In most higher level system, the accuracy and exact calculation result that are provided with decimal mathematics are required (especially for financial and business based systems). OPC UA needs to support decimal.

Propose two additions: Decimal and DecimalString be added. The support for DecimalString would not require any changes to the stack since it is just an extension of string type. For clients and servers that understand the type, they can convert it to a native decimal data type. This conversion may result in losses of accuracy, but no conversion error would result. Support for a native Decimal format would result in an upgrade to the stacks. Decimal would be able to be transmitted in a native binary format, with no loss of accuracy or conversions required. It would be a sub-type of number (i.e. that it is a numeric value) which would allow the use of this abstract datatype with regard to decimals. Stacks would be required to restrict transmission of decimal information to/from older versions of the stacks, (protocolVersion would be used to provide this support). Clients that are communicating to servers that are older will not send a decimal type as a base decimal type, but instead will send it as a DecimalString, a server that is communicating with a client that does is of an older version will encode decimals as there string representation. If the protocolVersions indicates that both support decimal than the decimal shall be encoded as the required decimal format (32, 64 or 128).

See attached document for an additional description of the decimal format