Data availability is the extent to which suitable examples and target annotations exist for developing a predictive model. It often limits whether a machine-learning problem is feasible: a system can learn sentiment classification only when both movie reviews and sentiment annotations are available. section 6.1.1
Movie-review sentiment classification
Before choosing a model, check whether the project has review texts paired with sentiment labels. If those annotations do not exist, collecting and annotating a dataset becomes necessary. section 6.1.1

