As opposed to Vaadin 7, the 8th version of the framework encourages the more stateless and lean data binding approaches via DataProvider interface, which is an API revolving around the abstract query concept: the main thing you have to implement is how to fetch a chunk of data (possibly with some filters/sorters applied).
In order to cater for both Grid and TreeGrid , DataProvider comes in flat and hierarchical incarnations, where the latter is similar to the former with a difference, that the queries are executed against some parent item (aka child query).
Overview
Content Tools