1. read a book, cannot really understand the following sentence:
"Data types vary from one RDBMS to another, so a user might need to use metadata to establish the data types used by a particular database."

Is that mean there is a metadata which is portable from one RDBMS to another?

2. using powerdesigner, confused by its int, integer, int(%n) and integer(%n). and also other tools use all upper case data type. ?????

Is that an exact quote? It doesn't make much sense to me...

If you need to compare the datatypes between two RDBMSs then consult the documentation. Unless the author meant databases not RDBMSs....

Yes. I copied.

PowerDesigner is a tool that manipulates more than one database engine (IBM DB2, Microsoft, MySQL, Oracle, Sybase, etc). Each engine implements different datatypes, and some of the engines have datatypes with the same name but different implementation specifics.

I suspect that the point that the author was trying to make is that the designer should not rely on any particular assumptions (is an INT 16, 32, or 64 bits long, is it signed or unsigned, etc). The long standing assumption among academic modelers is that the modeler is responsible for creating appropriate data types for each attribute (column), then mapping those custom types to what the implementation supports at the time the schema is implemented from the model.

-PatP