对于半监督方法，目前存在的一个严重的问题是数据稀疏问题。

The main disadvantage of the way is the problem of data sparsity.

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这两种方法均不受外部资源所限，能在一定程度上解决数据稀疏问题。

These two methods are both not subject to external resource constraints and would solve the data sparse problem in some extent.

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针对协同过滤中的数据稀疏问题，提出了一种基于粗集的协同过滤算法。

Aiming at the problem of data sparsity for collaborative filtering, a novel rough set-based collaborative filtering algorithm is proposed.

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