For a computer, a text is just a string of characters with no particular structure imposed on it. Hence, we call texts unstructured data. However, to humans, texts certainly has a structure, which we use to understand the content. What IR and NLP models try to do is similar: they find the structure in texts, use it to extract the information there, and understand what the text is about.
The simplest possible way of achieving it is called Bag of Words: we take a text, split it into individual words (which we call tokens), and then represent the text as an unordered collection of tokens along with some weights associated with each token.
Let us consider an example. If we take a document, that consists ...
