The attributes are the properties of an entity that characterize and describe it. Figure below shows the BOOK entity b1 described by the attributes Book_title, Price (in dollars), ISBN, Year, Page_count and Category. Each attribute can accept a value from a set of permitted values, which is called the domain or the value set of the attribute. For example, the domain of the attribute Page_count is a set of positive integers. On the other hand, the category of a book can be a textbook, a language book or a novel. Thus, the domain of the attribute Category is {Textbook, Language book, Novel}. Only one of these three permitted values can be assigned to the category attribute.
First read the answer fully, then try to explain it in your own words. After that, open a few related questions and compare the concepts. This method helps you remember the topic for a longer time and improves exam preparation.