Observer node implementation

Question

I have read corda observer node implementation here. as per documentation flow sends transaction to observer nodes to record in vault_states of observer node.

I have few questions related to observer nodes

1. Observer node can not be Participant and Observer at same time in any corda version. As per documentation needs to create 2 diffrent nodes for same. Can we make notary as Observer ?

2. Can we create one observer nodes between diffrent cordapp project? How observer node track which transaction belongs to which cordapp project?

3. In most of example observed build.gradle where observer node is same as party nodes. Is there any other attributes for observer node as corda notary have "notary" attribute?

Answer 1

1. If you are a participant, you still always store the state, so you don't need to also be an observer (the only exception is OwnableStates, where you store the state if you are the owner). The notary can be an observer

2. A node can store and/or observe transactions from any number of CorDapps. Transactions don't belong to CorDapps. One transaction could use classes from many different CorDapps

3. Unlike being a notary, being an observer isn't a role in the network. It's just something that a node can choose to do on a per-transaction basis