# Inventory Approaches

OSCAL makes two approaches available for depicting the system inventory:

- **Flat Approach**: Aligns with today's FedRAMP Integrated inventory workbook where all of the information on a spreadsheet row is captured in a single assembly. 

- **Normalized Approach**: Common information is normalized as OSCAL components. inventory-items point to components for common information. 


With the **flat approach**, all content on a spreadsheet row appears in a single OSCAL inventory-item assembly. This results in a great deal of redundant information but is a simple transition from the current spreadsheet approach.

See [Inventory: Flat Approach](https://patterns.rufrisk.com/books/fedramp-system-security-plan-ssp/page/inventory-flat-approach) for more information.

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### Retrofit Adoption Path: MVP

If you have an existing FedRAMP authorization and are using the FedRAMP inventory spreadsheet template, start with the flat approach, and migrate over time to the normalized approach.

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With the **Normalized approach**, common information is captured once in a component assembly. Each instance of that component has its own inventory-item assembly, which cites the relevant component and only includes information unique to that instance.

See [Inventory: Normalized Approach](https://patterns.rufrisk.com/books/fedramp-system-security-plan-ssp/page/inventory-normalized-approach) for more information.

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### New Adoption Path: Core

If you are adopting OSCAL at the beginning of your FedRAMP journey, define components first, then regerence those components as you generate inventory.

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#### Example

The same Linux operating system is used as the platform for all database and web servers. Most details about operating system are captured once as a component, including OS name, version number, and patch level. 

If four Linux instances are used, each instance is an inventory item with a unique IP address and MAC address. Only those unique pieces are captured at the inventory level. All four inventory-items are linked to the component.