1. A computing device for generating a natural language understanding (NLU) model for use in a spoken dialog service, the computing device comprising a processor and further comprising: (a) a module that controls the processor to generate and test a first NLU model using a hand crafted rule and sample utterances; (b) a module that controls the processor to build a second NLU model based on the sample utterances as new training data and based on the hand crafted rule; (c) a module that controls the processor to (1) build a series of NLU models by adding a previous batch of labeled data to training data and (2) use a new batch of labeling data as test data to generate the series of NLU models with dynamically increasing training data; and (d) a module that controls the processor, after all the training data is received, at least once, to build a third NLU model based on all the labeling data, wherein the third NLU model is used in a spoken dialog service.