Product-specific certifications are generally more complex because they are intended to be referenced to a product across all applications.
This approach is very prevalent in the information technology (IT) industry, where personnel are certified on a version of software or hardware. This type of certification is portable across locations (for example, different corporations that use that software), but not across other products.
The most general type of certification is profession-wide. In order to apply professional standards, increase the level of practice, and possibly protect the public (though this is also the domain of licensure), a professional organisation might establish a certification. This is intended to be portable to all places a certificate might work. Of course, this generalisation increases the cost of such a program; the process to establish a legally defensible assessment of an entire profession is very extensive. An example of this is a certified public accountant, who would not be certified for just one corporation or one piece of accountancy software but for general work in the profession.