It has as its source a corpus, a database containing millions of examples of English as used around the world.

The award-winning Macmillan English Dictionary was first published in 2002. Crafted by teams of lexicographers in Britain and the United States, it has as its source a corpus, a database containing millions of examples of English as used around the world.
http://www.macmillandictionary.com/about.html

Is as used for referring to what someone or something does or how they appear?
Examples:
As managing director, I am expected to provide effective leadership.
a portrait of the princess as a child
An electric drill can also be used as a screwdriver.

Is as used for saying that something happens or is done in the same way?
Examples:
I invested the money as you suggested.
Leave everything just as you found it.