Too Long; Didn't Read
Elasticsearch and Solr are the most popular and widely used full-text search engines. They are both built on top of Apache Lucene, a high-performance, full-featured text search engine library written in Java. A document is what is stored by the search engine, which is nothing more than a set of properties (named fields) that describe an object. In the next part, we will focus mainly on this last aspect, defining the notion of relevancy, how to measure it, and how to improve it.