This chapter began with a discussion on relation databases. You've learned that the DBI package defines a standard interface on which various database drivers build upon. You then learned how to query these types of databases, and to load the results in R.
Next, you gained an appreciation for JSON and XML (right?), and how to approach the importing of data from these formats. We then put our chops to the test by wielding data provided to us by two different web service APIs.
I stealthily snuck in some fancy new R constructs in this chapter. For example, prior to this chapter, we never explicitly worked with lists before.
Finally, you learned about how to look for information beyond which this chapter can provide, and some other places ...