Message types

Open Message Format (OMF) message types have the following categories:

• type

• container

• data

Each message type creates a different type of data within the PI System and contains keywords that define characteristics of the data. Most of the message types are used to create the structure of the data and give it meaning. Dynamic data messages contain time-series data for which the PI System is known. The message types, their keywords, and the data they create are described in detail in this section.

The OMF application should send each message only once. Types, containers, static data, and links should be sent when the OMF application is started for the first time to create the structure of the data. Under normal circumstances, the OMF application should not re-transmit this information every time it is restarted. PI Web API stores the necessary information in its cache to successfully receive data values. The OMF application should send new dynamic data messages as the data is created, because dynamic data messages create the stream of data into Data Archive. To prevent duplicate data, each unique dynamic data message should only be sent once.

OMF Actions

PI Web API supports a subset of OMF actions that define how objects and data are created, modified, or removed. Supported actions include the following:

• CREATE action

  This is used to create new objects and write new data in the PI System through PI Web API. It is supported for type, container, and data messages and is typically used to establish data structure (Types and Containers) and to send time-series values.

• UPDATE action

  This is used to modify supported properties of existing objects or to control write behavior for existing data, with availability and constraints that vary by message type and may include PI Web API-specific restrictions. It is not implemented for type messages.

• DELETE action

  This is used to remove existing objects created by OMF messages, with behavior varying by message type and, in the case of Containers, resulting in the permanent deletion of all associated PI Points.