Today I want to write interesting detail, which was strange for me.
Imagine situation, that you in Extention class want to change some behaviour and want to ask something from view in base graph. You can try to do it with Base.BaseViewName.Cache.Current. And according to my observations it works. But as mentioned in T300 manual To query a data view declared within the base BLC or lower-level extension from the data view delegate, you should redeclare the data view within the BLC extension.
If you want to ask why this copy/paste needed I honestly will tell you: I don't know :)