Legal Team/Templatizing

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This is the working area for the technical and legal teams. The focus of this effort is for recording ideas and considerations about improving machine detection and recognition of licenses and headers in code.


(from JL) The current Matching Guidelines and license markup was developed over the past several years. While the guidelines were relatively easier to come up with, how much markup to use and how to implement it was an on-going discussion of much debate. As relevant to the proposals here, the discussion around how much markup to use recognized that more markup would increase consistent results by reducing the need for tool makers to interpret the guidelines. However, due to the amount of work of potentially having markup on every license file, a more conservative approach was taken with the recognition that we could always add more markup over time (but taking it away would be harder).

The template language was a result of a collaboration between members of the legal and technical teams. The goal of the template was developed with the following goals in mind:

  • Enable both humans and, to a lesser extent, tools to be able to determine if two license texts were equivalent.
  • Preserve the original language of the license text.
  • Leverage existing annotations and tools (e.g. the use of regular expressions to denote matches to variable text).

The current templating language is documented in Appendix II of the specification (


(from Gary) As a result of the initial bug 1302 discussion, Gary suggested to enable pull requests to be made against the SPDX License List, which would encourage contributions to markup by others. Such pull requests/contributions would be moderated by the Legal team (especially regarding determinations of markup and potential impact on legal interpretation of the license) with help from the Tech team as needed. Everyone on the Aug 6 legal call agreed this would be a great approach. Gary, Jilayne, Kate have begun to discuss how to implement this. A process also needs to be outlined for how pull requests will be handled, etc. A rough draft process proposal can be found in the google document

(from Kris) Things that would improve working with the data programmatically:

  • Get away from spreadsheets as the index for the licenses. Use JSON or XML (leaning towards XML to keep the toolset the same as markup parsing). A tool to compile the spreadsheet (for humans to work with) down to an XML file would probably work.
  • Put all information about a license in the same place for each license (headers, addons/exceptions/whatever). Likely within markup within the license files themselves.
  • Use XML or some other widespread format for the markup. This ensures there are tools available to work with the data in any language without having to write custom parsing tools or use tools tied to a specific platform because they're the only ones that exist.
  • As, and if, the data moves towards a more markup-heavy format, it might be wise to simply include the full text verbatim in its own section rather than "recreate" it from marked up data.

An example of what a more normalized (to xml) data set might look like:


   <license identifier="Apache-2.0" file="Apache-2.0.xml">Apache License 2.0</license>


   <original>...full original text content...</original>
     <header>...Licensed under the Apache License, version 2.0, etc....</header>
     <body>Some text blah blah <match regex="foo|bar"/> more text</body>

An alternative:


The above carries the useful property that the text content of the body tag is the original source without any modification; processing can instead replace "alt" tag contents with their regex attribute to "convert" to a matchable format.

I don't actually like XML, but it seems to be a good fit for this purpose. It helps keep the intrusiveness of the markup into the license text focused and to a minimum, lets us wrap entire sections as optional, keep the canonical original text if desired, and specify alternate license formats such as the short-form license header and any desired metadata all in one place. And there are tools to read XML in every language.

I recommend that the template content be *without* the parts that the matching guidelines say to ignore, and preferably it should have normalized or marked up bullets, etc. Best of all would be, simply, normalized text content in a full regular expression that can be used to match directly, rather than a bunch of markup that must be turned into a regular expression -- but I think this would make maintenance much harder. Again, a compilation step could help. There's a lot of work to be done here that can be qualified as preprocessing, and there's no reason we can't make sure the preprocessing is "done right" and publish the results, instead of requiring programmers to reimplement their own version of the preprocessing with uncertain results.

A particular note about normalizing text: Bullet items are one of the problematic points for parsing because it can be troublesome to distinguish a bullet point like "ii." from the end of a sentence that got wrapped to the start of the next line. (I actually encountered this in my testing; a saving grace is that the bullets tend to be things that are hard to confuse for words, but it's really easy to write a regular expression that isn't that smart.)

For what it's worth, I'm quite happy to contribute when it comes to tooling; I already have code to do the most of this anyway. -Kris

Use and Feedback re: Current Markup

Feedback was solicited on the legal and tech mailing lists to this end:

We have a task to add markup to some of the standard headers and have also had input to add/edit markup on existing licenses. As a result of the latter, it has been raised that perhaps the markup could be improved. Before adding more markup (to standard headers, license text or both), it seemed prudent to start a discussion as to whether the existing markup is effective. Please ponder the following questions: a) have you used the existing markup for matching purposes? i) if no, why not? ii) if yes, has it been helpful/effective? Could it be improved, and if so, how? (this will likely involve putting forward a proposal for review)

Please record your input in a section here, by name or tool or both:


feedback was provided as follows:

Gary O'Neall

[G.O.] For the SourceAuditor commercial tools, the markup is used to validate that 2 licenses are equivalent per the matching guidelines. The open source SPDX tools uses the markup is used in a number of ways. The "compareSpdx" and "compareMultipleSpdx" commands use the markup to determine if the licenses are equivalent. There are library methods implemented to compare license text and report if the license text matches any of the SPDX LicenseList.

