professional diploma

For the sake of convenience please allow me to answer in English.

First of all, Level-4 (Qualification Framework) refers to the level of a higher diploma, not a bachelor's degree (which is Level-5). So the Professional Diploma you mentioned is not up to a Bachelor's degree level.

Professional diploma is not a formal qualification in the academic structure. You can see it as a short course in a specific topic area (at higher diploma level in your case), or an <endorsement course> in technical education in the era of 60s.

It addresses the need of people who have no time or intention to complete a full course but look for some short term study in a specific study area which he/she finds interesting. In other words, just pick the interesting part of a degree/HD course. It is also suitable to people who have got a bachelor's degree or a higher diploma, and wish to learn more in other specialisms.

Based on the philosophy of credit-unit system, it is possible that by completing a number of parallel professional diplomas, the offering institution might issue you a collective award (a full higher diploma, for example). Quoting an example of the Open University of HK, there are quite a number of post-graduate diplomas offered in the field of education. Students who have completed a sufficient number of these post-graduate diplomas will be awaded a collective award - the MEd.

A professional diploma may or may not be recognised for exemption from a bachelor's degree curriculum. It depends on the prevailing academic standing of the qualification.