Here, we’ll create the class diagram for our system on the basis of the requirements that we gathered previously. In the class diagram, we will first design/create the classes, abstract classes, and interfaces for the system, and then we’ll identify the relationship between classes in accordance with all requirements of the library management system.

Components of a library management system

In this section, we will define the classes for LMS. Since we are following the bottom-up approach for designing a class diagram, we’ll first create the classes of small components. After that, we will integrate those components and create the class diagram for the whole library management system.

Book and book item

The Book class represents the conceptual essence of a book. This includes metadata or descriptive information about a book that isn’t specific to any single physical copy. It serves as a blueprint that captures the shared attributes of all instances or copies of the book, whether they exist in the world or within the library’s collection.

The BookItem class, in contrast, represents a specific physical or digital instance of a Book in the library’s collection. Rather than extending the Book, it has a composition relationship with it, meaning each BookItem is tightly associated with a Book. If a Book is deleted, all corresponding BookItem instances must also be deleted. The BookItem class handles the properties and behaviors associated with individual copies that patrons can borrow, reserve, or reference within the library. Each BookItem has unique attributes to manage and track its status within the library system. The UML representation of Book and BookItem is shown in the class diagram below:

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