Question

I’d like to use an open source software that is licensed under Microsoft Reciprocal License (MS-RL)

Am I correct to think that I can use the open-source software for commercial purposes as long as:

1. Source Code (.dll) is provided with the distribution of my application. The dll will be dynamically linked.

2. MS-RL copyright information is written in the documentation I am providing

These copyright notices need to be written in plain english…

Answer 1

Microsoft Reciprocal License (MS-RL) is – as the name might suggests – a reciprocal license. This is the most common type in Free Software licenses (then those are often called copyleft type of licenses) as well as with indvidual, commercial licensing (most copyright materials are reciprocally licensed, e.g. the DVD you buy in a store).

That means, you need to keep the license not only for some part you use “in” your software package (e.g. the .dll if I understood you right), but also for the rest of the package. That is the general concept of reciprocity.

There is one exception in the license text itself:

You may license other files that are entirely your own work and do not contain code from the software under any terms you choose.

So if something is entirely your own work the reciprocity of the license won’t go over to your works in the package you distribute (if those works of yours are entirely your own).

What constitutes a non-derivative work (which is just another description of a work that is entirely your own) is defined by US-Copyright law for the MS-RL license.

As US-Copyright law is case-based there is nothing written inside the legal code that would be helpful for you here. E.g. whether you statically or dynamically link on it’s own does not say anything about the whether or not you have a non-derivative work.

Instead you need to contact a lawyer on your behalf that is going to review your software in sepcific and then look for existing cases, deciphers them and applies the legal code so that she could tell you whether or not providing source-code for your software is necessary or not.

As opposite to the GPL which has a strong community and discussion on international scale with both hackers and lawyers, the MS-RL license is not that widespread by far. So there is no common knowledge what is accepted or not on a practical level. Also there are not that many legal cases I’d say to get some useful information from.

If you can not afford the lawyer, I’d say the most easiest thing is that you accept the reciprocity of the license and release your software under MS-RL as well or (if an option) you stop using the component that is licensed under MS-RL.

Additionally you can contact the original author of that DLL and ask for clarification (e.g. if it is okay to use her/his software the way you do). If she/he writes yes, then you have a license your own next to what the MS-RL gives you. But you need to contact the copyright holder(s) for that.