A property of this node is its unique identifier — a 1 to 12 character label.
此结点有一个属性，即它的唯一标识符——由1到12个字符组成的标签。
2
The key attribute is functioning as a label on the address_rec container to provide a unique identifier for the record.
key属性的作用是充当address_rec容器上的一个标签，为记录提供一个惟一的标识符。
3
Once you have the artist identifier, you'll want to show users the human-readable name than the URI identifier, so the query asks for the RDFS: label that goes with that artist identifier.