19. The volatile or non-volatile machine-readable storage medium of claim 16 , wherein the one or more sequences of instructions causes the one or more processors to perform converting the instance by: generating a logical representation for said object identifier that is recognized among the multiple sites, and incorporating said logical representation of said object identifier within said logical representation of said complex type.
16. A non-transitory volatile or non-volatile machine-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform: converting an instance of a complex type from (a) a first storage format within a first database used at a source site to store the instance of the complex type to (b) a logical representation that conforms to a markup language and is recognized among multiple sites; propagating said logical representation to at least one destination site; and at a destination site, converting said logical representation to a second storage format used to store instances of the complex type within a second database at the destination site, said second storage format different from said first storage format; wherein the instance of the complex type in the first storage format within the first database at the source site includes an object identifier that identifies at least part of the instance of the complex type at the source site, wherein the object identifier is tied to the source site and is not used to identify the at least part of the instance of the complex type in the second storage format within the second database at the destination site, and wherein the logical representation includes a globally unique identifier that is recognized among the multiple sites as representing the at least part of the instance of the complex type.