diff --git a/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/Book.kt b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/Book.kt
new file mode 100644
index 00000000..8c27b74c
--- /dev/null
+++ b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/Book.kt
@@ -0,0 +1,90 @@
+package com.intelligentbackpack.desktopdomain.entities
+
+import com.intelligentbackpack.desktopdomain.entities.implementations.BookImpl
+import com.intelligentbackpack.desktopdomain.exception.ISBNException
+import com.intelligentbackpack.desktopdomain.policies.ISBNPolicy
+
+interface Book {
+    /**
+     * The ISBN of the book.
+     */
+    val isbn: String
+
+    /**
+     * The title of the book.
+     */
+    val title: String
+
+    /**
+     * The authors of the book.
+     */
+    val authors: Set<String>
+
+    companion object {
+
+        /**
+         * Builds a book copy.
+         *
+         * @param block The builder block.
+         * @return The book copy built.
+         * @throws IllegalArgumentException If the book title is black or the authors are blanck.
+         * @throws ISBNException If the ISBN of the book is not valid.
+         * @throws IllegalStateException If not all the properties are initialized.
+         */
+        inline fun build(
+            block: Builder.() -> Unit
+        ): Book = Builder().apply(block).build()
+    }
+
+    class Builder {
+
+        /**
+         * The ISBN of the book.
+         */
+        lateinit var isbn: String
+
+        /**
+         * The title of the book.
+         */
+        lateinit var title: String
+
+        /**
+         * The authors of the book.
+         */
+        lateinit var authors: Set<String>
+
+        /**
+         * Builds the school supply.
+         *
+         * @return The school supply built.
+         * @throws IllegalStateException If not all properties are initialized.
+         * @throws IllegalArgumentException for any other reason.
+         * @throws ISBNException If the ISBN of the book is not valid.
+         */
+        @Throws(
+            IllegalStateException::class,
+            ISBNException::class,
+            IllegalArgumentException::class
+        )
+        fun build(): Book =
+            if (this::isbn.isInitialized &&
+                this::title.isInitialized &&
+                this::authors.isInitialized
+            )
+                if (title.isNotBlank() &&
+                    authors.all { it.isNotBlank() }
+                )
+                    if (ISBNPolicy.isValid(isbn)) {
+                        BookImpl(
+                            isbn = isbn,
+                            title = title,
+                            authors = authors
+                        )
+                    } else
+                        throw ISBNException()
+                else
+                    throw IllegalStateException("Not all properties are initialized")
+            else
+                throw IllegalStateException("Not all properties are initialized")
+    }
+}
diff --git a/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/BookCopy.kt b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/BookCopy.kt
index 6f5650cb..a29a0c2a 100644
--- a/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/BookCopy.kt
+++ b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/BookCopy.kt
@@ -4,27 +4,13 @@ import com.intelligentbackpack.desktopdomain.entities.implementations.BookCopyIm
 import com.intelligentbackpack.desktopdomain.exception.ISBNException
 import com.intelligentbackpack.desktopdomain.exception.RFIDFormatException
 import com.intelligentbackpack.desktopdomain.exception.TypeException
-import com.intelligentbackpack.desktopdomain.policies.ISBNPolicy
 import com.intelligentbackpack.desktopdomain.policies.RFIDPolicy
 
 /**
  * Interface for a book copy.
  */
 interface BookCopy : SchoolSupply {
-    /**
-     * The ISBN of the book.
-     */
-    val isbn: String
-
-    /**
-     * The title of the book.
-     */
-    val title: String
-
-    /**
-     * The authors of the book.
-     */
-    val authors: List<String>
+    val book: Book
 
     companion object {
 
@@ -34,7 +20,6 @@ interface BookCopy : SchoolSupply {
          * @param block The builder block.
          * @return The book copy built.
          * @throws IllegalArgumentException If the book copy is invalid
-         * ( the [isbn] doesn't match with the [ISBNPolicy],
          * the [rfidCode] doesn't match with the [RFIDPolicy],
          * @throws IllegalStateException If not all the properties are initialized.
          */
@@ -47,8 +32,6 @@ interface BookCopy : SchoolSupply {
      * Builder for a book copy.
      * The [type] is automatically set to [SchoolSupplyTypes.BOOK].
      *
-     * @property checkSubjects The subjects that are available.
-     *
      */
     class Builder {
 
@@ -58,19 +41,9 @@ interface BookCopy : SchoolSupply {
         lateinit var rfidCode: String
 
         /**
-         * The ISBN of the book.
-         */
-        lateinit var isbn: String
-
-        /**
-         * The title of the book.
+         * The book of the copy.
          */
-        lateinit var title: String
-
-        /**
-         * The authors of the book.
-         */
-        lateinit var authors: List<String>
+        lateinit var book: Book
 
