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Intenet of Things (IoT) integration.
The expected model for using IBM Streams to analyze events or data from thousands to millions of devices (Internet of Things) is that devices will be connected to a IoT scale message hub and Streams applications will subscribe to messages from the message hub to access the device events and to send commands.
A device sends device events to the message hub. A device event contains an event identifier and a payload specific to the identifier. Streams applications subscribe to device events and send device commands to the device typically based upon analytics of the device events and other data sources. A device command also has a command identifier and a payload specific to the identifier.
Use of the streaming topic based publish-subscribe model is recommended to allow analytic applications to be developed and deployed independent of the connectivity to message hub.
This is achieved by submitting the a single application that connects to the device hub wich then publishes stream topics containing the device events, commands and optionally status updates. In addition it subscribes to a stream topic containing commands to be sent to devices.
Analytic applications then use EventsSubscribe, CommandsSubscribe and StatusesSubscribe to subscribe to streams to be analyzed.
Analytic applications use CommandPublish to send device commands to individual devices.
Devices publish device events that an SPL application can subscribe to using EventsSubscribe. The default is to subscribe to all event identifiers from all device types and ids. The operator is parameterized to allow only subscribing to a specific event id (which is really the type of the event) and/or a specific device type.
The assumption is made that the format of the event is JSON and the resulting stream is of type DeviceEvent. The jsonString parameter contains the event payload in serialized JSON. The event payload is a JSON object using event format specification, so that the application event data is the value of the d key.
The application event data can be extracted into an SPL tuple using DeviceEventExtractData. This operator takes an input stream of type DeviceEvent and produces a stream of type DeviceEventTs augmented with a dataType tuple type specified by the application. Since the application event data might be specific to the type of the eventId or even the combination of typeId and eventId an application may need to use a Split operator between the DeviceEvents and multiple DeviceEventExtractData invocations. An example of its use is in the com.ibm.streamsx.iot.watson.quickstart::Quickstart application.
Device status events, such as connect or disconnect, are subscribed to using StatusesSubscribe which produce a stream of type DeviceStatus.
Devices can be sent commands, an SPL application can subscribe to commands being sent to devices using CommandsSubscribe. The default is to subscribe to all commands identifiers for all device types and ids. The operator is parameterized to allow only subscribing to a specific command id (which is really the type of the command) and/or a specific device type.
An SPL application can send a command to a specific device using CommandPublish with the input stream type of DeviceCmd. The jsonString attribute contains the application specific portion of the command represented as serialized JSON.
Applications can use CommandTupleToPayload to convert an SPL tuple representation of the command payload to JSON.