Is it possible to extend the relevance data with data from external sources? And how is it possible?
We collect data in other systems and I need the possibility to extend the relevance data of a profile.
Another question regarding the relevance module is if it is possible to identify a profile cross devices and cross browsers?
Yes it is possible to use external sources. You will need to develop a custom collector.
The relevance module does not by default track across browsers/devices. Visitors are identified by a cookie which is of course browser specific. There are strategies possible for identifying someone across browsers/devices. The easiest would be to have a login. You would still need to link the data together in some way (eg, set the visitor id to the same id). This also has implications for privacy and needs to be thought out carefully. But it can be tricky to identify someone as being the same unless they expose some identifiable information.
It is possible, but you have to implement many, including collector runtime (Collector, Scorer, etc), Characteristics plugin (java + Ext.js), Collector Plugin (for Alter-ego feature), etc.
However, EIRE addon [1] will help save huge amount of time and effort. I even wrote about this good news [2], too.
Since 12.5, you can customize the VisitorIdsGenerator [1], which is used for visitors or visit if the cookie is not found yet.
So, if you can implement #createVisitorId() to return the same unique string for a visitor somehow, regardless of devices, then it might be a good solution.
FYI, the default implementation in the product uses UUID.randomUUID().toString() for both #createVisitorId() and #createVisitId() by default.