What are the suggested best practices for EXP and TTL in DSEP?

[joffinjoy]

As per our understanding, exp or expiry is the time after which that particular data must be refreshed by fetching again from the source.

For example; if a BAP caches a catalog of 10 sessions, exp could be the timestamp at which the earliest session finishes or closes further entry. Because as soon as that one session is unavailable to be searched, the cached catalog is stale. Is this the idea of expiry in DSEP? A timestamp that has got a dependency on the data that is being cached.

On the other hand, is TTL just a directive for BAP that guarantees that the data can be cached for a particular duration? I am guessing, unlike exp, TTL wouldn't be dependent on the data which is being cached. But instead would be a fixed value from the BPP that is providing that particular catalog.

Please advice on the correctness of our understanding.