Definitions for open



This thread considers how open and public differ as concepts and provides several widely‑used definitions for “open”. Questions like these often surface during discussions on the advantages of open in its various contexts: open source, open data, open access, open content, and open science.

The concept of public simply means the content is made generally available to anyone. These days that can include publication on a website, download as a standalone file, or clonable from a code hosting site. Copyright normally attaches and the author retains all rights by default, even if no explicit claim is made. All rights reserved copyright is debilitating for open science for reasons covered later.

In operational terms, open means that the content carries a suitable open license. Open licenses grant recipients permission to use and modify the material and republish any changes that they might make under the same or compatible terms. This last point is the key — such re‑use allows improvements to be returned to the information commons for all to benefit. Unlike proprietary licenses, open licenses grant these permissions to anyone who complies with the stated conditions — without the need to negotiate with rights holders on an individual basis.

Widely‑accepted definitions for open apply to each category of content: software, data, academic publishing, and other forms of content. These are listed below. Each category has different legal considerations, different definitions, and therefore different sets of licenses. For instance, software licenses should address software patents whereas licenses suitable for data need not.


The term software covers both source code and object code, with the latter including executable programs. The gold standard definition for open software is the Open Source Initiative (OSI) Open Source Definition (OSD):

In addition, the OSI act as a license steward and maintain a list of approved licenses. The Free Software Foundation (FSF) also publish an operationally equivalent definition to the OSD, widely referred to as the “four freedoms”.

As indicated, software licenses need to consider legal issues specific to software and only explicit software licenses should be applied to source code.


Like software, data requires specific legal considerations, including the question of database protection for collections of facts and values served from within Europe. The gold standard definition for open data is the Open Knowledge International (OKI) Open Definition:

Creative Commons licenses before version 4.0 do not specifically traverse database rights and similar issues and should not be applied to datasets and databases.

Academic publishing

Open access publishing attracts a range of definitions, starting with the mere absence of a paywall. But to be generally useful, open access should allow for the re‑use of content. The gold standard definition for open access is the Berlin Declaration:

Note that the phrase in the declaration “for any responsible purpose” is advisory only under German law and is therefore not legally binding in that jurisdiction at least.

Other forms of content

Other forms of content more generally should be published under conditions that meet the OKI Open Definition (see above).


The concept of open is additional to the concept of public. The concept of public results simply from the act of publishing, that is, of making the material available to the public at some cost or free of charge. If no open license is provided, full copyright is typically retained plus other relevant protections such as European database rights.

Of the several categories of open content listed above, it is open data which provides the most problems for open energy system modelers. That is why there has been a broad effort to get public sector information providers to add either Creative Commons CC‑BY‑4.0 licenses or CC0‑1.0 public domain dedications at their discretion.

In terms to conception, it is useful to distinguish between an open work and a open license. An open work remains the primary objective and a particular open license is simply the legal vehicle to articulate the binding conditions and ascribed rights under which the open work exists. For instance, defines open source in terms of “open exchange, collaborative participation, rapid prototyping, transparency, meritocracy, and community‑oriented development” without explicitly mentioning intellectual property rights or licensing. Likewise, the OSD for software does not mention specific intellectual property rights either. In a similar spirit, the Open Definition defines the characteristics of an open work and an open license.

Choice of license issues are not traversed here. Selecting a suitable license is a complicated subject, refer instead to the references below. The purpose of this thread is to list the gold standard definitions for each category of content for general reference.

Content without an open license is highly debilitating for open science. Source code without an open license cannot be lawfully built or run. Data without an open license cannot be modified and republished, at least not with legal certainty. Academic publications which languish behind paywalls hinder the dispersion of knowledge. And academic publications without an open license prevent both text and interpreted data from being generally used and republished.

Further reading

Ball, Alex (17 July 2014). How to license research data. Edinburgh, United Kingdom: Digital Curation Centre (DCC).

Hirth, Lion, Ingmar Schlecht, and Jonathan Mühlenpfordt (6 November 2018). Open data for electricity modeling: an assessment of input data for modeling the European electricity system regarding legal and technical usability — White paper. Berlin, Germany: Neon Neue Energieökonomik. A report for the Federal Ministry for Economic Affairs and Energy, Germany.

Lämmerhirt, Danny (December 2017). Avoiding data use silos: how governments can simplify the open licensing landscape. Open Knowledge International. Cambridge, United Kingdom.

Meeker, Heather (4 April 2017). Open (source) for business: a practical guide to open source software licensing (2nd edition). North Charleston, South Carolina, USA: CreateSpace Independent Publishing Platform. ISBN 978-154473764-5.

Morrison, Robbie, Tom Brown, and Matteo De Felice (10 December 2017). Submission on the re-use of public sector information: with an emphasis on energy system datasets — Release 09. Berlin, Germany. Published under a Creative Commons CC BY 4.0 license.

Opensource (no date). What is open source?.

Open modeling/environmental NGO bridge

Another open definition (see reference below), this from the OpenForum Europe (OFE), focuses on technology interoperability. Interoperability is also a consideration for energy system modelers in light of growing interest in energy sector digitalization, smart grids, and smart consumption. The Linux Foundation LF Energy initiative also represents a step in this direction, in which open (and royalty free, one would hope) interface standards and open implementations of same are central. (My thanks to OFE for the pointer.)


OFE (no date). Our vision — the OFE openness principles. OpenForum Europe (OFE). United Kingdom.

LF Energy — Open Source for Energy Transition. LF Energy. Website.