说明：  DBNs由多个限制玻尔兹曼机（Restricted Boltzmann Machines）层组成。这些网络被“限制”为一个可视层和一个隐层，层间存在连接，但层内的单元间不存在连接。隐层单元被训练去捕捉在可视层表现出来的高阶数据的相关性。
(DBNs are composed of several restricted Boltzmann machines layers. These networks are "limited" to a visual layer and a hidden layer. There is a connection between layers, but there is no connection between units in the layer. The hidden layer unit is trained to capture the high-order data correlation shown in the visual layer.)