A barista is somewhat comparable to both the sommelier and the mixer. A mixer works predominantly behind the bar counter, his job is mixing drinks, he is in immediate contact with the guests. A sommelier knows the origin of wines, the different procedures and the relationship of certain meals to certain wines.
The work area of a barista is more similar to that of a mixer, while the knowledge of the substances a barista must possess, is more like that of a sommelier. A barista is a little bit of an engineer as well, as occasionally he needs to control more than one grinders and coffee machines. Besides, the marketing of the product itself is often the job of the barista.