A Plain Old CLR Object (POCO) model of a Book with DataAnnotations for validation

Book.cs

using System;
using System.ComponentModel.DataAnnotations;

namespace NanoTaboada.GitHub.Gist
{
    public class Book
    {
        [Key]
        public string Isbn { get; set; }

        [Required]
        public string Title { get; set; }

        public string SubTitle { get; set; }

        [Required]
        public string Author { get; set; }

        public string Publisher { get; set; }

        [Required]
        public DateTime Published { get; set; }

        public int Pages { get; set; }

        [Required]
        public string Description { get; set; }

        [Required]
        [Url]
        public string Website { get; set; }
    }
}