If you've got some experience building Integration Services packages, you probably already know that SSIS has its own representation of different data types. The names of these data types start with DT_, followed by the data type such as I for Integer, BOOL for Boolean, STR for String, and so on.
Each time we move data from a source to a destination, conversion between input and output data types is required. The following figure shows a list of the most used data types and their relationship between different environments.
To get further details about SSIS data types , refer to the Working with Data Types in the Data Flow topic in Microsoft SQL books online at the following URL:
http://msdn.microsoft.com/en-us/library/ms345165(v=SQL.110).aspx.