Working with Metadata

Device metadata represents definitions of variables (settings), functions (operations) and events (notifications) provided by a device. Flexible driver supports two types of device metadata:

• Static metadata assumes that definitions of available variables/functions/events are fixed in server-side device profile
• Dynamic metadata assumes that variable/function/event definitions are retrieved from the device during synchnonization

Configuration of flexible driver differs in static and dynamic metadata cases.

Configuring flexible driver to use fixed sets of variables/functions/events is relatively easy. It's necessary to fill Static Variables, Static Functions and Static Events tables described in Device Account Properties section. Those tables define parameters and formats of device entities, as well as variable reading/writing and function execution rules.

To configure flexible driver for reading definitions of variables/functions/events from the device, do the following:

• Set up Variable Definitions Expression, Function Definitions Expression and Event Definitions Expression in Dynamic Metadata group of Operations section in device profile. Each of those expressions should return a Data Table representing a list of all variables/functions/events retrieved from the device. Each row in those tables must contain definition of one variable/function/event.
• Tables returned by the above expressions will be processed row by row. For every row, driver will evaluate expressions from Dynamic Variables, Dynamic Functions and Dynamic Events group respectively. Once all expressions are evaluated, driver will use their results to construct a variable/function/event definition and add it to the metadata.

For every row of variable definitions table, driver will evaluate all expressions in Dynamic Variables group: Name Expression must return variable name Description Expression must return human-readable description of the variable Readable Expression must return TRUE if variable is readable and FALSE otherwise Writable Expression must return TRUE if variable is writable and FALSE otherwise Format Expression must return variable's format encoded as a string Group Expression should return variable's group or NULL if doesn't belong to any group Help Expression should return detailed description of the variable Read Request Expression should return text of another expression that will be used to prepare variable reading request that will be sent to the device Read Request Parsing Expression should return text of another expression that will be used to convert device reply to new variable's value Write Request Expression should return text of another expression that will be used to prepare variable writing request that will be sent to the device Write Request Parsing Expression should return text of another expression that will be used to check whether write operation was successful

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