Working in an integrated Web delivery environment

In Web delivery environments, application and transaction
servers play a vital role in delivering dynamic content to Web site
users by extending the capabilities of a Web server and integrating
database management systems (DBMS) into the delivery strategy.

An application server processes server scripts to produce
customized pages, while a transaction server manages components
that encapsulate business logic and manage database connections.
An application server can integrate with, but does not require,
a transaction server.

Server types

Web delivery environments
use several types of application and transaction servers:

This type of server	Performs these actions
Application server as a Web server; personal Web server	Manages requests for Web pages
Application server as a dynamic page server	Processes server-side scripts
Component transaction server	Provides access to components that provide business logic
Database management system	Provides database access

These servers can run on one machine, or run on a number of
machines for load balancing.The following illustration shows an
environment where the Web server and application server run on the
same system, and the component transaction server on another system.
In this example, the application server uses its own database to
store all of the files included in the Web site:

Web servers and application servers

You can use any commercially available Web server that can
communicate with either of the following application servers:

Application server	Web server
PowerDynamo	PowerDynamo Personal Web Server or a third-party Web server that can communicate with the PowerDynamo application server through ISAPI, NSAPI, CGI or WIN-CGI
Active Server Pages	Microsoft Internet Information Server (IIS) or a Web server that can communicate with the Active Server Pages application server through ISAPI or CGI

These servers create dynamic pages on the fly by processing
server-side scripts. These scripts are part of a template (source)
page. A template page can contain HTML and client scripts as well
as server scripts.

An application server also acts as an intermediary between
a Web server and a DBMS. Page templates can be stored in one database
and the data accessed from Web pages in the same or in another database.
This is an example of how an application server (without a transaction
server) integrates into a Web delivery environment:

Transaction server

Transaction servers are used in multitier applications to
host executable components. They make it possible to shift processing
to the middle tier, enabling application clients, such as Web pages,
to remain thin. They can also handle the database connections, thereby
distributing the processing load and making it easy to manage the
connections via connection caching and pooling.

The EAServer component transaction server can host various
kinds of components, including Java classes, JavaBeans, Enterprise
JavaBeans (EJBs) and PowerBuilder objects. Web targets provide ready
access to a server and its components, including Web DataWindow
server components.

DBMS

A key feature of dynamic Web pages is the ability to retrieve
and update database information. A Web target’s support
for application server technologies makes it easy to incorporate
dynamic database content into Web pages. Adding a Web DataWindow
facilitates retrieving and updating database information for a Web
page.

Enterprise Application Server environment

EAServer provides the following services:

• Dynamic
  page server and personal Web server (PowerDynamo)
• Component transaction server (Jaguar)

The basic architecture and communications protocols used by
the transaction server and the page and personal servers are shown
below:

4GL Web pages provide enhanced integration with Enterprise Application Server environments. They
make it easy for you to access EAServer components, bind properties
of those components to controls on your page, manage page data,
and simplify server scripting tasks. However, you cannot use 4GL
Web pages if you deploy your Web pages to an application server
other than PowerDynamo, or if you use a transaction server other
than EAServer.

For how to work with 4GL Web pages, see Chapter 8, “Developing 4GL Web Pages”

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