Table 1 Pre-implemented operators for structured data (partial.)

The “Time Series Database” operator is used to observe certain data tables in a specified time series database (such as InfluxDB). When new data is inserted into the table, the operator will be able to obtain the data immediately and output it in a specific format to subsequent operators.

The “Device Input” operator provides real-time data access to a specified connected device on the Edge Node. The product type of the device should be specified in the operator, which determines the format of the data.

The “Filter” operator is used to filter the input data stream. The operator sets a conditional expression. Only when the expression is true, the corresponding data will be forwarded to subsequent operators, otherwise, it will be discarded.

The “Sample” operator samples the input data stream according to a specific step size as well as a time interval. The operator can reduce the processing frequency of real-time data and thus optimize resource usage.

The “Time Window” operator provides the function of batch forwarding the data arriving in a specified period.

The “Change Trigger” operator monitors its input and only generates outputs when data changes occur. This operator is suitable for data streams that have frequent data duplication in a period.

The “Aggregate” operator provides a variety of methods for aggregate computation on a data stream, such as sum, count, mean, mode, etc., which can complete some common statistical tasks.

The “Custom Function” operator provides the ability to calculate data streams with user-defined functions. The operator supports multiple custom computational expressions for each piece of data flowing through the operator and merges the results of the computation into the final output data stream.

The “Apply Model” operator calls a certain AI model to make inferences upon its input, and outputs the inferencing results. Note that the model to be called should have been already deployed on the Edge Node.

The “Device Output” operator provides the function of controlling devices, including setting the properties and calling the services of certain devices.

The “Notification” operator provides a logging-like function that persists input data as messages on the Edge Nodes. These messages can be set to different levels, including INFO, WARN, and ERROR. The notification messages can be used as inputs for some operators.