Open standards and open source

Module 2: What is a European cloud, really? · Reading time: 11 minutes

Learning objective: After this lesson, you can explain the difference between an open standard and open source, and name the standard that makes switching easy for each part of your work (mail, calendar, contacts, files, documents).

Key terms: open standard, open source, licence (AGPL), RFC, IMAP, SMTP, CalDAV, CardDAV, WebDAV, iCalendar (ICS), vCard (VCF), ODF, OOXML, federation

Why standards give you freedom

Imagine every phone provider used a different type of plug. Switching would mean: a new charger, new cables, maybe a new phone. Cloud services work the same way. If a service uses agreements that anyone can use, you can take your data and your apps with you. If it uses its own proprietary agreements, you're stuck.

Bakkerij De Korrel wants to be able to choose now, and to choose again later. That's why it looks not only at who provides a service (lesson 2.1), but also at the "plugs": the standards the service speaks.

Open standard and open source: two different things

An open standard is a publicly documented agreement on how programs exchange or store data. Anyone may read and use it, without permission or payment. Many internet standards are laid down in an RFC (Request for Comments) from the IETF; document formats are often set as an ISO standard. An open standard says nothing about who makes the software.

Open source is about the software itself: the source code is public and under a licence that allows you to read, use, modify and distribute the code. Nextcloud, Thunderbird, LibreOffice and Euro-Office are open source.

They often go together, but not always:

For a switch, open standards matter most. They let you take your data with you, even if the software is closed. Open source is an extra safeguard: if a provider stops or changes course, someone else can keep running the same software.

The standards for each part

These are the agreements you'll keep encountering throughout the rest of the course.

Note the last block: docx is also a documented standard, not a secret format. In practice, Microsoft Office uses a variant with extras, and a document can come out looking slightly different in another program. Lessons 6.3 and 6.5 cover that.

How do you recognise a service built on standards?

You don't need to read any RFCs. Ask these questions:

1. Can I read my mail with any mail program via IMAP? If only the provider's own app works, that's a bad sign.
2. Can I link my calendar and contacts to my phone's calendar without an extra app from the provider? Then CalDAV and CardDAV are probably available.
3. Can I mount my files as a network drive? Then WebDAV is available.
4. Can I export a calendar as ICS and contacts as VCF? And can I import them?
5. Are documents stored as docx/xlsx/pptx or odt/ods/odp? Or in a proprietary format that only exists inside that service's browser?

A technical test is also possible. Many services publish a .well-known address: https://cloud.example.com/.well-known/caldav redirects a calendar app to the real calendar address. And the DNS can contain an SRV record, such as _caldavs._tcp.example.com or _imaps._tcp.example.com, which tells apps where to look. Exercise A2.2 checks this for your cloud address.

Federation: working together across the boundaries of a single service

Some open standards let services from different providers talk to each other. This is called federation. The best-known example is email: someone with a mailbox at provider A can email someone at provider B without any trouble. Nextcloud supports federated sharing: you share a folder with someone on a different Nextcloud server. For chat, Matrix is a federated standard. Federation makes it less risky to be with a smaller provider: you're not cut off from everyone else.

With closed platforms (a chat service that only works within that service), everyone you work with needs to be on the same service. That's a strong form of lock-in, which lesson 2.3 comes back to.

Open source: what it does and doesn't mean

Open source is not a safety mark, and not a mark of European ownership either. Three misunderstandings:

• "Open source is secure." Public code can be reviewed by anyone, and with large projects it is. But a poorly maintained project can contain just as many leaks. Look at maintenance: how often do updates appear, is there a security policy?
• "Open source is free." The licence costs nothing, but running, updating and securing it costs time or money. That's why many organisations choose a provider who manages the software for them.
• "Open source is European." Where the makers are based has nothing to do with the licence. What matters most is that you or another provider can keep running the software if the original maker changes something.

A commonly used licence in the cloud world is the AGPL (GNU Affero General Public License, version 3). It requires anyone who offers modified software as an online service to also make the modified source code available to users. Nextcloud and ONLYOFFICE use the AGPL. That the licence allows software to be split off (a fork) was seen in 2026: Euro-Office emerged as a fork of ONLYOFFICE. ONLYOFFICE believes licence terms were breached in the process and ended its cooperation with Nextcloud; no court ruling on that dispute is known as of November 2026. For this course, the key point is: an open licence makes such a fork possible, and that gives users a way out if they no longer trust a supplier. Who is right in this dispute is for lawyers to decide.

In practice: what it looks like with a provider

A WebOké Nextcloud uses WebDAV for files, CalDAV and CardDAV for calendar and contacts, and can import and export ICS and vCard. Euro-Office stores documents as docx, xlsx and pptx, and can also open odt, ods and odp. This means programs from other makers also work, such as Thunderbird, the calendar on your iPhone or DAVx5 on Android. With other providers running on the same standards, it works in a similar way: that's why you can move away again later too (lesson 8.2).

Summary

• An open standard is a public agreement about data; open source is about public source code. They often go together, but not always.
• For a switch, the standards matter most: IMAP and SMTP (mail), CalDAV and CardDAV (calendar, contacts), WebDAV (files), ICS and vCard (export), ODF and OOXML (documents).
• You recognise a service built on standards by IMAP access, linking to your phone's own calendar, WebDAV, and export in ICS, VCF and docx/odt.
• Federation lets services from different providers work together.
• Open source isn't automatically secure, free or European, but it does allow someone else to keep it running.

Quiz

Exercise

Exercise A2.2: Does your cloud speak open standards? Enter the address of your current or new cloud (for example cloud.example.com) and your mail domain. The program checks whether the .well-known addresses for calendar and contacts exist and whether there are SRV or autoconfig records for mail, and shows you what it found.

Further reading

The steps in these articles apply to WebOké's services; with other providers it works in a similar way.

• Nextcloud manual 1.5: Which browsers, apps and devices work?
• Euro-Office guide 1.4: Which browsers and file formats work with Euro-Office?
• Nextcloud manual 3.5: App passwords: when and how to use them
• DirectAdmin guide 8.7: IMAP or POP3: what's the difference?
• RFC 9051 (IMAP4rev2), RFC 5321 (SMTP), RFC 4918 (WebDAV), RFC 4791 (CalDAV), RFC 6352 (CardDAV), RFC 5545 (iCalendar), RFC 6350 (vCard 4.0), RFC 6764 (finding CalDAV/CardDAV), RFC 6186 (mail SRV); ISO/IEC 26300 (ODF), ISO/IEC 29500 (OOXML)