Tag properties (tag metadata)

Every AVEVA Historian tag is associated with one or more tag metadata instances. A tag metadata instance is a set of properties identified by a unique TagId. The TagId is a 16-byte globally unique identifier (GUID). Tag metadata properties include tag name, description, tag type, storage type, creation time, and so on.

Tag metadata properties describe what the tag is, where the data for that tag is coming from, how the timestamped data values(VTQs) of that tag should be stored, and how they should be retrieved and displayed by client applications. The following table describes the most important tag metadata properties:

Depending on values of these properties, additional properties provide more specific details. For example if a tag is an analog tag—that is, it represents a variable measuring a continuous physical quantity such as the temperature of a boiler—the tag metadata property RawType specifies what kind of numeric type is used, either float or integer. If it is an integer, the IntegerSize property specifies the number of bits in that integer, and so on.

Note: The ability to set up an alternate file storage location for tag metadata is possible to ensure it is available should the primary location become corrupt or not accessible.

For the full list of tag metadata properties, see the tag-related tables in the Tables chapter in the AVEVA Historian Database Reference.