Key Expressions

A key expression (KE) is Zenoh's naming system for all resources — it replaces URLs, topics, and resource identifiers in a single unified grammar.

Syntax

Key expressions are forward-slash-separated paths, optionally containing wildcards.

Expression	Meaning
`sensors/room1/temperature`	Exact resource
`sensors/*/temperature`	All temperature sensors in any room (`*` = one segment)
`sensors/**/temperature`	All nested temperature resources (`**` = any number of segments)
`sensors/**`	Everything under `sensors/`
`**/temperature`	Any temperature resource anywhere in the namespace

Key Expression Language (KEL)

Key expressions support intersections and inclusion tests, enabling the router to determine at compile time which subscriptions match which publications:

use zenoh::key_expr::KeyExpr;
 
let pub_ke: KeyExpr = "sensors/room1/temperature".try_into().unwrap();
let sub_ke: KeyExpr = "sensors/**/temperature".try_into().unwrap();
 
assert!(sub_ke.intersects(&pub_ke)); // true

Best Practices

Use hierarchical namespaces: {domain}/{entity}/{attribute}
Keep segments meaningful: robot/42/pose over r42p
Use ** sparingly — broad wildcards require the router to fan out to more subscribers