It’s worth following the link below to read the entire post, about how Hadoop, a linchpin of many NoSQL products and attitudes, now must coexist with SQL, and some of the most Hadoop-centric vendors are moving aggressively in this direction. Here, I’ll just call attention to what sounds like an actual repository. The pendulum swings back.
The point about this is that if you want to comnect to a mix of NoSQL DBMSs, Hadoop and Analytical RDBMSs as well as Data Warehouses, On-Line Transaction Processing Systems and other data then you very quickly start to need the ability to know where the data is in underlying systems. A global catalog is needed so that software knows that it needs to invoke underlying MapReduce jobs to get at Data in Hadoop HDFS, or that it accesses it directly by bypassing MapReduce via Impala for example.