Resources in PI Web API are addressed by WebIDs, which are persistent, URL-safe identifiers that encode the GUIDs and/or paths associated with objects in the PI System. WebIDs are often used in links, and can also be found inside JSON responses. Client applications can then use these WebIDs as opaque identifiers in other URLs or query parameters. Because WebIDs are persistent, clients may cache URLs containing WebIDs for future use, even in newer versions of PI Web API.
WebID version 2.0, introduced in PI Web API 2017 R2, provides different types of WebIDs (see: WebID Type). Specifying the WebID type gives you options for reducing WebID sizes (for URL length limitations), for identifying ambiguous paths/names of AF Event Frames and AF Notifications, and for accommodating path and name changes. Any existing WebIDs (from version 1.0) can still be used with newer versions.