The Elephant in the Fridge by John Giles

Author:John Giles [John Giles]
Language: eng
Format: epub
Publisher: Technics Publications
Published: 2019-05-01T16:00:00+00:00

Alex and Chris, are salaried employees, managed in the Payroll system. Brook and Dan are contractors, managed in the Contract Management system. All four employees are also recorded in the central Human Resource (HR) system. In addition, Alex, Brook, and Dan have been issued with cards to get access to the head office building (Chris doesn’t need one for his/her line of work out in the field because he/she rarely if ever visits the head office).

In the diagram, we also have arrows. These denote one system’s knowledge about the business keys of another system. The first row, for Alex, indicates that the Building Access Control system obviously knows about its own keys, but also knows the Payroll system’s Employee Number for Alex.

In this hypothetical, the HR system generates its own employee numbers, which are the “business keys”, used and known by each employee as their identifier. They enter it on timesheets, and quote it if they ever have to record other activities. Yes, it is internally generated by the HR system, and some may argue it’s a surrogate, but it is externally visible, and it is used by the business as the identifier for employees.

The Payroll system also has employee numbers, but it doesn’t generate its own. It simply reuses the employee number as generated by the HR system.

The Contract Management system is a little different. When someone is added as a new contractor, the Contract Management System generates its own key which is issued to the contractor – it’s another business key! But what’s more, the Contract Management System also records the HR system’s employee number. Please note that while both systems use integer numbers for their keys, they are generated independently. As it turns out, the number “2” appears in both systems, but Employee Number 2 is for Brook (whose Contractor Number is 1), and Contractor Number 2 is for Dan (whose Employee Number is 4). Confused?

Finally, we’ve got the Building Access Control systems’ Card Holder Numbers. Again, these can be used as “business keys”, as they appear on the card itself, and can be recorded by people at the front office desk. Thankfully, these business keys are alphabetic, and cannot be confused with any of the other business keys for employees. Please note than when a card is issued (and its Card Holder ID generated), the system also records

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