Replying to this , to answer if anyone still has this question .
Data types define and hold data for your application. For example, a Courses data type might be used to manage Course information. It might include the Department , description , hours , and so on. Data types are managed using the Data Explorer.
A data page is used to cache data on demand to a clipboard page for use by one or more applications. A data page rule defines the source, scope, refresh strategy, editability, and structure of the cached data. Data pages were previously known as declare pages. Data page starts with D_