“…The former has been studied by far the most, as it provides a direct, powerful and extensive framework, firmly rooted in geometry and string theory. A partial list of references is [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. The alternative approach, based on the four dimensional low energy effective N = 2 supergravity theory, has received considerably less attention, in part because at first sight this effective theory seemed much too simple to be able to capture the intricacies of the D-brane spectrum.…”