[olsgaarddk]

At the tax authority we could query that directly from a database.

But yes, the public sector suffers from countless different systems that have accumulated over the years. It happens because everything has to go out to a public bid and throughout the times it has been considered anti competitive to built things in-house.

[TeMPOraL]

More than that, the vendor winning the bid will happily use the opportunity to latch itself to the flow of taxpayer money. That's a big reason you end up with XML hell - the systems are designed to make future interop impossible without going through the vendor.

In fact, wasn't Denmark a case study of that? I remember there was someone on HN a while ago, IIRC working in public service of some country in Europe, who posted stories about their constant fighting with a vendor who intentionally makes it very hard to have any kind of integration and data exchange between various administrative branches.