         /**
          * The type of the school supply.
@@ -84,43 +57,27 @@ interface BookCopy : SchoolSupply {
          * @throws IllegalStateException If not all properties are initialized.
          * @throws TypeException If the type of the school supply is not valid.
          * @throws RFIDFormatException If the RFID code of the school supply is not valid.
-         * @throws IllegalArgumentException for any other reason.
          * @throws ISBNException If the ISBN of the book is not valid.
          */
         @Throws(
             IllegalStateException::class,
             TypeException::class,
-            RFIDFormatException::class,
-            IllegalArgumentException::class
+            RFIDFormatException::class
         )
         fun build(): BookCopy =
             if (this::rfidCode.isInitialized &&
-                this::isbn.isInitialized &&
-                this::title.isInitialized &&
-                this::authors.isInitialized
+                this::book.isInitialized
             )
-                if (title.isNotBlank() &&
-                    authors.isNotEmpty() &&
-                    authors.all { it.isNotBlank() }
-                )
-                    if (type == SchoolSupplyTypes.BOOK)
-                        if (RFIDPolicy.isValid(rfidCode))
-
-                            if (ISBNPolicy.isValid(isbn)) {
-                                BookCopyImpl(
-                                    rfidCode = rfidCode,
-                                    isbn = isbn,
-                                    title = title,
-                                    authors = authors
-                                )
-                            } else
-                                throw ISBNException()
-                        else
-                            throw RFIDFormatException()
+                if (type == SchoolSupplyTypes.BOOK)
+                    if (RFIDPolicy.isValid(rfidCode))
+                        BookCopyImpl(
+                            rfidCode = rfidCode,
+                            book = book
+                        )
                     else
-                        throw TypeException(type)
+                        throw RFIDFormatException()
                 else
-                    throw IllegalStateException("Not all properties are initialized")
+                    throw TypeException(type)
             else
                 throw IllegalStateException("Not all properties are initialized")
     }
diff --git a/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/implementations/BookCopyImpl.kt b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/implementations/BookCopyImpl.kt
index 2a8145ec..5558833c 100644
--- a/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/implementations/BookCopyImpl.kt
+++ b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/implementations/BookCopyImpl.kt
@@ -1,5 +1,6 @@
 package com.intelligentbackpack.desktopdomain.entities.implementations
 
+import com.intelligentbackpack.desktopdomain.entities.Book
 import com.intelligentbackpack.desktopdomain.entities.BookCopy
 import com.intelligentbackpack.desktopdomain.entities.SchoolSupplyType
 import com.intelligentbackpack.desktopdomain.entities.SchoolSupplyTypes
@@ -8,31 +9,21 @@ import com.intelligentbackpack.desktopdomain.entities.SchoolSupplyTypes
  * Implementation of a book copy.
  *
  * @property rfidCode The RFID code of the book copy.
- * @property isbn The ISBN of the book copy.
- * @property title The title of the book copy.
- * @property authors The authors of the book copy.
+ * @property book The book of the copy.
  * @property type is automatically set to [SchoolSupplyTypes.BOOK].
  */
 internal data class BookCopyImpl(
     override val rfidCode: String,
 ) : BookCopy {
 
-    override lateinit var isbn: String
-        private set
-    override lateinit var title: String
-        private set
-    override lateinit var authors: List<String>
+    override lateinit var book: Book
         private set
 
     constructor(
         rfidCode: String,
-        isbn: String,
-        title: String,
-        authors: List<String>,
+        book: Book
     ) : this(rfidCode) {
-        this.isbn = isbn
-        this.title = title
-        this.authors = authors
+        this.book = book
     }
 
     override val type: SchoolSupplyType = SchoolSupplyTypes.BOOK
diff --git a/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/implementations/BookImpl.kt b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/implementations/BookImpl.kt
new file mode 100644
index 00000000..aed62432
--- /dev/null
+++ b/desktopDomain/src/main/kotlin/com/intelligentbackpack/desktopdomain/entities/implementations/BookImpl.kt
@@ -0,0 +1,18 @@
+package com.intelligentbackpack.desktopdomain.entities.implementations
+
+import com.intelligentbackpack.desktopdomain.entities.Book
+
+data class BookImpl(
+    override val isbn: String
+) : Book {
+    override lateinit var title: String
+        private set
+
+    override lateinit var authors: Set<String>
+        private set
+
+    constructor(isbn: String, title: String, authors: Set<String>) : this(isbn) {
+        this.title = title
+        this.authors = authors
+    }
+}