Can で be used to define a family relationship?

Question

天帝の娘ではたを織るのが上手だったおり姫と牛飼いのひこ星はおたがいに好きになり、結婚する。
??? Princess Ori, who was skilled with the weaving, and Hikoboshi the cowherd come to love each other and will get married.

Now, I'm assuming that the で in bold somehow tells us that Princess Ori is the daughter of the Sky King. But, this doesn't fit with my usual understanding of で as either a location marker, 'by means of', or て-form of copula.

Have I understood the meaning correctly? Can you please give some more examples of how/when I should use で in this way?

Answer 1

The で is the te-form of the copula (or, the continuative form of the assertive auxiliary) だ.

［天帝の娘で］［はたを織るのが上手だった］おり姫
Princess Ori, [who was the daughter of the Sky King and] [was skilled with the weaving]

To turn this noun phrase into its non-relative equivalent:

おり姫は、天帝の娘で、はたを織るのが上手だった。
Princess Ori was the daughter of the Sky King and was skilled with the weaving.
(≂ おり姫は、天帝の娘だった。おり姫は、はたを織るのが上手だった。)

Example:

太郎は花子の弟だ。+ 太郎は東京の大学に通っている。
→太郎は花子の弟で、東京の大学に通っている。
→花子の弟で、東京の大学に通っている太郎 (noun phrase)