TagNames Parameter
By default, the Historian REST service provides support to read samples for multiple tags. Multiple tag names are separated by semicolons (;). For example, "tagname1;tagname2;tagname3".
https://<historianservername>:8443/historian-rest-api
/v1/datapoints/currentvalue?tagNames=tagName1;tagname2;tagname3
Encode the semicolon as %3B
if using the URI format, as the semicolon is also a valid character for a Historian name, and the web service parses the tag names incorrectly if a tag name contains a semicolon.