Necromancy

Necromancy is a practice of magic deemed taboo and outright forbidden by most of sorcerer society. It is at its basis magic that is able to restore life to the dead. However, this is not a direct method of simply bringing the dead back to life but more the method of regenerating the body and reversing decay and necrosis to the point the body is viable again. Though not much is specified in its regard it is presumably a combination of Diamond and Emerald Magics based on its focus of healing the body and manipulating the soul of the dead. It also likely includes some elements of Blood Magic based on its corruptive and taboo nature. 
While the power to revive the dead is tempting beyond most others it is forbidden because it is unnatural and corruptive. It's been stated that attempting to resurrect someone or something without a fully intact Soul will result only in an abomination. Since a soul of a living creature exits the body and shatters as it fades into the afterlife it is nearly impossible to obtain a full living soul to do this and there is no known way to resurrect even part of a soul. Now it could be possible that if someone were to be killed in a way that damaged their body beyond any hope of healing with medicine or magic and a sorcerer with the right know how was nearby, they could capture the soul of the dying body before it shattered and then hold it to be given a new viable body or long enough for its original to be healed but this is a rather rare possibility and not directly a case of Necromancy. In addition to this there's been mentioned that a body revived by Necromancy can possibly become zombie like based on Isabelle asking Alistair if a dog he revived with Necromancy was "Going to eat her brains?". Though this is never seen it is possible this is the result of simply reviving a body but leaving it without a soul making it a brainless zombie like living corpse. These side effects and draw backs combined make Necromancy rather impractical in common use if not outright impossible but there have been ways explained that can circumvent or cheat the rules in certain cases to come in handy. 
While it seems impossible to revive a soul that has fully passed on to the afterlife, as evidenced by Alistair reviving Claire Dupont's dead dog Raven, it is possible to duplicate another less complex soul like that of a dog (or presumably any non-magical animal) and place that soul within the revived body. In this way the body is revived and since an animal's soul is less complex than that of sentient human soul there's little noticeable difference in the revived animals' behavior. Thus, it is more practical to revive a dead animal or pet in this way using necromancy but no known use of Necromancy on a human has ever worked (at least to any degree that would be considered a success). Despite this there have been attempts mentioned at reviving other people with Necromancy. In the case of Lorraine Rose attempting to use it to revive her dead daughter Caroline despite her own husband insisting it was fruitless and dangerous. While she never went too far and seemed to realize it would not work, she was implied to try but stop before she suffered the irreparable corruptive side effects. While she did stop pursuing genuine necromancy, she did turn to using other combinations of magic to attempt to recreate her daughter through her lingering soul fragments and another living body in the form of Oliver Thompson, but this practice did not seem to be a form of Necromancy. Another prominent example of this would be in the form of Sylvana Huntington attempting to revive her dead daughter Amber after she was killed by Non-Bloods. However, in Sylvana's case she went too far, likely due to her stronger power, and she became corrupted to the point of madness. No known success in reviving Amber has been mentioned and it is presumed to have little to no effect. 
Overall Necromancy does seem to have its uses in reviving animals to possibly reviving someone so long as their soul remains fully intact and held on the mortal plain but genuinely attempting to use it to revive someone's who's souls have fully passed on has shown no true success and only serves to corrupt those who try.