The main difference is that you can update the document variables without fragmenting the index. In Lucene you need to reindex the document (i.e. delete it and

The main difference is that you can update the document variables without fragmenting the index. In Lucene you need to reindex the document (i.e. delete it and write a new one). If you update your relevance variables an average of 10 times per document it can get really fragmented with Lucene.