When talking about queries and their relevance, we can't omit information about scoring and where it comes from. But what is the score? The score is a parameter that describes the relevance of a document against a query. In the following section, we will discuss the default Apache Lucene scoring mechanism, the TF/IDF algorithm, and how it affects the returned document.
Note
The TF/IDF algorithm is not the only available algorithm exposed by Elasticsearch. For more information about available models, refer to the Different similarity models section in Chapter 2, Indexing Your Data, and our book, Mastering ElasticSearch, Packt Publishing.
When a document is returned by Lucene, it means that Lucene matched the query we sent and that document has been given a score. The higher the score, the more relevant the document is from the search engine point of view. However, the score calculated for the same document on two different queries...