested. If your Web browser does not receive a response, there is no way of knowing whether a CICS function that you requested was completed normally: • It may not have run. 138 CICS for AIX as the Transaction Server • It may have started and been completed normally, but the connection to the Web browser was lost before the results could be returned. • It may have been abended. • It may have been started and completed, but with the wrong result. Although you will not normally be maintaining data resources on your Web browser, you can still design the CICS and Web server components of your application to ensure data integrity and consistency.
9.3.3.2 Data Integrity between the Web Server and CICS Server The data integrity issues for the connection between the Web server and CICS server are no different from those for any other distributed CICS application. For example, you can use the ECI to manage an LUW that can span several calls to a CICS server program. 9.3.4 Processing State Information In a transaction processing environment, a business function can consist of several related transactions that you perform in a particular logical sequence. The application therefore needs knowledge of the current state of processing within the logical business function that is being performed. It also must be able to distinguish between different users performing the same tasks at the same time. When you use a Web browser, each time you select a new hypertext link, you might be accessing a different Web server. The Web server itself is stateless; it treats each request separately and independently and has no concept that a series of user interactions with the system can be related and make up a larger logical function. If you need to maintain information about the state of processing in an application using the Web, you must maintain information about the state of processing either with the Web browser or on the Web server, using programming interfaces such as the CGI. OLTP systems understand state and provide facilities to help you keep track of state within your applications. CICS, for example, allows one transaction to specify which transaction is to process the next input transaction from a user. It also provides facilities such as the CICS COMMAREA and temporary storage queues that enable you to easily maintain state information and pass it from transaction to transaction. 9.3.4.1 Saving Processing State Information You may want a mechanism that enables you to save processing state information that can be retrieved when new input is received for an ongoing Web conversation. You first have to decide where you want to manage your information about the state of processing: on your Web server CGI script or the CICS server. Web Server State Information: One method of minimizing the amount of information about the state of processing that has to flow across the network is to keep the information about the state of processing in storage on the Web server and allocate a unique identifier to that information. You can then send the unique identifier in the form, so that when the forms input is received, the Web server can use the unique identifier to retrieve the information about the state of processing for that conversation. You may decide to do some or all of your state management on the Web server. One of the advantages of doing at least some of the state handling on your Web server is that it can perform a routing function. If you have multiple CICS servers, you can put code into your CGI script to analyze information about the state of processing returned by the Web browser and invoke the appropriate CICS server for the requested function. Thus your Web server can provide a routing function similar to that provided by a CICS TOR for conventional CICS transactions. Chapter 9. Accessing CICS from the Web 139
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Addressing OLTP Solutions with CICS
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1.2 Complex OLTP Business Environme
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Figure 2. OLTP Complex for XYZ Insu
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1.5 OLTP Market 10 CICS for AIX as
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Figure 5. OLTP Market Segmentation
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2.1 IBM Software Servers 2.1.1 Lotu
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2.2.1 CICS Clients V1.1.0 A Transac
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2.2.4 CICS Internet Gateway for AIX
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3.1 Services CICS for AIX is a very
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3.1.2 CICS API 24 CICS for AIX as t
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3.2 Implementation 3.2.1 Components
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3.2.2 Processes 3.2.1.3 Application
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3.3.1 DCE RPC 3.3.2 TCP/IP 32 CICS
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Figure 9. Interconnection Using Enc
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connect to a PPC Gateway server mac
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Figure 12. Interconnection Using TC
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3.4.3 Configuration 3.4.4 Managing
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3.4.6 Intersystem Communication CIC
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3.4.8 Data Location 44 CICS for AIX
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3.4.11 Operations plan to cope with
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3.5 Summary 48 CICS for AIX as the
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Figure 13. Application Server Model
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4.2.1 CICS External Call Interface
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4.5.2 CICS Client for DOS 62 CICS f
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4.5.5 CICS Client for AIX CICS Clie
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