Natural Language Processing (NLP) is a part of computer science and computational linguistics that deals with textual data. To a computer, texts are unstructured, and NLP helps find the structure and extract useful information from them.
Information retrieval (IR) is a discipline that studies searching in large unstructured datasets. Typically, these datasets are texts, and the IR systems help users find what they want. Search engines such as Google or Bing are examples of such IR systems: they take in a query and provide a collection of documents ranked according to relevance with respect to the query.
Usually, IR systems use NLP for understanding what the documents are about - so later, when the user needs, these documents can be retrieved. In this chapter, we will go over the basics of text processing for information retrieval.