Here's some pointers.
An ordinary relational database is concerned about the relationship between rows and columns of data. That may involve storing the rows of data on disk in certain formats to enable efficient access and extensive indexes and clever algorithms to search for and join data together. Also a database expends a lot of effort on the so called ACID properties. And the primary interface to a RDBMS is SQL. You can look up more details about the theoretical underpinnings of a RDBMS.
So great big chunks of text are not really what an RDBMS is about. It makes little sense in trying to form a relationship between the text of one book and another. So Rdbms tend to have blob objects and store content off on the side. They also may have restrictions on the data size. Fine so far as it goes but the access to the content is via SQL so that can be a bottleneck especially if big volumes of data is being shifted. Remember that SQL is supposed to be about tables of data so its not optimised for streaming content.
So there's another type of database nosql that may help in your content management mission. You may like to consider that as well.
So the content management system like alfresco. Presents the content over lots of different interfaces especially streaming.
Provides higher level functionality such as versioning, transformation, rules, workflow and search. search is a very different beast to SQL.
May provide a user interface. Forms, actions, Timers etc,etc.
May have records management functionality.
Will enable applications like Wcm or case management or digital asset management.
