wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

56-8 Industrial Communication Systems
scripting of the elements. Browsers can use plug-ins for rendering and display. Other XML-based
formats are available for use in multimedia applications. They may be used in industrial applications
whenever they become standards and the support by tools is stable.
56.3.3 technologies for Server-Side and Client-Side Functions
The functionality of combining content description, application-depending interpretation, and transport
is provided at both the server side and at the client. Different technologies have been developed.
Popular client-based solutions are—without making any claim to be complete—JavaScript, Java-
Applets, ActiveX-Controls, and Flash. They require client-based runtime environments, like Java
Virtual Machine (JVM), Flash Players, and alike. They might be available bundled with the client software
(e.g., a browser), or may require installation of plug-ins. An interesting and rapidly used approach
is Asynchronous Javascript and XML (AJAX), which allows highly interactive applications with automatically,
dynamically loading and rendering of information fragments.
Well-known server-based technologies include PHP, Java-Servlets, Active Server Pages (ASP), and
Common Gateway Interface (CGI). In this case, the server component requires the runtime environment,
for example, scripting engines or servlet containers. The latter are often bundled with Web servers;
Apache Tomcat is an example.
Applications of client- and server-side technologies in the industrial domain can be compared to standard
IT-based solutions. They are as manifold as the technologies supported. Depending on the use cases,
a combination of different technologies may be required. Additional constraints may be derived concerning
real-time aspects, data consistency, and data and interface management. Typically, gateways to
underlying levels of the automation pyramid (see Chapter 13) are implemented at the server components.
An important feature for selection of a server- or client-side technology in the industrial application
area is its maturity, often treated as a combination of time of availability, standardization, tool support,
etc. Taking into account the typical life cycles of automation systems ranging from 3 to 5 years in factory
automation to more than 40 years in process automation and power plants, newly introduced technologies
are hesitantly applied.
56.4 application Examples
The application of Internet technologies in Industrial automation depends on the specific use cases.
These use cases also define the criteria for technology selection. Thus, the application range becomes
broader and broader. Without claiming completeness, some of the typical application examples are
described in this section.
56.4.1 Description Technologies
Device descriptions like Electronic Device Description (EDD) [IEC07] became more and more important
for many applications in industrial automation, especially in engineering and network set-up,
but not limited to. Together with the evolving functional complexity of field devices the description
languages had to be adapted in order to reflect all the features of devices. They typically require specific
parsers and interpreters for integration into applications. These parsers and interpreters have to
be adapted as well upon changes of the description language. It is quite usual that several parsers exist
within one application, allowing to support a broad range of field devices and different networks.
XML seems to solve several of the problems stated above. XML as a meta language is intended to
be used for the definition of specific languages—device descriptions are an example for this. Good
quality parsers and software tools are available and can be easily integrated into applications. So using
an XML-based device description would reduce implementation efforts at the application processing
device descriptions. Thus, several activities have been started to define XML-based device descriptions.
© 2011 by Taylor and Francis Group, LLC