The World Atlas of Language Structures Online

Basque should definitely (!) be placed under the category "definite affix". The relevant sentences are to be found in Saltarelli et al. p.198, Section 2.1.1.8.1.: "The number marker is usually -0 for indefinite NPs, -a for definite singular NPs, -ak for definite plural absolutive NPs, and -e for definite plural ergative NPs. For inanimate locative NPs, the indefinite and definite plural forms are marked by the suffix -ta-".
Anyway, this should suffice to explain that it is impossible to speak of an "article word", and consequently, Basque must be given the category "article affix".