I imagine most people would call doctors and lawyers upper middle class, but I would also say if you want to try and be technical about it, they are an older type - people who own their own small businesses.
Craftsmen, small farmers who own their own land, etc, have been around since before the industrial revolution and occupy a sort of unique place that is neither the proletariat class and the capitalist class. Generally they own their own means of production, which is not just their tools but also their skills and knowledge, and while they may have some employees they are not employing on a mass scale or even close to it, for the most part.
This is the group that the Distributists, like Hilaire Belloc, thought should form the backbone of society, rather than capitalists or the state in a state socialism model, which they say as two sides of the same coin (control by the elite.) The economy should, to be most fair and balanced, be dominated by small business owners who worked for themselves - who owned their own jobs.
Middle classes in large numbers are a newer thing and represent sellers of labour who have secured a lot of stability and support through being able to integrate themselves into the capitalist ownership framework, even if at a low level.
This gives them a lot of advantages, economically, generally, and in terms of security, compared to the historic working class who really were at the mercy of the capitalists who owned their jobs.