加载位于symfony项目外的php类

I am building a frontend symfony app for a project with the current folder structure:

+---app
|   +---conf
|   +---lib
|   |   +---ca
|   |   |   +---Search
+---frontend
|   +---app
|   +---bin
|   +---src
|   |   \---PublicBundle
|   |       +---Controller

The app folder on root is where another (non symfony app) is located. It is a php app.

Inside the frontend folder is where symfony project is being built.

I am trying to load from inside the symfony app (from the public controller) a class from the other php app (a class inside the ca subfolder) but when I try to, symfony returns a namespace exception with the tip: Did you forget a "use" statement for another namespace?

It is correct to load a class from outside a symfony project like is, and if it is how is it done?

Thanks in advance,