The second example – an information retrieval search tool
According to Wikipedia (https://en.wikipedia.org/wiki/Information_retrieval), information retrieval is:
"The activity obtaining information resources relevant to an information need from a collection of information resources."
Usually, the information resources are a collection of documents and the information need is a set of words, which summarizes our need. To make a fast search over the document collection, we use a data structure named inverted index. It stores all the words of the document collection, and for each word, a list of the documents that contains that word. In Chapter 4, Getting Data from the Tasks – The Callable and Future Interfaces, you constructed an inverted index of ...