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Article - May 2000
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XML: Esperanto for Data 
Richard Desmarais
 VP Engineering

XML ( Extensible Markup Language ) is emerging as the standard language for data exchange in many businesses sectors, including building automation.

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Teletrol Systems Inc.


In the building automation industry today, standard protocols such as BACnet are available for exchanging data across the wire but do not address many of the other boundaries that exist between building automation systems from different manufacturers. Microsoft and many of the technology companies involved in data exchange over the Internet have recently made a meta-language called XML their Esperanto. XML (extensible Markup Language) is emerging as the standard language for data exchange in many business sectors, including building automation. Manufacturers that adopt XML with standard schemas for storing and retrieving configuration information give their customers the option to configure their controllers and store that information using a variety of custom and third party tools.

Reliable Controls XML is a derivative of SGML, the Standard Generalized Markup Language, which is a standard, vendor-independent and platform-independent language way to represent and store data. HTML, the language used to create the web pages that you see in your browser, is also a language that was originally created as a part of SGML. While HTML is well suited to displaying information, it does not provide the structure necessary to organize and exchange data. XML allows data to be stored in a human readable file format that can be viewed using a web browser or even a word processor. Other tools available on the market, and many free or shareware applications, allow XML to be viewed and edited in a hierarchical way, much like Microsoft Explorer allows the files and directories on your hard drive to be viewed in an intuitive "tree" structure. The reason the data can be represented in this familiar way is that XML uses tags, much like HTML data tags, to record the relationships between the data elements. When an XML data file is read, it's easy to see that the device is called 'Controller' and it contains objects such as points, messages, and alarms. Using HTML, it would be impossible to represent that points, messages, and alarms are part of the Controller, but instead the data would appear to be a simple list.

Here is an example of what's contained in an XML file that might be used to configure a controller:

    <Controller> 
   
         <Point1>
                <name>Outside Air Temperature</name>
                 <conversion-formula>Degrees F</conversion-formula> 
                <location>Near Door 7</location>
            </Point1>
   
         <Point2>
                <name>Space Temperature</name> 
                <conversion-formula>Degrees F</conversion-formula> 
                <location>NE Quadrant</location>
            </Point2>
    </Controller>

Although XML allows data to be represented, stored and recalled, it does not address the issue of what kinds of data should be used to represent a particular physical or software object. To solve this problem, the XML community had adopted the idea of a schema. A schema is simply a definition that says if you wish to represent something called a "Point" object, to use the previous XML example, it should contain the properties called name, conversion-formula, and location. While XML is the language that allows the data exchange, the schema is the agreement as to what types of data will be necessary as part of the exchange. The BizTalk consortium has facilitated the development of standard schemas for many industries with the support of Microsoft. Without the development of these common definitions as to how to represent the price and quantity of goods to be sold electronically the emerging e-commerce revolution would not have been possible.

By supporting XML and standard schemas for building automation objects, manufacturers give their customers the flexibility to use their configuration package, a package from another manufacturer, or a third party software package that supports XML as a file format such as Microsoft Excel or Access. Because Microsoft is now freely distributing its XML software engine, it's much easier to create custom applications to read and write XML data, possibly even reading proprietary configuration data files and exporting them to standard XML schemas.

Conclusion

 XML and schemas have emerged as powerful technologies in the push to achieve vendor and platform independence in the building automation industry. This independence has accounted for their rapid acceptance and deployment in other industries. Currently, XML can provide these advantages in building automation system configuration; in the future, it may allow building automation systems to seamlessly communicate with other non-physical systems such as accounting and scheduling packages. It stands as a technology of choice for vendors interested in interoperability and standards.

Teletrol Systems Inc., located in Manchester, NH, is the manufacturer of the new, Web based, BACnet compliant eBuilding system. 


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