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Object Diagrams for Library Management System: A Visual Guide



Object Diagrams for Library Management System: A Visual Guide




Object diagrams are a type of UML diagram that show the instances of classes and their relationships at a specific point in time. They are useful for illustrating the state of a system during a scenario or a use case. Object diagrams can also show the values of attributes and the links between objects.




object diagrams for library management system



In this article, we will see how to create object diagrams for a library management system, which is a software that manages the books, members, and transactions of a library. We will use some examples from existing UML diagrams for library management system that are available online[^1^] [^2^] [^3^]. We will also explain the notation and symbols used in object diagrams.


What are the components of an object diagram?




An object diagram consists of the following components:


Objects: Objects are instances of classes that have a name, a colon, and an optional classifier. For example, librarian: Librarian is an object named librarian that is an instance of the Librarian class. Objects can also have values for their attributes, which are shown below the name. For example, librarian: Librarian


  • name = "Alice" shows that the librarian object has an attribute name with the value "Alice".



  • Links: Links are connections between objects that represent their relationships. Links can have names, roles, multiplicities, and constraints. For example, librarian -- issues --> bookItem: BookItem is a link named issues that connects the librarian object to the bookItem object with a role of BookItem. The multiplicity of this link is one-to-many, meaning that one librarian can issue many book items, but one book item can only be issued by one librarian. The constraint of this link is shown by a dashed line with an xor notation, meaning that the book item can either be issued or reserved, but not both.



Link objects: Link objects are instances of association classes that represent the properties of a link. Link objects have a name, a colon, and a classifier that is the name of the association class. For example, issueRecord: Issue is a link object named issueRecord that is an instance of the Issue association class. Link objects can also have values for their attributes, which are shown below the name. For example, issueRecord: Issue


issueDate = "01/01/2020"


  • dueDate = "15/01/2020" shows that the issueRecord object has attributes issueDate and dueDate with the values "01/01/2020" and "15/01/2020" respectively.



How to create object diagrams for library management system?




To create object diagrams for library management system, we need to identify the objects, links, and link objects that are relevant for the scenario or use case we want to illustrate. We can use the class diagram for library management system as a reference to find out the classes and their associations. We can also use the sequence diagram or activity diagram for library management system to find out the interactions and behaviors of the objects.


For example, let's say we want to create an object diagram for the scenario of checking out a book by a member. We can use the following steps:


Identify the objects involved in this scenario. We can use the class diagram[^3^] to see that there are four classes: Member, Librarian, BookItem, and Issue. We can create four objects from these classes and give them names and values for their attributes. For example:member: Member


name = "Bob"


cardNumber = "1234567890"


totalBooksCheckedOut = 1


librarian: Librarian


name = "Alice"


employeeId = "L001"


bookItem: BookItem


barcode = "B001"


rackNumber = "R001"


isReferenceOnly = false


borrowed = true


issueRecord: Issue


issueDate = "01/01/2020"


  • dueDate = "15/01/2020"

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