[Content Suggestion] Clarify what is included in FOCUS "Amortization"

[AWS-ZachErdman]

Description

The FOCUS spec often refers to Amortization in a number of places and each time it provides a description of what Amortization is, but the exact definition has felt ambiguous to readers I've spoken with. Some examples of where Amortization is described:

First, a short line from FOCUS spec section “2.18.3 Description”:

"relevant purchases (one-time or recurring) paid to cover future eligible charges".

Second, a description from “2.18.3.2 Concerning Amortization Approaches”:

Eligible purchases should be amortized using a methodology determined by the provider that reflects the needs of their customer base and is proportional with the Pricing Quantity and the time granularity of the row.

Third, a longer description from “3.4 Discount Handling”:

Amortization is a process used to break down and spread purchase costs over a period of time or term of use. When a purchase is applicable to resources, like commitment-based discounts, the amortized cost of a resource takes the initial payment and term into account and distributes it out based on the resource's usage, attributing the prorated cost for each unit of billing. Amortization enables users of billing data to distribute purchase charges to the appropriate audience in support of cost allocation efforts. Discount Handling for purchased commitments is commonly used for scenarios like calculating utilization and implementing chargeback for the purchase amount.

While providers may use different terms to describe discounts, FOCUS identifies a discount as being a reduced price applied directly to a row. Any price or cost reductions that are awarded after the fact are identified as a "Credit" Charge Subcategory. One example might be when a provider offers a reduced rate after passing a certain threshold of usage or spend.

Proposed approach

We propose that the FOCUS spec provide an explicit and clear definition of what Amortization should include. Based on the text above, the definition could be something like:

"Amortization applies only to "Purchases" that are made solely for the purpose of covering future charges, as opposed to current charges.

Any rate reductions that occur from reaching a certain usage threshold (pricing tiering) would affect the usage where it begins and are NOT included in Amortization. Any cost reductions that would affect previous charges due to hitting a certain spend or usage should be issue as credits and are NOT included in Amortization."

Github issue or Reference

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Context

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