Historian Topic Syntax

Each historian will subscribe to the following message bus topics:

  • datalogger/*

  • anaylsis/*

  • record/*

  • devices/*

For each of these topics there is a different message syntax that must be adhered to in order for the correct interpretation of the data being specified.


The record topic is the most flexible of all of the topics. This topic allows any serializable message to be published to any topic under the root topic record/.


This topic is not recommended to plot, as the structure of the messages are not necessarily numeric

# Example messages that can be published

# Dictionary data
{'foo': 'world'}

# Numerical data

# Time data (note: not a `datetime` object)


The devices topic is meant to be data structured from a scraping of a Modbus or BACnet device. Currently drivers for both of these protocols write data to the message bus in the proper format. VOLTTRON drivers also publish an aggregation of points in an all topic.

Only the `all` topic messages are read and published to a historian.

Both the all topic and point topic have the same header information, but the message body for each is slightly different. For a complete working example of these messages please see examples.ExampleSubscriber.subscriber.subscriber_agent

The format of the header and message for device topics (i.e. messages published to topics with pattern “devices/*/all”) follows the following pattern:

# Header contains the data associated with the message.
    # python code to get this is
    # from datetime import datetime
    # from volttron.platform.messaging import headers as header_mod
    # from volttron.platform.agent import utils
    # now = utils.format_timestamp( datetime.utcnow())
    # {
    #     headers_mod.DATE: now,
    #     headers_mod.TIMESTAMP: now
    # }
    "Date": "2015-11-17 21:24:10.189393+00:00",
    "TimeStamp": "2015-11-17 21:24:10.189393+00:00"

# Message Format:

# Messages contains a two element list.  The first element contains a
# dictionary of all points under a specific parent.  While the second
# element contains a dictionary of meta data for each of the specified
# points.  For example devices/pnnl/building/OutsideAirTemperature and
# devices/pnnl/building/MixedAirTemperature ALL message would be created as:
    {"OutsideAirTemperature": 52.5, "MixedAirTemperature": 58.5},
       "OutsideAirTemperature": {'units': 'F', 'tz': 'UTC', 'type': 'float'},
       "MixedAirTemperature": {'units': 'F', 'tz': 'UTC', 'type': 'float'}

# Message contains a dictionary of all points under a specific parent
{"OutsideAirTemperature": 52.5, "MixedAirTemperature": 58.5}


Data sent to analysis/* topics is result of analysis done by applications. The format of data sent to analysis/* topics is similar to data sent to devices/*/all topics.


Messages published to datalogger/* will be assumed to be time point data that is composed of units and specific types with the assumption that they have the ability to be graphed easily.

{"MixedAirTemperature": {"Readings": ["2015-12-02T00:00:00",
                         "Units": "F",
                         "tz": "UTC",
                         "data_type": "float"}}

If no datetime value is specified as a part of the reading, current time is used. A Message can be published without any header. In the above message Readings and Units are mandatory.