Created question in FIWARE Q/A platform on 11-09-2015 at 10:09
Please, ANSWER this question AT https://stackoverflow.com/questions/32519080/subscriptions-request-forwarding

Question:
Subscriptions & request forwarding

Description:
I've got two questions regarding Orion subscriptions.

If we register entity with provider application url in Orion and create a subscription for it (e.g. sending updates every 15 minutes), what will happen if there is no data in Orion's local DB? Will it query data provider to fetch data from specified url and then return this a subscription update, or will it return nothing?
This is somewhat related to the first one. Is there an option to specify "max duration" of an attribute value in Orion's local DB (e.g. if an attribute is not updated in 1 hour, delete it's value)?
We have the following example in mind: A subscription is set up for an entity to send update every 15 minutes to our server. Updates from sensors to Orion should be done every 5 minutes. Now, if something is not working with the sensor and it stops sending updates, we will get the last value stored in Orion DB forever, unless there's the "max-duration" option for that attribute that deletes the value if it's not changed in specified time period.
When subscription update is triggered, in case that there's no value for that attribute in Orion's local DB, it should query the provider application for data (Q1).