the level of vampires in the "Vampire Knight" universe is determined by their lineage;
vampires would be considered the most powerful(the kings/queens of the vampire world) if no human is found to be in their pedigree;
vampires of few humans as their ancestors would be regarded as nobles--the power they wield is still great, though not as great as the pure-blooded; the more hybrid a vampire is, the lower his/her social status among their species is;
while those would transformed from humans to vampires due to bites from pure-blooded vampires are considered as vampires of the second lowest class, level D, of course, those vampires still has control over their minds--and level Ds who have lost their consience are called level Es.
hope this answers your question.
here's a diagram straight from the comic version of "Vampire Knight":
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(it's in Chinese...happy now?)
[ 此贴被黑澤唯在2008-05-01 19:48重新编辑 ]