Explain how binding works

Data binding is the process of copying the data from one object to another object. It provides a convenient way to pass data around in an application. Adobe Flex 2 provides three ways to specify data binding: the curly braces ({}) syntax and the tag in MXML and the BindingUtils methods in ActionScript.
Data binding requires a source property, a destination property, and a triggering event that indicates when to copy the data from the source to the destination. To use a property as the source of a data binding expression, the component must be implemented to support data binding, which means that the component dispatches an event when the value of the property changes to trigger the binding.
At compile time, the MXML compiler generates code to create ActionScript Watcher and Binding objects that correspond to the binding tags and expressions found in an MXML document. At run time, Watcher objects are triggered by change events that come from the constituent parts of binding source expressions; the Watcher objects then trigger Binding objects to execute bindings.
When we specify a property as the source of a data binding, Flex monitors not only that property for changes, but also the chain of properties leading up to it. The entire chain of properties, including the destination property, is called a “bindable property chain“. In the following example, firstName.text is a bindable property chain that includes both a firstName object and its text property:
{firstName.text}
It’s not necessary that the binding executes automatically. In the following case the binding wont execute automatically as expected.
1. Binding does not execute automatically when we change an entire item of a dataProvider property.
2. Binding also does not execute automatically for subproperties of properties that have [Bindable] metadata.
3. Binding also does not execute automatically when we are binding data to a property that Flash Player updates automatically, such as the mouseX property.
The executeBindings() method of the UIComponent class executes all the bindings for which a UIComponent object is the destination. All containers and controls, as well as the Repeater component, extend the UIComponent class. The executeChildBindings() method of the Container and Repeater classes executes all of the bindings for which the child UIComponent components of a Container or Repeater class are destinations. All containers extend the Container class. However, we should only use the executeBindings() method when we are sure that bindings do not execute automatically.