The Ice Cream Van of Abstraction

October 2020's T-SQL Tuesday is hosted by Rob Volk (b|t) with the subject Data Analogies, or: Explain Databases Like I’m Five! Thanks for hosting, Rob! It turns out that I don't do much specifically databasplaining™ by analogy, but there's one analogy I go back to again and again when talking to people unfamiliar with a useful concept, both inside and outside of SQL Server: abstraction.

We use abstraction all the time in computing, but a feature I'm frequently trying to communicate is that it introduces useful separation between a data consumer and the detail of how a data producer is implemented. A use case for this in an ETL environment could be isolating an SSIS package or a SQL stored procedure from an unexpected change to a source table structure – I've often used a SQL view to achieve this effect.

In this scenario, maybe your ETL batch crashes because a source table structure has changed and you weren't notified in advance 🙄. You're in a hurry to get back up and running, so you want to do as little work as possible to fix the problem. One approach is to create a view that selects data from the new table but outputs it in the old table format – change the data source from the table to the view and you're good to go. This isn't ideal, but it at least gives you some breathing room to make a fuller or more considered ETL pipeline reimplementation.

The reason this works is that the data consumer doesn't need to care about where data “really” comes from – table or view – as long as it presents the same schema¹⁾. This is the abstraction I'm trying to explain.

For anyone who's forgotten how an ice cream van works (it is October, after all), here's a quick refresher:

1. Ice cream van pulls up
2. You head over to the window, give the vendor some money
3. Vendor gives you an ice cream!

I like this analogy for abstraction because the rules are so simple – I hand over some money, I get an ice cream. The key is that I don't have to care where the ice cream comes from:

• maybe the vendor uses a machine to dispense ice cream into a cone
• maybe they pull one ready-made from the freezer
• maybe they run out to the van next door, collect a dispensed/ready-made ice cream and return it to me
• maybe they make and freeze a batch of fresh ice cream from scratch (OK, so I'd probably notice a delay here, but you get the point…)

If you're looking for a vehicle to explain why abstraction means you don't have to care about implementation, I offer you The Ice Cream Van of Abstraction!