Consider a database schema consisting of the following relational schemes: - aut

Question

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 (month=’July’(book) pub))|

Explanation / Answer

1) Getting all authors by author_id and who are noy book editors.

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2) last_name(author) AND editor(book)   
** selecting all authors with condition that author should be an book editor.

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3) | last_name(author) editor(book)|
*** return the name of all authors who are not book editors.

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4) |author(author_pub (pub_id(book) pub)) > 0|
**** find the name of all authors who have at least one publication in the database.

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5) Finding names of all authors who have published book in month of july.

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