SDK architecture:CoreFileProperty Part is incomplete?

1) no strong-typed CoreProperty Class defined for the part's RootElement
2) no property for accessing the coreProperty node
3) the Package.AddCoreFilePropertyPart() method doesn't really allow you to create a valid usable CoreFilePropertyPart, it adds the file as well as the relationship,but thereafter,you find no way to add a rootElement... i've tried to write the core.xml extracted from a new word document to this part's stream, and i found the Code can read the Package.PackageProperties successfully,with every property recognized as 'null' no matter what's filled in the fields among the xml, and then i met the problem that i could not save the package by receiving a reception 'inconsistent compression length' or so ...

don't know what's wrong ,does it mean there is no way to construct a new CoreFileProperty with the SDK?

I think you create a CoreFileProperties part when you create your master document (e.g. PresentationDocument)
You can then access the CoreFileProperties by using a method:
CoreFilePropertiesPart Gets the CoreFilePropertiesPart of the PresentationDocument

Without a main document you wouldn't want a CFP - and creating a main document also create a CFP.

I haven't tried creating a CFP on it's own - but then I've never needed to.

I've also never needed to add a Core Property.