About project name and main item name

The so-called "engineering" refers to the way humans build products (physical or non-physical) that are larger and more complex than a single product. These products are no longer things with a single structure or function, but a variety of so-called "artificial systems" (such as: buildings, ships, airplanes, ideologies, etc.). “"Engineering" can be divided into broad and narrow senses. In a narrow sense, engineering is defined as "based on a certain set of conceived goals, applying relevant scientific knowledge and technical means, and through the organized activities of a group of people, the process of transforming some (or some) existing entities (natural or artificial) into artificial products with expected use value", such as: Yangtze River Three Gorges Project, Shenzhou 7 Project, wall decoration projects, etc. In a broad sense, engineering is defined as a process in which a group of people perform collaborative activities over a long period of time to achieve a certain purpose. Such as "211 Project (i.e.: "100 key universities for construction in the 21st century", "863 Project", etc. Simply put, a project can be large or small, physical or non-physical, and the brief description that makes up a "project" is the "project name". The so-called "main item" usually refers to an engineering entity that can have complete independent functions in the project, such as: A large-scale chemical project consists of installation engineering, public auxiliary engineering, environmental protection facilities, general plan vertical, off-site supporting engineering, etc. The above-mentioned engineering is composed of:: Devices, circulating water, substations, environmental monitoring stations, tank farms, roads... are all called "main projects", and the description that reflects the function of the "main project" is called the "main project name". However, this question post is really... and it has wasted a lot of my time. I hope to improve my posting skills.

The main items are mostly divided from the design perspective, but in project construction management, unit projects need to be re-divided. Can the division of unit projects directly follow the division of main items?

A unit project is a sub-project divided according to different types of work in a single project. In general, the main project uses the name of the most important unit project. For example, the main project of the natural gas pipeline project is the welding project, and the main project of the housing project is the civil engineering project.

Literally understood, the main item is just an item. The project should be a combination of many items, right? I don’t know, right?