C# Events and Delegates

Difference between C# events and delegates
Recently i was wondering about the difference between C# delegates and events. For me events seemed to be a very thin wrapper around delegates. I have been trying to find out the advantage that the keyword "event" adds. I have to explore more on this aspect. But here i present a simple example containing a publisher, a subscriber, and an event broker.

using System;
namespace Test
{
class Publisher
{
private EventBroker evtBroker;
public void RegisterWithBroker(EventBroker evtBroker)
{
this.evtBroker = evtBroker;
}

public void Publish(string message)
{
this.evtBroker.Notify(message); // <---- statement 1
//this.evtBroker.handler(message); // <---- statement 2
}
}

class EventBroker
{
public delegate void onEvent(string message);
public event onEvent handler; //<---- statement 3
//public onEvent handler; //<--- statement4-a simple delegate

//will be used by puiblishers
public void Notify(string message)
{
handler(message);
}

// //this call is used to subscribe
public void RegisterSubscriber(onEvent handler)
{
this.handler += handler;
}
}

class Subscriber
{
public void ReceivedMessage(string message)
{
Console.WriteLine("Received Message: "+message);
}
}

class Test
{
[STAThread]
static void Main(string[] args)
{
EventBroker broker = new EventBroker();
Subscriber sub1 = new Subscriber();
Subscriber sub2 = new Subscriber();

broker.RegisterSubscriber(new EventBroker.onEvent(sub1.ReceivedMessage));
broker.RegisterSubscriber(new EventBroker.onEvent(sub2.ReceivedMessage));


Publisher pub = new Publisher();
pub.RegisterWithBroker(broker);

pub.Publish("Hello to all subscribers");
}
}
}

The important point to note here is that if you comment out 'statement1' and un-comment 'statement2'. Then you would get a complier error that the event handler can be invoked (raised) only inside the 'EventBroker' which defines it. 'Statement 4' defines the delegate, now if i comment out statement 1 and 3 and un-comment statement 2 and 4. The code works perfectly.

The event i believe has an extra constrain that it can only be invoked from within the class which defines it. Hence the class defining an event should define a method like "Notify" to facilitate other classes raise the event. I believe there are other differences...i just hit upon this one..will look for others...