I was going to explain to you about the separate Gothic origins for "while" and "as", but after I saw that your web site is giving English consultation, I think that I will only advise you to research more in your field of expertise.
I see that you are from Monterrey, Mexico. In your native language, which should be Spanish, you should note that "mientras" normally corresponds to "while" while "como" corresponds to "like" or "as". At first, I thought that you were asking about the differences between the latter of your aforementioned terms. Logically, with both English and Spanish having lucidly differing sematic usages between "while" and "as", I am surprised to find you asking this question.
What I find absurd about your entry is that an English training service would ask for advice about their suppossed specialization.
Mientras tanto, disfrute de la vista del Cerro de la Silla.
Eric Paul Monroe