What is Open Data?

Although the term "Open Data" seems intuitive and self-explanatory, there is no single universally agreed-upon definition. In most cases the domain and field of application guides the definition. One can get a feeling for this when looking at the various definitions for Open Data that we compiled here.

Though, in our daily work with data, we see two aspects regularly emerging:

• Legal Openness
  Can I legally use and reuse this data?
• Technical Openness
  Can I actually access and use the data easily?

Since our work spans many fields, we needed a consistent approach that works independent of any domain-based definition. This led us to develop ODON's Data Maturity Model (ODMM).

The ODMM assesses datasets along two dimensions — Legal Openness and Technical Openness — each with four levels, providing a clear, domain-independent classification.

ODON's Data Maturity Model (ODMM)

The framework assesses data along two independent dimensions: Legal Openness and Technical Openness. Each dimension has four levels. A dataset is assigned the level whose indicators all apply — or, for the first level of each dimension, the level that applies when any restriction is present.

Legal Openness

Level	Definition	Indicators	Classification rule
L1 Closed / Undefined	No clear legal permission for reuse	No explicit license is provided Terms of use are missing or unclear Default copyright applies	If any restriction is present → L1
L2 Restricted	License exists but limits reuse significantly	A license is explicitly provided License is publicly accessible License contains restrictive clauses (e.g. no commercial use, no derivatives, usage limited to specific groups or purposes)	All indicators must apply
L3 Open with Conditions	Reusable with minimal obligations	License is clearly stated and accessible Allows commercial use and modification Only light obligations (e.g. attribution, share-alike)	All indicators must apply Typical licenses: attribution-style licenses
L4 Fully Open	No legal barriers	Explicit open license or public domain dedication Allows commercial use, modification, and redistribution No mandatory obligations (or only trivial ones)	All indicators must apply Typical licenses: public domain / CC0-like

Technical Openness

Level	Definition	Indicators	Classification rule
T1 Not Usable	Data cannot be effectively reused	Not machine-readable (e.g. scanned PDF, image) No structured format Cannot be extracted without significant effort	If any restriction is present → T1
T2 Accessible but Limited	Technically accessible, but with barriers	Machine-readable format exists Data can be downloaded or accessed One or more limitations: proprietary format (e.g. XLSX only), poor structure (merged cells, inconsistent schema), or no metadata / documentation	All indicators must apply
T3 Structured & Standardized	Data is well-structured and usable	Non-proprietary, structured format (CSV, JSON, XML) Consistent schema and data structure Consistent encoding and formats Basic metadata available (field descriptions, update frequency)	All indicators must apply
T4 Fully Open & Interoperable	Data is optimized for reuse and integration	Meets all T3 requirements Uses open standards (e.g. standard vocabularies, formats) Stable identifiers (IDs, URIs) Versioning or update tracking available Available via API and/or bulk download	All indicators must apply

List of Definitions and Sources

Here you can find some of the definitions that exist on Open Data. For your convenience, we added also the source.

Source	Definition
Open Knowledge Foundation Open Definition	"Open data and open content can be freely used, modified, and shared by anyone for any purpose."
European Commission data.europa.eu	"Open data is data that anyone can access, use or share. Open data must be available online in an open format, accompanied by an open licence that allows the data to be re-used freely by anyone for any purpose."
World Bank	"Open data refers to data that can be freely used, re-used and redistributed by anyone – subject only, at most, to the requirement to attribute and share alike."
OECD	"Open government data refers to data produced or commissioned by government or government-controlled entities which can be freely used, reused and redistributed by anyone."
Open Data Handbook (OKF)	"Open data is data that can be freely used, re-used and redistributed by anyone – subject only, at most, to the requirement to attribute and share alike."
International Open Data Charter	"Digital data that is made available with the technical and legal characteristics necessary for it to be freely used, reused, and redistributed by anyone, anytime, anywhere."
Wikipedia	"Open data is data that is openly accessible, exploitable, editable and shared by anyone for any purpose, even commercially."

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