OverviewIncluded ConnectorsNaming ConventionsConnectorsConnector StateConnector PointsPoint CurPoint WritesPoint History SyncPoint ConversionsMultiple Connectors


The connector framework provides a standardized model for integrating to external systems. It is based upon the following key features:

  • Connector: a record which represents a connection to an external system or device
  • Connector Point: proxy point bound to a connector used to synchronize current value, writable value, or history
  • Tuning: a broad set of configuration options to fine tune connector behavior and performance
  • Learning: many connectors provide a mechanism to "walk" the external system for point-and-click UI tools
  • Diagnostics: the framework includes detailed debugging and network tracing tools
  • Axon API: a suite of Axon functions to access protocol specific functionality
  • Fantom API: a suite of Fantom APIs make it easy to create your own custom connectors

Included Connectors

Haxall provides a rich library of ready to use connectors:

  • Haystack: provides client connectivity via the Haystack HTTP API (used for Niagara)
  • MQTT: connects to a broker to publish and subscribe to topics
  • SQL: connect to relational databases using JDBC
  • Modbus: client support for TCP and RTU modbus protocols
  • oBIX: client and server support for oBIX XML protocol
  • Sedona: client support for the Sedona Sox protocol
  • Nest: connect to Google smart device management including Nest thermostats

SkySpark includes the following additional connectors:

  • BACnet: client support for BACnet IP
  • OPC: client support for OPC UA
  • EnergyStar: integration with Energy Star Portfolio Manager
  • SNMP: client support for SNMP typically used with IT equipment

Many third party connectors are also available on StackHub. Or you can build your own custom connector with the connector framework APIs.

Naming Conventions

The connector framework relies heavily on naming conventions to promote consistency. Everything is based on the library name. Let's look at the haystack connector as an example:

This same pattern is enforced by the connector framework across all connector types. If you know the library name, then you can infer all the other names.


Each connector instance is a record in the Folio database that models a logical connection to a remote system. A connector might model an external device, server, or database. Each connector has a unique address and communication protocol to integrate with the external entity.

The following tags are typically used to configure a connector:

  • fooConn: required marker tag for specific connector type
  • conn: required marker tag
  • uri: most connectors use this tag for the address of remote system
  • username: when authentication is required to remote system
  • password: when authentication is required, then password should be stored in password db by connector's record id
  • disabled: marker tag which disables the connector

The following transient status tags are managed by the framework itself:

  • connStatus: ok, down, fault or disabled
  • connState: close, opening, open, or closing
  • connErr: error message if connStatus indicates error condition
  • additional debugging details are available via the details

In addition to the tags above, each connector defines its own tags for meta data about the remote system/device. This data is queried from the remote system during ping and typically includes:

  • make and model of remote device or software
  • hardware/software version of remote system

Connector State

Every connector maintains an open/close state available via the connState tag:

  • closed: connector is closed
  • closing: connector is currently inside its onClose callback
  • open: connector is open
  • opening: connector is currently inside its onOpen callback

The framework manages the state, however the semantics of open will vary based on the connector type. For session based HTTP connectors open means that a session has been obtained to reuse between calls. For TCP connectors it means that a socket has been open to the remote system. For UDP protocols it might mean only that a ping request has been successful.

Separately every connector maintains a status via the connStatus tag:

  • ok: connectivity is normal
  • fault: configuration problem
  • down: communication or network problem
  • disabled: manual disable using the disabled tag
  • unknown: status not computed yet (boot state)

The status is managed by the framework; typically it is transitioned after the onOpen callback either succeeds or fails. Note that is common for the state to be both ok and closed - a connector is not kept open unless an application has a current need for it to be open.

Connector Points

Most connectors support synchronization of point data:

  • cur: subscription/polling of current, real-time value
  • writes: writing to an output
  • history sync: synchronization of time-series history data

Connector points are modeled as follows:

  • Must be adhere to standard point ontology
  • fooPoint: annotates the point as a specific connector type
  • fooConnRef: associates the point with a specific connector
  • fooCur: remote system address to synchronize real-time current value
  • fooWrite: remote system address used to write to an output
  • fooHis: remote system address to synchronize historical time-series data

Not every connector supports all three features, in which case only the applicable tags are used. Each of these point features is described in more detail below.

