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Data Types and Encoding

XML elements, containing one of the ESD encodings STRING, TIME and SCALARBIN may be mapped to XML Schema compliant data types and may therefore be validated by an XML parser. For instance, SCALARBIN encoded data could be embedded in an XML element like <value xsi:type="xsd:float">12.2</value>.

The only exception is the BINHEX encoding, which is fieldbus specific and may not be validated in detail. However, the format of the data may be checked by mapping the BINHEX type to the XML Schema ``hexBinary'' data type, which is basically the same99.

As shown above, the IGUANA gateway implements only a very limited set of data types. Underlying fieldbus systems may provide various other data types, such as specific date/time types, or complex types, like arrays or structures. Theoretically, it would be possible to map many of these data types to corresponding XML Schema types, hence implement some kind of data type translation. ESD provides the ``DPINFO'' command, which returns the fieldbus specific data type of a datapoint. This information could be used to represent the fieldbus data with a suitable XML Schema data type. However, the underlying data type is fieldbus specific, moreover, DPINFO will not return the data type for various fieldbus systems that simply do not provide data types. Hence, data type translation will be complicated to implement and may raise interoperability issues, therefore it is preferable to use the limited set of data types provide by the IGUANA gateway and and encode fieldbus specific data with the BINHEX data type.


next up previous contents
Next: Representing the IGUANA Interface Up: Encapsulating the IGUANA Protocol Previous: Addressing Scheme   Contents
Hermann Himmelbauer 2006-09-27