JCR 2.0 is based on 283 JSR specifications and Sling allows persisting content and data without any transformation or translation without any schema.
SOLR: is again can have massive scalable storage system without rigid schema better result than RDBMS a substitute to any NoSQL Database
RDBMS: Needless to describe its most suitable for Transaction application where data has relations however NoSQL systems are challenging it now and their monopoly in the last decades is coming to an end. And it’s just time: I can’t even count the things that were forced into relational databases
Software Architects to choose the appropriate one for a project right at the beginning.
Hundreds of RDBMS vendors are into market for many decades the differences between NoSQL databases are much bigger than ever was between one SQL database and another.
But in terms of RDBMS Database where content/data has relation you can choose any RDBMS on 1st level of investigation. But the same does not apply on NoSQL. Let me list down major NoSQL vendor systems.
MongoDB, Riak, CouchDB ,Redis HBase,Cassandra, Hypertable, Accumulo ,Neo4J, ElasticSearch, CouchBase , VoltDB, Scalaris, Kyto Tycoon.
Each has certain business focus and requirement and none of them can be picked randomly