According to the nature of open-texture, a case can be an easy case or a hard case. If a legal expert system realizes the real legal word, the system is forced to take into consideration the problem of open-texture. But the existing systems almost ignore the open-texture of the law. The open texture of the indicates that a certain process should take place in arguing for and against a decision. Lawyers and judges should refer to the appropriate legal sources.
Computer systems can at least carry out a retrieval of the appropriate legal material.
To decide a case, we can ft imagine how huge the system needs the legal material. CISG case is a part of the legal material. Schild, ibid., p.134.