StringParameter.cs

public interface IStringParameter {
    public int Id { get; }
    public string Key { get; }
}

public abstract class StringParameter : IStringParameter
{
    public abstract int Id { get; }
    public abstract string Key { get; }
    public abstract string Description { get; }
    public abstract bool Nullable { get; }
}

public class X : StringParameter {
    public int Id { get { return 42; } }
    [...]
}

// C# 6 and beyond:
public class Y : StringParameter {
    public int Id => 42;
    public string Key => "Foobar";
    [...]
}

public class Z : StringParameter {
    public int Id { get; }
    public string Key { get; }
    
    public Z() {
        Id = 42;
        Key = "Foobar";
    }
}