The system that we made tracks items that are stored in a specific warehouse.
These items are stored in specific storage areas(units). 

When an item is sold the quantity of that specific item is deducted,
and when an item is bought from the supplier the quantity of that item increases.

One staff manages storage of an item when it is bought from the supplier,
and one staff handles the sale of an item.

Products are categorized in order to improve querying and display of similar data.

The user can add inventory after making a category to add that specific item. 
Then all the data that the user requests is displayed in a table and the user can delete or edited

There is only one user (view) on the system

the data requirements we have used was based on our knowledge,
common sense and from google.....
So the logical and conceptual design we did was based on our discussion
that we thought was useful and important for an Inventory management System.