A ConnectionMixin class dictates how a data source connects to its data.
This can vary depending on the URI, and so this class grabs the appropriate
mixin based on the original URI. It isn't always the case that a connection mixin
will exist for this URI, if the data source implicitely provides it's own
connection, it won't need this. This is generally the case for non-string
based connections. If the data source does provide it's own connection information,
this should be ignored, because it will probably not return the correct type