"That" identified as having a dependency of "dobj"

[johnosbb]

I am a little confused by how SpaCy parses the following sentence:

"It was a dog that she killed."

Text	Index	POS	Tag	Dep	Dep Detail	Ancestors	Children	Token Head	Sub Tree
It	0	PRON	PRP	nsubj	nominal subject	was		was	It
was	1	AUX	VBD	ROOT	root		It dog .	was	It was a dog that she killed .
a	2	DET	DT	det	determiner	dog was		dog	a
dog	3	NOUN	NN	attr	attribute	was	a killed	was	a dog that she killed
that	4	PRON	WDT	dobj	direct object	killed dog was		killed	that
she	5	PRON	PRP	nsubj	nominal subject	killed dog was		killed	she
killed	6	VERB	VBD	relcl	relative clause modifier	dog was	that she	dog	that she killed
.	7	PUNCT	.	punct	punctuation	was		was	.

The sentence is in the active voice with "dog" being a subject compliment. Why does the Relative Pronoun "that" have a dependency of "dobj"?

[adrianeboyd]

It might be easier to see this from the parse tree:

It's dobj because the relative pronoun is the direct object of "killed".

[johnosbb]

Thank you Adriane. The diagram does help. I think I understand the logic a little better now.

"It" is the subject of the sentence.
"was" is a linking verb that connects the subject "it" to the subject complement "a dog". This tells us that "it" equals "a dog."
"a dog" is the subject complement and the noun being referred to.
"that" introduces a relative clause, providing more information about the noun "dog."
"she killed" is the relative clause, where "she" is the subject and "killed" is the verb.
In the relative clause "that she killed." "that" is serving as a pronoun representing the noun "dog" from the main clause. In the context of the relative clause, "that" is the direct object (dobj) of the verb "killed." It is the thing that the subject "she" is performing the action of killing on.
I think I became too focused on the word to word dependencies and lost sight of the overall relationships of the clauses. The diagram really does help emphasise the relationship.
Thank you again. Your help is much appreciated.