1.7 LANSA Web Function Transaction Server
When executing applications over the Internet, the HyperText Transfer Protocol (HTTP) is used. HTTP does not support a persistent connection state. There is no concept of a user session. Each request is a new request, which is unrelated to any previous request. To overcome this limitation, LANSA for the Web provides a Transaction Server for Web Functions.
Note: The state management feature of the transaction server is only required if you have Web-enabled existing procedural applications which require session or state management. If you are developing applications specifically for the Web using WEBEVENT functions, this technology is not required.
The LANSA for the Web Transaction Server is used to maintain a persistent connection between the client devices and the Application/Data Server. The Transaction Server uniquely identifies each user and allocates a unique LANSA job for each user. Subsequent requests from users, which are known to the Transaction Server, are routed to the appropriate LANSA job which is active.
The Transaction Server maintains a connection state for each user and caters for unsynchronized page requests. An unsynchronized page request can happen as a result of the Back button supported in the browser paradigm. For example, the user can page back to previous functions and then request a page. This unsynchronized page request can be disallowed since the request is not the logical sequence expected by the active application on the Server. If an unsynchronized page request has been made, the user will be informed that the request is not valid and the current display page will be refreshed (shown) to the user.
LANSA allows you to write specialized Web Functions so that your typical Internet user can still use the Back button to navigate in your applications. This style of application is achieved by using the *WEBEVENT option in your function. For more details, refer to WEBEVENT Functions.
The Transaction Server shields the developer from the complexities of maintaining connection states and allows you to concentrate on application design and development. The Transaction Server also includes a Transaction Monitor, which is used to monitor the activities of the LANSA jobs in process. LANSA for the Web allows you to specify a system wide timeout period or to have customized timeout periods for each user who is allowed to access your application.
The Transaction Server also allows you to limit the number of concurrent users on the Server. This feature allows you to restrict the number of active jobs running on your Server, thus limiting the amount of resources used by your Web applications.
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