To this day, design has always been defined in a highly broad and abstract way.  Design is expressed in the most creative way, and it differs from paintings, sculptures and other perceptual artistic forms, as well as from other numeric descriptions of rational thinking including engineering drawing. On the other hand, design must be featured with rational analysis and perceptual expressive ability. Only the perfect combination of the two aspects can form a unique language of designers. Design is not to attract people's attention instantly through strong visual impact, but by slow infiltration. It has been entirely conveyed before any attention is paid.  This indicates that no matter how designers use visual languages in design, all of them are used to serve the practical value.