Question

What is the difference between a connected look up and unconnected look up?

Answer 1

When the inputs are taken directly from other transformations in the pipeline it is called connected lookup. While unconnected lookup doesn't take inputs directly from other transformations, but it can be used in any transformations and can be raised as a function using LKP expression. So it can be said that an unconnected lookup can be called multiple times in mapping.

Answer 2

Connected lookup is the one that takes up the input directly from the other transformations and also participates in the data flow. On the other hand, an unconnected lookup is just the opposite. Instead of taking the input from the other transformations, it simply receives the values from the result or the function of the LKP expression.

Connected Lookup cache can be both dynamic and static but unconnected Lookup cache can't be dynamic in nature.  The First one can return to multiple output ports but the latter one returns to only one output port. User-defined values which ads generally default values are supported in the connected lookup but are not supported in the unconnected lookup.