The XML Data Access (XML-DA) specification is primarily concerned with the real time acquisition and control of data within a process control environment via XML Web Services.
XML-DA servers are sources of data and could be a front end for a propriatory control systems, other DA servers or they could be directly connected to physical I/O points. Any I/O point that is exposed by a XML-DA server is called a XML-DA item.
XML-DA clients can directly read or write the XML-DA items or they can establish subscriptions that require the XML-DA server to maintain a cache of the item values and only return the values that have changed since the last time the XML-DA client polled the server. |
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