While this chapter has hopefully given you some good insight into how to extract useful information from unstructured text, it’s barely scratched the surface of the most fundamental concepts, both in terms of theory and engineering considerations. Information retrieval is literally a multibillion-dollar industry, so you can only imagine the amount of combined investment that goes into both the theory and implementations that work at scale to power search engines such as Google and Yahoo!. This section is a modest attempt to make sure you’re aware of some of the inherent limitations of TF-IDF, cosine similarity, and other concepts introduced in this chapter, with the hopes that it will be beneficial in ....