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Mark Glasser, the OVM Cookbook author writes,
"OVM testbenches are organized in layers. The bottommost layer is the DUT, an RTL device with pin-level interfaces. Above that is a layer of transactors, devices that convert between the transaction-level and pin-level worlds. The components in the layers above the transactor layer are all transaction-level components. The diagram below illustrates the layered testbench organization. The box on the left identifies the name of the layer. The box on the right lists the type of components in that layer. The vertical arrows show which layers communicate directly. For example, the control layer communicates with the analysis, operational, and transactor layers, but not directly with the DUT."
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