OPC UA File Transfer concepts

The OPC UA File Transfer is a set of functionality in OPC UA, built on top of core OPC UA, which defines operation on files and directories residing in the OPC UA server that supports it, similar to file system functionality in operating systems. The OPC UA files and directories can be just a temporarily or persistent storage for arbitrary data, with no added intrinsic semantics, but in many cases they will have a specific meaning defined by the OPC server. For example, files with a predefined name and location can be used to upload a new firmware to the PLC. Files provided by the OPC UA server can also be "virtual", i.e. they do not have to be physically stored inside the server, and the file transfer mechanism can be used to facilitate access to large bodies data that would otherwise be impossible to read or write in a single call (files can be read from or written to in pieces). Some OPC UA "higher-level" specifications use the File Transfer mechanism as well. For example, files are used in Certificate Management to transfer application certificates in their binary form.

Note: The "file transfer" in the name corresponds to how the related OPC UA specification part is titled. In reality, the functionality covers more than just file transfer - it represents a file system in OPC UA, and provides file access and manipulation operations.