GlobalData Has to do Something With The Component or Custom Controller Level Which is Used when u have to interact with two or More Views.
Whereas Model Data has to do with Businees Logic where the program interacts with ur Database level and inserts or updates or delete the data u send to the back end.
The Model Data can be any thing, It can be ur SAP FunctionModules, Enterprse Java Beans , Webservices etc..
The term Model is used to describe the layer that grants a framework like Web Dynpro access to the
business logic, may the business logic reside in a backend like R/3 for instance or may it be
implemented in Enterprise Beans, based on JDO or whatever. A Model has to expose business
data and metadata (at least via reflection) via the Common Model Interface to the framework that
sits on top of the CMI.