Hierarchy question

[miwojc]

I am exploring the google open images dateset v6. and it provides a great resource of annotated images. Big thank you for this amazing work!

I have a question regarding to hierarchy. I noticed there are multiple times that human body parts are used. Sometimes it links directly to Entity', sometimes to Body part -> Entityand sometimes toBody part -> Person -> Entity. There will be more similar situations for different classes, for example bicycle helmet, its in multiple parent classes: Helmet -> Sports equipment -> Entity, Helmet -> Sports Equipment -> Building -> Entity' and Helmet -> Clothing -> Entity
I wonder why we have such arrangement please?

Thank you!

Link to hierarchy visualization: https://storage.googleapis.com/openimages/2018_04/bbox_labels_600_hierarchy_visualizer/circle.html