Methods of Page Generation
The image is created on the server and the client
browser refreshes its display routinely, causing the display to update.
The Client requests the server for information to fill
in the partly created page which it then generates.
When the software first starts, it creates a standard html page which can
be viewed by any standard browser. This page includes a reference to an
image file which will be the actual display on the client screen.
The image file is then regenerated routinely in order that the client
will view a new image. The regeneration process only occurs when a
request is made by a client, so no unnecessary overhead is imposed.
Multiple clients accessing the same page are supported by a single
image, it is not necessary to repeat the process for each client in
turn.
This process is designed to be as efficient as possible in terms of
both the server and the network. No special software is required
to be installed or licensed on the client computer, the pages displayed
are standard, simple html, which include a single image.
User Interaction
Web pages normally require some ability to react to user
requests to allow navigation.
In order that the web displays mimic the operation of
the control room HMI display
pages, hyperlinks are created at page design time for any Saturn objects
or display areas. This can include the ability to navigate away from
the Web HMI pages to other sites as necessary.
Careful thought was given to what actions might be taken on
browser displays and it was decided to limit user interaction to display changes
only. No control actions are taken on browser screens; these need to be done on
the actual HMI display directly. This is to avoid the complex issues
associated with Security, reliability of remote access and control / design of
multiple user based systems.
Other Options
In most cases, the internal web server provides the best and easy
to use method for web-pages. However, a number of other options are
included:
