Open Data

Open data is data that anyone is free to access, use, modify, and share, subject at most to conditions that preserve provenance and openness, such as attribution and share-alike. That wording follows the Open Definition maintained by the Open Knowledge Foundation. What makes data open is the combination the Open Definition sets out: a rights status of public domain or open licence, access to the whole work at no more than a reasonable one-time cost, machine readability, and an open format. Being visible or downloadable is not enough, and a licence alone is not enough either.

Three properties, and the one people forget

The Open Data Handbook describes open data through availability and access, the whole dataset at no more than a reasonable reproduction cost and preferably downloadable; reuse and redistribution, under terms that allow it, including combining with other data; and universal participation, with no discrimination against persons, groups, or fields of endeavour. A public web page with no stated terms has an unknown rights status; viewing is not a licence to copy, so the data is not shown to be open until the rights are checked. A free download whose terms allow only non-commercial use fails the third.

A fictional bus operator’s routes, stops, and timetables published under an attribution licence are open data. The same operator’s per-card trip records shared with one university under an agreement are not; that is controlled sharing, however useful it is.

What openness does not decide

An open licence answers who may reuse the data. It does not answer whether the data should be released at all, whether people can be re-identified from it, or whether the release matches what they were told. The Open Data Handbook notes that open data is concerned with non-personal data. Publishing personal records under an open licence does not make the release acceptable; it makes it irreversible, because downloaded copies cannot be recalled.

Openness is also different from interoperability, the ability of systems to exchange data and use it, which matters inside closed arrangements too. And open data still needs maintenance: documented field meanings, versions, a contact, and someone responsible for keeping it current.

References: Open Definition 2.1, Open Data Handbook: What is open data?. Examples here are illustrative.