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

56-10 Industrial Communication Systems
Parameter
1..*
Menue
1
1..*
Documentation
1
Plant
1
1..* 1..*
Machine
1
1..*
Catalog
1
External resource
role=“Catalog”
role=“HMI”
FIGURE 56.8
Mapping of a Web portal content description model to a (symbolic) XML file.
XML not only provides a method for defining the relations, but also for context-dependent filtering
and access. The content description should follow a model defining the specific requirements for
expressing the relations. These can be modeled as specific elements of the XML schema. Finally, in the
description files the relations are inserted [WOL03]. Figure 56.8 shows a fragment of the model and the
mapping toward XML.
56.4.2 Browser-Based Applications
Browser-based applications are typically used for visualization purposes. Respective solutions can be
found in nearly every visualization-related product in automation. The ability to cover large distances
makes such solutions especially interesting for all tasks that require remote access to the automation system,
for example, remote maintenance. Instead of requiring specific protocol installation, only TCP/IP and
the above mentioned transport-related protocols like HTTP are necessary, a Web browser on the client
is typically also available. This simplifies installation and maintenance efforts dramatically. However,
the browser alone is not always sufficient, since often complex, animated graphics have to be shown.
In addition, the information presented has to be enriched with dynamically changing data from the
process.
Several solutions are available to solve the problem sketched above. The data are provided by gateways
to the automation system’s components, by controllers, databases, or by using standard interfaces like OPC
[OPC98]. The transfer of the data can be done using HTTP or SNMP. The dynamic parts of the solutions
can be realized with client-side or server-side functions using technologies mentioned above. However, the
specific solution has to reflect the requirements adopted from the use cases. For example, a requirement
could be to allow access from clients with restricted capabilities in communication bandwidth and graphical
resolution of the display like mobile phones or handhelds. This requires personalization of the data to
be displayed. Another topic is the necessity for browser plug-ins. For example, displaying a flash animation
or SVG content requires the prior installation of the appropriate plug-ins. This limits the general applicability
of such a solution. Furthermore, an installation on-the-fly might not be always possible because of
access restrictions and insufficient user rights.
Another important topic is the protection of intellectual properties. If client-side scripting is used,
for example, JavaScript, the scripts need to be downloaded to the client’s browser. Since the functions are
executed within the browser’s scripting engine, they are transferred and thus are available at source
code level. So it is relatively easy to modify or to abuse them. A server-side solution, for example, using
© 2011 by Taylor and Francis Group, LLC