Comparison

DataHub Web Server - Comparison of web technologies

Each of the display technologies supported by the DataHub web server has their own advantages and disadvantages, which makes them more or less applicable, depending on the requirements of the project you are working on. If you have any questions on which approach would be most suitable to your specific needs then please contact us by sending email to support@cogent.ca.

	ASP	Polling AJAX	Streaming AJAX	Java
Web browser support	Desktop: Yes Mobile: Yes.	Desktop: Yes Mobile: Yes.	Desktop: Yes Mobile: Yes.	Desktop: Yes Mobile: No.
Plug-in / Active X required	No.	No.	No.	Yes. Java plug-in required.
Update speeds	No updates. - Manual refresh required.	Fast updates.	Very fast updates.	Very fast updates.
System resource requirements CPU and memory	Very low.	High compared to Streaming AJAX and Java.	Low compared to Polling AJAX, similar to Java.	Low compared to Polling AJAX, similar to Streaming AJAX.
Bandwidth requirements Will depend on point count and update rate	Very low.	Relatively high.	Moderate to low.	Moderate to low.
Security Password / SSL protection	Yes.	Yes.	Yes.	Yes.
Firewall friendly	Yes.	Yes.	Yes.	No. Requires firewall configuration.
Licensing Licenses required in addition to the standard DataHub Node license	DataHub Web Server license.	DataHub Web Server license.	DataHub Web Server license + DataHub TCP Link license for each connection.	DataHub Web Server license + DataHub TCP Link license for each connection.
Programming requirements	Uses DataHub scripting language.	Uses JavaScript.	Uses JavaScript.	Uses simple HTML. Requires knowledge of Java to build custom applets.
Types of Application Common uses	Good for displaying static or slow moving data. Used for shift reports and statistics.	Good for displaying fast moving data and alarm conditions. Used in web monitoring and trouble shooting applications.	Excellent for displaying fast moving data. Used in remote monitoring and diagnostics systems.	Best choice for very high speed and large number of users. Used in stock trading and process control systems for monitoring and HMI displays.
Other features	These different web technologies can also be used together in the same web page. For example, we often use ASP code to dynamically create AJAX tables that display live a large number of data points. The APS code does the repetitive task of writing table entries for each point in a specific DataHub domain and the web browser interprets the resulting JavaScript and builds the AJAX display accordingly. You can also use ASP to access data from an ODBC database and display it as part of the web page along with the live data from the DataHub.

More about ASP

Most process data does not update very quickly, so ASP is suitable for a wide range of applications.
ASP will typically use very few system resources and bandwidth, so it is good for low speed connections.
ASP is the most efficient method for handling a large number of user connections.
ASP pages are generated by a script running in the DataHub. This means you can use the script to bring in data from other sources, such as from SQL databases. The web page can then display data from both live sources and database or text file archives.
Web pages that are generated by ASP scripts can usually be displayed on all desktop and mobile web browsers. This is because while the scripts themselves are written in Gamma (the DataHub script language), the web pages they generate are delivered as plain HTML.
In order to see new point values in an ASP page, you need to refresh the web page manually.

More about AJAX

AJAX automatically updates the web page whenever the data changes in the DataHub, no page refresh is required.
AJAX can handle high speed updates to a large number of users. However, system resources on the server will increase as the number of points, the number of users and the speed of the updates increases.
AJAX displays are created using JavaScript programming, which means they are popular with web developers who wish to control all aspects of how the data is displayed in the web page.
AJAX can be displayed using most modern desktop and mobile web browsers, but some mobile web browsers may not support one of both types of AJAX display. We have found the Opera Mobile web browser to be one of the best for displaying AJAX on mobile devices.
Polling AJAX and Streaming AJAX differ as follows:

Polling AJAX web pages make requests for new data to the DataHub on a polling cycle. This means there is usually a higher load on the CPU compared with Streaming AJAX, but in many cases the update speeds are comparable.
Streaming AJAX web pages are highly efficient at moving data, which means they use very little system resources and much less network bandwidth compared to Polling AJAX applications.

More about Java applets

Java applets are the best choice for displaying high speed data in complex web graphics like gauges, trends and progress bars.
Java displays can typically handle a large number data points, updating rapidly to a large number of users.
In most cases, Java web pages use far less system and network resources than AJAX pages.
Java pages are often used for displaying executive summary screens for management, or as an HMI to remote facilities.
We provide a wide range of Java applets that allow you to create sophisticated web pages with no programming required. Just use a simple HTML editor to configure the applet code and you can have a working web up and running in a few minutes.
Java pages can be displayed using most modern desktop browsers, but they do require the free Java plug-in to be installed first. The plug-in will download and install automatically if it is not already installed on your system.
We have found that Java is generally not supported on mobile web browsers.

Links to Documentation

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