Open data is data that can be freely used and reused by anyone in new and unanticipated ways — subject only to minimal requirements such as attribution. There are a few key principles behind open data:
Permissive licensing — to enable use, reuse, and redistribution, data must be provided under terms that enable third parties to reuse data, including intermixing with other data sets, with minimal or no legal or policy constraints. There should be no restrictions against specific fields or groups of users (e.g., “non-commercial” or “education-only”).
Data availability and accessibility — data must be readily available, such as by download over the Internet. Data also needs to be in a convenient and modifiable format that enables reuse by programmers who may develop new applications. Typically, this is a machine readable format such as structured XML or equivalent.
Data discoverability — it is important that data be findable. Open Data relies extensively on some form of metadata to catalogue the data.