Consider a database schema consisting of the following relational schemes:

author_pub (_author_id_, _pub_id_, author_position) -Refers to author Publisher author (_author_id_, last_name, first_name) Describes Author pub (_pub_id_, _book_id_, title) Gives information about Publisher book (_book_id_, year, editor, book_title, month) Describes Book

author_id in author_pub is a foreign key referencing author. pub_id in author_ pub is a foreign key referencing pub. book_id in pub is a foreign key referencing book. editor in book is a foreign key referencing author (author_id). Primary keys are _underlined_.

1. What question does the following expression answer? | author_id(author) editor(book)|

2. With the help of relational algebra expression find the names of all authors who are book editors.

3. Write the relational algebra expression that return the name of all authors who are not book editors.

4. Using relational algebra expression find the name of all authors who have at least one publication in the database.

5. What question does the following relational algebra expression answer?

author * (author-pub * (omonth-July' (book) * pub)) month T JU