感觉和 Tom M. Mitchell的定义几乎一致, A computer program is said to learn from experience E with respect to some class of tasks T and performance measure P, if its performance at tasks in T, as measured by P, improves with experience E. 简而言之,就是我们想要机器在某些方面有提高(如搜索排名的质量,即NDCG提高),就给机器一些数据(用户的点击数据等各种)然后让机器获得某些经验(Learning to rank的一种模型,也就是数学公式)。这里有点需要强调,那就是提高指标,必须要有某种指标可以量化这种提高,这点还是很关键的,工业界做机器学****首先关注data,其次就是有无成型的measurement,可以使Precision/Recall,也可以是NDCG等。