How is HasURI attribute value assigned to centrasite assets

Hi,

When i do a metadata publish from designer the has URI value which is generated appears like
*hasURI:
uri://is/f89c7b76-7056-4533-8e0a-a54232386ddd/ns/.package/Default

can any one say how this "f89c7b76-7056-4533-8e0a-a54232386ddd"is generated? Does it represent any unique id that centrasite maintains in its DB?

And what is the purpose of this?

Thanks
Anusha Srinivasan