Owing to its interdisciplinary nature,quantitative biology is playing ever-increasing roles in biological researches.To make quantitative biology even more powerful,it is important to develop a holistic perspective by integrating information from multiple biological levels and by considering related biocomplexity simultaneously.Using complex diseases as an example,I show in this paper how their ontological connections can be revealed by considering the diseases on a common ground.The obtained insights may be useful to the prediction and treatment of the diseases.Although the example involves only with cancer and diabetes,the approaches are applicable to the study of other diseases,or even to other biological problems.