Ofer Mendelevitch for Hortonworks blog:
Hadoop is different. A schema is not needed when you write data; instead the schema is applied when using the data for some application, thus the concept of “schema on read”.
Most often when speaking about Hadoop, people refer to costs (commodity servers), parallelism and scalability. I do not remember how many times I’ve written that the main difference between Hadoop and traditional data warehouses is in the agility it offers.
One Hadoop tagline could be: “collect data today. analyse it when and how you want“.
Original title and link: Schema on Writes vs Schema on Reads - Apache Hadoop and Data Agility ( ©myNoSQL)