Design an ER diagram for an online bookstore. Consider that a book can contain multiple works by different authors, a work can be in different books, and there should be a keyword search feature.

For an online bookstore considering the requirements, the following ER diagram can be designed:

• Table Book — stores information about the book (ID, title, publisher, year of publication, etc.).
• Table Work — individual works that can be part of one or multiple books.
• Table Author — authors of the works.
• Relationship BookWork — many-to-many between books and works (one book contains multiple works, one work can be in different books).
• Relationship WorkAuthor — many-to-many between works and authors (a work can have multiple authors).
• Table Keyword — keywords for search.
• Relationship WorkKeyword — many-to-many between works and keywords.

Example structure:

Book (BookID PK, Title, Publisher, Year)
Work (WorkID PK, Title, Description)
Author (AuthorID PK, Name)
Keyword (KeywordID PK, Word)

BookWork (BookID FK, WorkID FK)
WorkAuthor (WorkID FK, AuthorID FK)
WorkKeyword (WorkID FK, KeywordID FK)

This design provides:

• Flexibility in linking books and works.
• Support for multiple authors for a single work.
• The ability to search by keywords associated with works.

For keyword search, indexes can be used on the Keyword table and its relationships with Work.