The first clause qualifies the second, standing semantically in an adverbial relationship to it. The logic of qualifying compound sentences seems to be a simple extension of coordinate compound sentences in which what is expressed in the first clause precedes what is expressed in the second. There are several types depending on how the first clause qualifies the second such as ones with quantifying first clauses, interrogative first clauses, conditional first clauses, and those with modal first clauses. (Suttles, 2003, pp. 147-150)
Suttles, W. (2004). Musqueum reference grammar. UBC Press. SFU Student Access.