We are talking about Data-Intensive Systems. But what is the main purpose of developing a Data-Intensive System? What does a Data-Intensive System really do? You may say it processes the data at scale, but still that's just a step in the actual question that it is trying to answer. A Data-intensive system tries to answer questions based on the data that is either presented to it in real-time, on the data that have been collected in the past, or a combination of both. Big Data, a book by Nathan Marz, defines Data Systems as systems that compute queries that are functions of all the data we've ever seen:
Query = Function(all data)
This definition of a query is at the center of Lambda architecture.
The first thing that should ...