What Is Open Data? — Open Data Handbook
Open data is about interoperability
If you’re wondering why it is so important to be clear about what open means and why this definition is used, there’s a simple answer: interoperability.
Interoperability denotes the ability of diverse systems and organizations to work together (inter-operate). In this case, it is the ability to interoperate - or intermix - different datasets.
Interoperability is important because it allows for different components to work together. This ability to componentize and to ‘plug together’ components is essential to building large, complex systems. Without interoperability this becomes near impossible — as evidenced in the most famous myth of the Tower of Babel where the (in)ability to communicate (to interoperate) resulted in the complete breakdown of the tower-building effort.
We face a similar situation with regard to data. The core of a “commons” of data (or code) is that one piece of “open” material contained therein can be freely intermixed with other “open” material. This interoperability is absolutely key to realizing the main practical benefits of “openness”: the dramatically enhanced ability to combine different datasets together and thereby to develop more and better products and services (these benefits are discussed in more detail in the section on ‘why’ open data).
Providing a clear definition of openness ensures that when you get two open datasets from two different sources, you will be able to combine them together, and it ensures that we avoid our own ‘tower of babel’: lots of datasets but little or no ability to combine them together into the larger systems where the real value lies.