Choosing a DataWindow technology
Since DataWindow technology can be used in different environments,
it may not be obvious what approach you should take to implementing
your data-enabled application. This section describes the DataWindow
technologies available for the three basic application architectures
described in Building Enterprise and Internet Applications
and
the requirements for each DataWindow solution.
The basic architectures are:
- Client/server A program running on a client workstation accesses a database
running on a server. The user interface and business logic reside together
on the client computer. - Distributed application The user interface on the client computer calls components
on a middle-tier server, which execute business logic and access
the database server. - Web application A client Web browser sends requests for HTML documents to
a Web server. The Web server passes control to an application server,
whose server-side scripts can access components and databases on
other servers.
Solutions for distributed and client/server
applications
Both the PowerBuilder DataWindow and the DataWindow, Java
Edition for PowerJ can be used in distributed and client/server
applications.
The one you choose depends on the development environment
and language you want to use.
PowerBuilder DataWindow
You can implement the PowerBuilder DataWindow as a control
that displays a DataWindow object or as a DataStore that supports
data retrieval and update without displaying the data. A complete
set of events and methods programmed in PowerScript provides control
over all aspects of the DataWindow, including data retrieval, display,
validation, and update.
For more information, see “PowerBuilder DataWindow
control”.
DataWindow, Java Edition
The DataWindow, Java Edition is a set of JavaBeans components
and associated classes for use in Java applications. It implements
all the features of the PowerBuilder DataWindow except rich text,
graphs, and OLE. Nearly all PowerBuilder events and methods are
also supported in the JavaBeans components.
For more information, see “DataWindow, Java Edition”.
Solutions for Web applications
You can use these DataWindow technologies in Web applications:
- Web DataWindow (and Web DataWindow DTC)
- DataWindow Web control for ActiveX
- DataWindow plugin
Web DataWindow
The Web DataWindow is a thin-client DataWindow implementation
for Web applications. It provides most of the data manipulation,
presentation, and scripting capabilities of the PowerBuilder DataWindow
without requiring any PowerBuilder DLLs on the client.
Functionality
The Web DataWindow supports a subset of the PowerBuilder DataWindow events
and methods, including dynamic modification of the DataWindow object.
The user can modify and update data. Graph, OLE, and RichText presentation
styles and controls are not supported.
Client requirements
The technology works in any browser, but the appearance of
the generated HTML is usually best in Internet Explorer. Generated
HTML can be dynamically optimized for Netscape or Internet Explorer
or scaled back to handle older browsers.
Server requirements
A component server and a dynamic page server work together
to generate a client control with data and include it in a Web page.
Each time the user requests a new page of data, updates data, or
inserts or deletes rows, the server gets a request to generate a
new page. Depending on how state is managed, the component may retrieve
data each time it is called, causing added load on the server.
Development tools
The Web Target interface in PowerBuilder provides the Web DataWindow DTC that
you can use to develop Web DataWindows without hand coding. You can
also write your own server-side scripts to create Web DataWindows
using the component server’s API. You can write the scripts
for interpretation by a specific page server type (PowerDynamo or
Active Server Pages), or you can use the Web Target object model
to write server scripts that are type-neutral (can be deployed to
either PowerDynamo or Active Server Pages).
When you use the Web DataWindow DTC on a 4GL Web page, server-side events
are available and page variables can enhance the dynamic capabilities of
your Web application.
For information about the Web DataWindow, see Chapter 6, “Using the Web DataWindow” For information
about the Web DataWindow DTC, see Working with Web Targets
.
DataWindow Web control for ActiveX
The DataWindow Web control for ActiveX is an interactive DataWindow control
for use with Internet Explorer that implements all features of the PowerBuilder
DataWindow except rich text.
Functionality
The Web ActiveX is fully programmable and supports DataWindow
events, methods, and dynamic modification of the DataWindow object.
The user can modify and update data. The RichText presentation style
is not supported.
Client requirements
The control uses ActiveX technology and works in Microsoft
Internet Explorer only.
The user must download the CAB file for the component, which
is a little more than one megabyte in size. Database connection
via JDBC occurs from the client, which must be configured with the
connection software. The software can be downloaded from the Web
server.
DataWindow behavior that would compromise security of the
client, such as SaveAs, is disabled.
Server requirements
The JDBC database connection can access databases on a remote
server.
Development tools
You can use the Web Target tools for working with ActiveX
components to develop your Web application.
For information, see Chapter 8, “Using the DataWindow Web Control
for ActiveX”
DataWindow plugin
The DataWindow plugin is a browser plugin that displays Powersoft
reports (PSRs).
Functionality
A PSR is a frozen
DataWindow; it cannot
be modified and the data does not stay current. However, a PSR is
a compact representation of the DataWindow definition and data and
can be downloaded efficiently. It is an efficient means of viewing
batch-produced reports.
The user cannot modify or update the data.
Client requirements
The plugin executable must be installed in the browser plugin
directory. It cannot be downloaded and installed automatically.
The plugin works in both Netscape and Microsoft browsers. DataWindow
behavior that would compromise security of the client, such as SaveAs,
is not
disabled.
Server requirements
None.
Development tools
You can use InfoMaker, DataWindow Builder, or PowerBuilder
to create PSRs. You can develop Web pages that include reports in
PowerBuilder or PowerJ.
For more information about the plugin architecture, see Application Techniques
.