Refer : http://nti.btk.pte.hu/dogitamas/BHF_FILES/html/90Szecsenyi/Chapter6 for IP's and DP's.

Determiner Phrases: A phrase headed by a central determiner or a possessive -s morpheme. The compliment of a DP is an NP, the specifier the DP the possessive ending attaches to. Inflectional Phrases: In the traditional grammars the IP is a phrase headed by an inflectional element which can be a model auxiliary ( e.g. may, should, will ) infinitival to or the bound morphemes expressing Tense ( ed, s ) the latter undergoing Affix Lowering to for a unit with the verb. In the present approach, however, it has been argued that the head position of the IP contains only the model auxiliary (in English) and the invisible agreement morpheme. Information about Tense can be found in an independent Verb Phrase hosting infinitival to , and the bound morphemes -ed and -s also appear here. The specifier position of an IP is occupied by the Subject (see canonical subject position), the complement of an Inflection is usually a Verb Phrase ( see small phrases for an exception ). IP's are complements of Complementiser Phrases.