Inventory and it's Function

Inventory known as saved material in warehouse to used or sold next time (period). Inventory can be as raw material, material in process, and as a product which is saved to sold. Material is main subject as the right function for production project.
Inventory of raw material saved to process making a product. The existing of inventory of raw material is for managing total of raw material that will be used in production process.
The production process needs several times, where is the inventory's element is raw material.