I have given five examples to illustrate the problems with categorizing da/a as 'copula'. According to the definition in APiCS, the morpheme da (Examples 3, 139) and its variant a (Example 141) can be considered to be copulas because they are practically obligatory before noun phrases. Yet they also occur before definite and referential NPs (Example 138). If they are indeed copulas (which appears doubtful to me because e.g. da precedes the ANT particle me in Example 138), they are also and primarily highlighters, or topic particles in the above sentences, as is clear in Examples 138 and 140.
Source: Escure 2004: 542
Source: Escure's 1992 materials
Source: Escure 1983a: 34
Source: Escure 1993a: 238
Source: Escure 1983a: 37