ExportMarker (Json Export Marker)

Provides a way to mark a component for data export to JSON. You use this method rather than binding to an ord, bql, neql, or an absolute path.

The toolkit provides three ways to select control point data for export:

Add an absolute ord binding to a JSON schema.
Use bql or neql to identify control points to a relative JSON schema.
Add a JsonExportMarker to a component.

Marking a component offers several benefits beyond just marking points to include in a RelativeJsonSchema. For example, markers support the export of alarm and history data for specific points. Markers can store a unique identifier supplied by a third party platform. This can be used to differentiate between registeredpoints with an ID and unregistered points without an ID. For example, with markers JSON can send different payloads prior to registration including more detailed information (units, min/max, descriptive tags) than should be sent upon every change of value.

When applied to a numeric point, a JSON export marker introduces a CovTolerance property to reduce unwanted updates from the station if a value changes only slightly. You may also use the export marker with incoming JSON payloads.

Figure 68. ExportMarker properties

To use this marker, expand the ExportMarker node in the palette and drag an ExportMarker to a point in the station.

Property	Value	Description
Id (ExportMarker)		Provides an id from the cloud platform. The expectation is that this value will be unique, at least within each station as it may be used by the cloud platform as a primary key.
Platform Writable (ExportMarker)	`true` or `false` (default)	Used with the setpoint/override feature to prevent writes from the upstream platform.
filterEnabled	`true` (default) or `false`	Turns the filter on and off. When disabled, the schema ignores `CovTolerance`.
CovTolerance	number to two decimal places	Sets up an amount that defines a range of values within which a given value may vary without requiring the station to update the value. This eliminates the overhead required to update when a value changes only slightly.
lastPublishedValue	read-only	Reports the most recent value that was exported.

Examples

Example	JSON
Base query	`station:\|slot:/\|bql:select * from jsonToolkit:JsonExportMarker`
BoundProperty binding ord	`slot:..` (References the parent of the JsonMarker Base)