Design a UML class diagram for the Library Book entity, considering the following requirements:

A Library Book has attributes such as "title", "author", "ISBN", "publication year", and "availability".

The "title" and "author" attributes are strings representing the title and author of the book respectively.

The "ISBN" attribute is a unique identifier for the book.

The "publication year" attribute represents the year the book was published.

The "availability" attribute indicates whether the book is available for borrowing or not.

Include appropriate functions.