How PLC, HMI, MES, b2mml, L1, L2, OPC architecture works?

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Hi,

Recently I have he studying regarding OPC and how to get data form OPC Server.

I am using Kepware OPC server for getting data.

I have connected to Kepware and .NET application and able to save data into Cassandra.

Now I have no idea how in real time OPC gets data. I mean I have big confusion in architecture(Only having little idea about it).

Here is my understanding of architecture:

Please look at image

My doubts are:

1. Will HMI receive data from PLC and create new data?
2.There are L1,L2 data right? My assumption is L2 data is coming form HMI and L1 from PLC. HMI uses L1 tags and using some mathematical models will give L2 tags data.Am I right?
3. What is the data type from MES(Manifacturing Execution System) to PLC?
4. What is the data type from MES to OPC? Is it b2mml?
5. Configure all tags and there opc address to receive data from what? HMI, PLC or MES. I mean in kepware we will give address by it should be PLC address or MES address?

NOTE: I have mentioned few above questions in image too just to see according to architecture.

It would be a great help for me if some one try to explain these questions that are bugging me.

With regards,
Nithin B.

What I have tried:

I have searched on google. Got a lot of info which confused me more. So extracted basic doubts I have and putting them here for help from community.