wilsonmax wrote:So, one thing can be sure is that:
A connector from IBM, ERP vendor or external-partner is required when importing data from any ERP (when there is no staging DB) since the existing interface and function cannot cater it, right?
Wrong.
I'm not sure where you get this idea. Almost every single ERP system out there uses either an Oracle or SQLServer RDBMS as its database backend. Connecting to the ERP system is usually no more than installing the appropriate ODBC driver and being provided with a username/pwd by the DBA with sufficient privileges to read the tables and views needed to build the required OLAP objects.
IF the DBA objects to a reporting system being given access to "their" database then this is usually overcome with good requirements documentation where the required queries are listed out. (Yes it can be a chicken and egg problem sometimes in that without access to the tables how do you specify a query! But there's usually a way around it via a dev or test system.)
SAP is the only ERP that makes this process really (and I mean REALLY) difficult, but there are a few SAP Connectors available that can overcome this and make it quite easy.
With the exception of SAP you don't need a connector, just like you don't need a staging DB. Sure being able to connect to a DWH wit a star schema with pre-built dimension tables will make life much easier to build dimensions and cubes in TM1 but it isn't a necessary pre-condition.