Bonhoeffers dogma

The title of Bonhoeffers first book, "Sanctorum Communio,
Eine dogmatische Untersuchung zur Soziologie der Kirche"
which I translate as "The communion of saints, a dogmatic
investigation pertaining to the sociology of the church,"
suggests to me a set of questions with which I ask your
help.

Since I have no theological training, I ask, What is a
dogmatic investigation?  What characterizes a dogmatic
investigation as distinct from other types of investigations,
for example empirical, analytic, synthetic, dialetical,
aporetic, phenomenological or existential ones?
Do Bonhoeffer's subsequent books, "Akt und Sein", "Nachfolge",
"Schoepfung und Fall", for example, share the dogmatism of
"Sanctorum Communio"?  Does a dogmatic investigation preclude
a dialectical or an aporetic approach to the topic investigated?