In all cases above, the markup is used to compare 2 existing known license text. It is NOT used to match license text against a library of possible license matches. In the commercial tool, a separate algorithm implements this functionality and the markup language turned out to be too inefficient for this purpose - at least for the performance requirements of our application.

Note: When we originally discussed the markup language, we debated whether to cover the use case of searching a library of possible license matches and the decision was taken not to support this.

In my opinion, the markup works fine for matching two license texts. If we wanted to support a searching use case, we would need to modify/extend the markup language to enable this to be efficient.

Performance would be greatly improved if we bounded the RE's. Something which is within the spec, but is not implemented in the templates. I would support implementing bounding all RE's in an upcoming release and changing the spec to encourage bounding. I think we could pick a pretty practical upper bound that would improve the performance.

Also note - this is more of an issue with the "matching against a library of licenses" issue than simply comparing two license texts since the former is more performance sensitive.

Sam Ellis

I will share a few points from my experience in templatization. I currently use a different templatization syntax that predates SPDX, but the principle of using regular expressions embedded within the license text is similar.

The major barrier to me adopting the SPDX templates is insufficient templatization within the existing licenses. The SPDX templates currently encode what I perceive to be the ‘official’ variations, i.e. organization name, person name, product name etc. However, real-world licenses contain may minor variations that may be inconsequential from a legal perspective, but nonetheless do not warrant separating out as separate licenses. Here is an example from the GPL-3.0 notice where it is common to see two variations in one of the sentences:

distributed in the hope that it will be useful distributed in the hope that they will be useful

The example above is fairly uncontroversial, I would hope. However, there are plenty of other examples that border on having a legal impact. For example, in these two BSD-2-Clause variations it is necessary to consider whether the additional word constitutes an acceptable minor variation or warrants a different classification altogether:

Redistributions of source code must retain the above copyright notice, this list of… Redistributions of source code must retain the above copyright notice unmodified, this list of…

It is the grey cases like these that make expanding the use of templating difficult. Inevitably it leads to having to make some judgements about the impact of a particular word or phrase on the legal interpretation, something that I am aware SPDX tries to avoid.

Whether it is worth templating all the cases like these primarily depends on the goals of the SPDX templates. If they are for human use to see what official variations are permitted, then they are not necessary. On the other hand, if they are to be used by automated license scanning tools, then covering these cases is essential in order to have a tool that works effectively on real-world code. So I think an important point is to gain clarity on the purpose of the templates.

In terms of the current application of the templates, I have a technical concern over the use of unbounded regular expressions, for example:

<<var;name=copyrightHolderAsIs;original=THE COPYRIGHT HOLDERS AND CONTRIBUTORS;match=.+>>

This is unbounded because it will match any number of characters for the copyrightHolderAsIs field. The practical consequence of this is that regular expression matching can explode in terms of time. I don’t have a concrete example to hand, but my own experience with using the same unbounded regular expressions on real-world licenses is that I have seen it take minutes just to process one regular expression on a single file, and this does not scale well when there are millions of files to process. Clearly, in terms of English language there is no maximum size on the length of a copyright statement. Using an unbounded regular expression is therefore correct in theory but difficult to use in practice. I have had to use size bounded regular expressions in order to have a scanning tool that will complete in a reasonable time. The problem in switching to bounded regular expressions is in deciding on what is an acceptable upper bound on the size, and this can really only be judged by experimentation against real-world licenses, and does then require on-going tweaking as new license variations are discovered.

Neither of these are problems with templatization per-se, and they are more to do with the extent and way in which they are currently applied.

Markup to add/consider

[JL] This is simply a list of various specific licenses that may need additional markup or things to consider related to the matching guidelines, to ensure we don't forget to add/edit later!

  • Apache-2.0 - instructions as to how to apply license, markup as optional? (from Kris)
  • MIT - "THE AUTHORS OR COPYRIGHT HOLDERS" - markup to be variable (from DMG's student paper)
  • add "noninfringment" and "non-infringement" and "non infringement" as equivalent words in Matching Guideline #8 list of words (from DMG's student paper)
  • add "contributors" and "co-contributors" and "co contributors" as equivalent words in Matching Guideline #8 list of words, needs some discussion (from DMG's student paper)
  • ISC license needs markup (and link fixed)