Terminology: 'Catalog' vs. 'Metadata Broker'

[sebbader]

We are currently speaking a lot about catalogs but - in my impression - think about a catalog hosting service. Which at the moment is the role of the IDS Metadata Broker.
To further increase the confusion, the IDS Metadata Broker's data model knows a connector catalog as well as a resource catalog. So let's find a few answers to make the discussion more efficient:

1. When we speak about a 'catalog', do we actually mean 'Metadata Broker'?
   1a) If yes, let's not use 'catalog' without the context of connector catalog or resource catalog any longer, especially when talking about the impact of DCAT for the IDS.
   1b) If not, what is our definition and in particular its relation to the 'Metadata Broker'?

2. If a 'catalog' is not an infrastructure service but can be operated by any connector for itself, do we still need to define the operations on it? Or isn't this implementation-specific?

3. Is a catalog IDS-specific, meaning can a catalog only contain IDS defined entities?
   3a) If yes, see 1a, do we still need to discuss it or isn't everything already specified?
   3b) If no, like for a pure cat:Catalog, how do we know how to interact with arbitrary catalog entries?