Описать класс записная книжка

public class record
    {
        public int id;
        public string Name;
        public string Surname;
        public DateTime Birthday;
        public string PhoneNumber;
 
        public record(int id, string Name, string Surname, DateTime Birthday, string PhoneNumber)
        {
            this.id = id;
            this.Name = Name;
            this.Surname = Surname;
            this.Birthday = Birthday;
            this.PhoneNumber = PhoneNumber;
        }
    }
 
    public class Notebook
    {
        private List<record> notebookRecords;
        public List<record> NotebookRecords
        {
            get { return notebookRecords; }
            set { notebookRecords = value; }
        }
 
        public Notebook()
        {
            notebookRecords = new List<record>();
        }
 
        public List<record> SearchRecords(string Name, string Surname, DateTime? Birthday, string PhoneNumber)
        {
            List<record> ret = new List<record>();
            foreach (record rec in notebookRecords)
                if (rec.Name == Name || rec.Surname == Surname || rec.Birthday == Birthday || rec.PhoneNumber == PhoneNumber)
                    ret.Add(rec);
            return ret;
        }
 
        public void AddRecord(int id, string Name, string Surname, DateTime Birthday, string PhoneNumber)
        {
            record rec = new record(id, Name, Surname, Birthday, PhoneNumber);
            notebookRecords.Add(rec);
        }
 
        public void DeleteRecords(string Name, string Surname, DateTime Birthday, string PhoneNumber)
        {
            List<record> records = SearchRecords(Name, Surname, Birthday, PhoneNumber);
            foreach (record rec in records)
                notebookRecords.Remove(rec);
        }
 
        public void SortBySurname()
        {
            notebookRecords.OrderBy(x => x.Surname);
        }
 
        private void test()
        {
            SearchRecords(null,null,null,null); //вернёт все записи
        }
    }