Point Cur

Points which support current value are modeled with the cur tag. Connectors can be used to automatically synchronize a point's current value using the curVal tag. Current value synchronize occurs one of two ways:

  1. Manual synchronization via the connSyncCur() function
  2. Automatically when the point is put into a watch

The mechanism for current value synchronization is specific to each connector type and protocol. However most connectors use one of the following strategies:

  • periodical polling of points in a watch - tunable by the pollTime configuration option
  • change-of-value (COV) subscription for protocols which support it

Connector points, which are using current value subscription will maintain their status via the curStatus tag:

  • ok: all is okay
  • stale: the point's curVal is not fresh data
  • fault: a configuration or hardware problem - see curErr
  • down: a communication or network problem - see curErr
  • disabled: manual disable of the point or connector
  • unknown: we don't know anything (boot state)
  • remoteFault: point in remote system is fault
  • remoteDown: point in remote system is down
  • remoteDisabled: point in remote system is disabled
  • remoteUnknown: point in remote system is unknown

If the parent connector is in an error/disable state, then all child points automically inherit the connector status.

The framework will automatically transition the status from "ok" to "stale" after 5min. This time can be tuned via the staleTime option.

Point Writes

Haystack models writable points with the writable marker tag. Writable points maintain an internal 16 level priority array by the point library. The effective value of the priority array is available via the writeVal and writeLevel transient tags. The effective level may be written to a remote system by connector. By default writes are issued whenever the local array's effective value is modified. However there are many tuning options to control write timing:

Connector points configured to write will maintain their status via the writeStatus tag:

  • ok: last write was successful
  • down: connectivity/networking problem - see writeErr
  • fault: configuration or hardware error - see writeErr
  • disabled: manual disable of the point or connector
  • unknown: we don't know anything (boot state)

If the parent connector is in an error/disable state, then all child points automically inherit the connector status.

Point History Sync

Some connectors support history data synchronization when the underlying protocol provides the respective feature. History syncs must be scheduled with the task library and the connSyncHis() function. After the initial history sync, then this function is scheduled using a null span to sync history items after the last sync.

Here is an example task that synchronizes all haystack history points every 1hr:

dis:"Sync Haystack Histories"
taskExpr: "readAll(haystackHis).connSyncHis(null)"

Connector points configured to sync history maintain their status via the hisStatus tag:

  • ok: last sync attempt was successful
  • fault: a configuration problem - see hisErr
  • down: a communication or network problem - see hisErr
  • disabled: manual disable of the point or parent connector
  • unknown: we don't know anything (boot state)
  • pending: sync has been scheduled and is waiting to running
  • syncing: not used by connector framework

If the parent connector is in an error/disable state, then all child points automically inherit the connector status.

For connectors which do not provide history synchronization, you can setup current value subscription and use local history collection

Point Conversions

The following tags are used to configure conversions between the normalized data stored in Folio and the connector's remote device:

  • curConvert: converts from raw read value to curVal
  • curCalibration: adjusts read value before updating curVal
  • writeConvert: converts local writeVal to raw value to write to remote system
  • hisConvert: converts history items read from remote system before storing locally

The conversion is specified as a string using the point convert syntax.

For example, if a connector provides temperature data in Celsius which we wish to convert to Fahrenheit, then we can add this tag to our point:

curConvert: "°C => °F"

If the sensor needs calibration, we might further decide to adjust plus or minus a few degrees. If for example we wanted to add 2°F to the value being read from the sensor then:

curConvert: "°C => °F"
curCalibration: 2°F

If we were also writing a value for the same point, then we would need to reverse the conversion for the write direction:

curConvert: "°C => °F"
curCalibration: 2°F
writeConvert: "°F => °C"

Use the details to debug the raw and converted values.

Multiple Connectors

Standard practice is to associate a given point to one connector. However, it is possible to assign a point to multiple connectors for different protocols. For example, a point can have both a bacnetConnRef and a sqlConnRef. When you configure a point this way, the default behavior is to log a warning:

Duplicate conn refs: bacnet + sql [@xyz]

If you truly wish to use multiple connectors, then you must apply the connDupPref tag with the connector name that should take precedence. This is the protocol that will be used by default for operations such as auto-subscription of watches and history syncs:

dis: "Dual Conn Point"
bacnetConnRef: @bacnet-conn
sqlConnRef: @sql-conn
connDupPref: "bacnet"

You can explicitly determine which connector is used for the connSyncCur() and connSyncHis() functions by using the connPointsVia() function.

Note: the system cannot update its lookup tables on the fly when adding/changing the connDupPref tag. You will need a restart for it to take effect.