# Once Only Principle The [Once Only Principle](https://ec.europa.eu/cefdigital/wiki/display/CEFDIGITAL/Once+Only+Principle) is an e-government concept that aims to ensure that citizens, institutions, and companies only have to provide certain standard information to the authorities and administrations once. By incorporating data protection regulations and the explicit consent of the users, the public administration is allowed to re-use and exchange the data with each other. The once-only principle is part of the European Union's (EU) plans to further develop the Digital Single Market by reducing the administrative burden on citizens and businesses. * Public service customers (citizens, institutions, and companies) should not have to supply the same information more than once to public administrations. * **APIs should store collected data in a single database**. That means for example when a service is enriching existing data from another database it should store the enriched data in it's own database, with only a linkable identifier to the existing data. ## References * [Connecting Europe Facility](https://ec.europa.eu/cefdigital/wiki/display/CEFDIGITAL/Once+Only+Principle) * [Wikipedia](https://en.wikipedia.org/wiki/Once-only_principle) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.devland.is/technical-overview/api-design-guide/once-only.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.