Why will the next book content providers to build a single project?

Just see below
androidThere is a com.android.contacts

Contacts

There is also a
com.android.providers.contacts
Contributors to the address book content.

In the address book directly outside content not on the list?
And seemingly no address book database, and only applications, and address book is stored in the content database provider in.
In other words,
This book is just manipulate the data in the content provider's address book Why?

The book is the real content providers Apply to save user information.

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Reply:
Your understanding is correct.
Android ContentProvider method of sharing data between different applications. android is based on the Linux kernel, Linux determines the security features can not share data directly between applications. So android implements ContentProvider, similar to a database, there are CRUD functionality.