Relevance calculation

Now that we are aware of how Solr works in the creation of an inverted index and how a search returns results for a query from an index, the question that comes to our mind is how Solr or Lucene (the underlying API) decides which documents should be at the top and how the results are sorted. Of course, we can have custom sorting, where we can sort results based on a particular field. However, how does sorting occur in the absence of any custom sorting query?

The default sorting mechanism in Solr is known as relevance ranking. During a search, Solr calculates the relevance score of each document in the result set and ranks the documents so that the highest scoring documents move to the top. Scoring is the process of determining how relevant a given document is with respect to the input query. The default scoring mechanism is a mix of the Boolean model and the Vector Space Model (VSM) of information retrieval. The binary model is used to figure out documents that match...