In this chapter, we gave an overview of Lucene, discussing how it works, how the analysis process is done, and how to use the Apache Lucene query language. In addition to that, we discussed the basic concepts of Elasticsearch.
We also introduced Elasticsearch 5.x and covered the latest features introduced in version 2.x as well as 5.x. Finally, we talked about the most important changes and removal of features that Elasticsearch has implemented during the transition from 1.x to 5.x.
In the next chapter, you will learn about the new default scoring algorithm, BM25, and how it is better than the previous TF-IDF algorithm. In addition to that, we will discuss various Elasticsearch features, such as query rewriting, query templates, changes in query modules, and various queries to choose from, in a given scenario.