PHILADELPHIA (CBS) — Big data is paying off for Philadelphia. The Revenue Department testified at city council budget hearings, Tuesday, that it found $4 million for the school district with a newly-completed “data warehouse” that gives it access to large amounts of information.

The money comes from increased collections of the little-known “School Income Tax,” on unearned income, such as dividends.

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The city had no real way to know if someone owed the tax. But revenue commissioner Frank Breslin says the data warehouse gives the city access to federal tax returns, which have unearned income as a separate line item.

“We were able to match that up and send them notices telling them that they owe the tax,” he said.

Breslin says the potential is huge, and not just for income information. The warehouse will connect city government, improving oversight.

“A contractor is interacting with L&I and pulling permits and licenses, well, are they also paying taxes to the city,” he said.

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City Council President Darrell Clarke seemed less than impressed. He’s been at odds with the revenue department over the process of selling tax delinquent property.

He says he asked no questions, but says he is saving them up for a separate hearing, investigating the department.