BCS Question (scenarios when data source is unreachable)

Question

I have a few real-world (hopefully simple) BCS questions for on-premise database and SharePoint Online (O365) connected by OData web service:

In the scenario where the data source is unavailable/unreachable from the cloud:

(1) What does a user actually see if they try to access an external list in SharePoint while the data source is unreachable?

(2) What does a user actually see for an external data column in a document library (both for a new document and an existing document that had already been tagged with a database value)?

(3) When tagging a document with a database value, is the data actually cached in SharePoint (BDC) or does it strictly live inside of the properties of that document, or is it called every time a user views the properties of that document?

(4) If the data is changed (when SharePoint cannot reach it), what happens to a document that was already tagged with a database value (e.g. a customer name changes from "Customer1" to "Customer2"). Does it automatically update as soon as connectivity is re-established, or is there a synchronization concern I should be aware of.

Thanks in advance!

Answer 1

(1) SP will display it as it could not connect to the external data source. Sometimes we setup manual caching mechanisms and as I know, it supports caching by default for Outlook.

(2), (3) and (4) When a Business Data column is created, it creates another column associated with it which will be named with a suffix "_ID" to the Business Data Column. You can reload/ synchronize the data column if needed or just let it be there as it is. There is a refresh button with the column value.