UIA and ARIA

ARIA is the upcoming W3c recommendation/standard for the accessibility of rich internet applications.
So, how does ARIA translate into accessibility?
There are basically four pieces to the accessibility puzzle:
1. ARIA: provides a standardized markup that browser based rich application UI libraries can implement to describe the UI and provide standard events for dynamic updates.
2. The browser: While rendering the apps that have been marked up using ARIA, the browser translates ARIA tags into the platform specific accessibility API. In the case of Windows, this API is now called User Interface Automation (UIA). Firefox already implements this translation and IE 8 has announced support for ARIA to UIA translation.
3. UIA: As mentioned above, UIA is the new accessibility framework for Windows applications that replaces Microsoft active accessibility. It provides a managed interface for accessibility while MSAA was just Com. UIA also simplifies the use of automation across multiple UI frameworks.
4. Assistive applications like screen readers: These are the clients ofapplications that expose accessibility related information through UIA and help people with disabilities use those applications.