What is the name of the process & the responsible person to define the project structure?
Well many companies have a position called a solutions architect which is usually the one that is responsible for how the project is organized. In smaller companies, usually it is built through a consensus of developers, tech leads, project managers, stakeholders and those who usually work with the project on a daily basis. Each company does it a slightly bit different. Some leave it purely to the tech team as long as they can deliver on deliverables while others want to make sure everyone has a say. The main goal is that everyone on the project understands its organization, conventions and what is expected of them for standards. Usually this is outlined in some kind of scope document that is put together before the project even starts. Again, developed with input from several different sources. Edit: Many of the companies I have worked for typically put together a series of discovery meetings where the project sponsor (usually some executive) proposes what they would like to achieve and technical people fill in the details of how that can be accomplished and agree on how to proceed.