Discipline - "a field of study"
-- Merriam-Webster Dictionary
Every field of study has it's own unique history and set of values. As you study in any discipline, you should pay close attention to how information structures evolved and which information sources are considered authoritative.
Books remain prestigious in disciplines like history and philosophy in which scholars present their ideas in long form.
Math and many sciences generally favor articles in peer reviewed journals.
The social sciences might go either way depending on the area of specialization.
Traditional Model - Subscriptions sold to Libraries
The Open Access Movement