This document discusses event sourcing, which is a technique inspired by double-entry bookkeeping that records all changes to data as a time-ordered sequence of events. It provides an example of tracking inventory levels of tuna sushi using event sourcing by recording purchase and sale events, and shows how the current inventory level can be calculated on demand by replaying the sequence of events from the beginning. The key advantages mentioned are that event sourcing stores all changes chronologically without snapshots and allows reconstructing any point in time by replaying prior events.

1. EVENT SOURCING
2017-10-28
@takesection

2. I AM SHIGEKI SHOJI

3. Ideas from Double-Entry Bookkeeping

4. Event
Event
Event
λ
Save in time series
λOn demand view

5. DOUBLE-ENTRY SYSTEM
EVENT NO DEBIT CREDIT
1 Tuna Sushi - 10 pierce Account Payable - 30 pt
2 Cash - 50 pt Tuna Sushi - 5 pierce
3 Cash - 30 pt Tuna Sushi - 3 pierce
4 Tuna Sushi - 10 pierce Account Payable - 30 pt

6. CALCULATION OF INVENTORY
QUANTITY

7. THERE IS NO SNAPSHOT
Start from the creation of heaven and earth.
1 +10 10
2 -5 5
3 -3 2
4 +10 12
Tuna Sushi - 12 pierce

8. DR CR
Sum 20 8
Tuna Sushi - 12 pierce 20 - 8 = 12

9. USAGE SNAPSHOT

10. Event
Event
Event
λ
Save in time series
SNAPSHOTS
λOn demand view

11. NO DR SUM CR SUM
4 20 8
(20 + 10) - (8 + 13) = 30 - 21 = 9 pierce

12. THANKYOU!
https://github.com/takesection