In the Alapin System White´s strategic idea is extremely simple. He prepares to advance with d2-d4, to build a solid pawn centre and then dictate the play. He will have to pay for this with the fact that his queen´s knight has been deprived of the best square for its development, but it may have other suitable squares (in many variations this will be not the d2-square but a3).
Secondly, it very often happens that after d4 cxd4 cxd4, White's queen's knight still gets access to its best square on c3. The modern evaluation of this system is that Black has comfortable enough lines in which he can obtain an acceptable game.
The authors try to prove that not all of these lines are equally good.