"The firefighter saved a kid from the fire."
I've just learnt a sort of curious notion. Generally, it is said that 'the firefighter' is a noun phrase "NP". But, somaone said that's a determinative phrase "DP". Surely, I don't know syntax expertly and technically. To the best of my knowledge, if it's "NP", the head of the phrase is "firefighter". Contrariwise, If it's "DP", the head of the phrase is "the", firefighter being complement of "the". Ergo, the intense curiosity makes me say that between a determinative and a noun, which one do you native speakers think of firstly when you enunciate "The firefighter"?