2 Intermission: The anti-Hamlet

This is a real story about how negative numbers can cause severe economic loss. It’s based on a case we worked on with a client, but to be able to share the details, we’ve obfuscated the context. Most importantly, we’ve changed what the business sold. We can assure you that it wasn’t books. Interestingly enough, there are other examples that actually did involve books. Amazon had a similar bug around the year 2000.¹  But for those cases, we don’t know the under-the-hood details.

¹ Described, for example, in Gojko Adzic’s book Humans vs Computers (Neuri Consulting Llp, 2017).

This is also a story about how a serious security problem persisted in production for a long time without being detected and without anything being broken—at least, not in the technical sense. Nevertheless, it still caused money to bleed from the enterprise. Although the company could have uncovered who benefited unfairly, for practical reasons it wasn’t possible for it to recoup its losses.

2.1 An online bookstore with business integrity issues

2.1.1 The inner workings of the accounts receivable ledger

2.1.2 How the inventory system tracks books in the store

2.1.3 Shipping anti-books

2.1.4 Systems living the same lie

2.1.5 A do-it-yourself discount voucher

2.2 Shallow modeling

2.2.1 How shallow models emerge

2.2.2 The dangers of implicit concepts

2.3 Deep modeling

2.3.1 How deep models emerge

2.3.2 Make the implicit explicit

Summary