Is each version of a software considered a &quot;derivative work&quot;?
<blockquote>
<p>Originally asked in <a href="https://softwareengineering.stackexchange.com/posts/438503/edit">Software Engineering</a> but a user raised it is more a legal question than an engineering one.</p>
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<p>Let's suppose there is a software at version <code>a1</code> in code repository <code>A</code> on an online code hosting website. Let's suppose</p>
<ul>
<li>the original author updated it and made a version <code>a2</code>, then <code>a3</code>.</li>
<li>Another person comes along, forked <code>a1</code> to another code repository <code>B</code>, then modified it resulting their own <code>b2</code>, then modified <code>b2</code> again and resulted in <code>b3</code>.</li>
<li>All versions are available online - <code>a1</code>, <code>a2</code>, <code>b2</code> are available in the code commit history, and <code>a3</code>, <code>b3</code> are available on the home page.</li>
</ul>
<pre><code>a1 -- a2 -- a3
  `-- b2 -- b3
</code></pre>
<p><strong>Question: how many derivative works of the software exist in this scenario?</strong></p>
<p>My initial instinct is <strong>one</strong>, because there is the original code repository <code>A</code>, and a forked-and-modified repository <code>B</code> which is the derivative work. But I realized the answer <em>might</em> be <strong>four</strong> (that is, <code>a2</code>, <code>a3</code>, <code>b2</code>, <code>b3</code> all count as derivative works of the original code -- but <strong>not sure</strong>), given that in the copyright law (using <a href="https://www.law.cornell.edu/uscode/text/17/101" rel="nofollow noreferrer">US copyright law</a> as an example):</p>
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<p>A “derivative work” is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications which, as a whole, represent an original work of authorship, is a “derivative work”.</p>
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<p>The definition given in the <a href="https://www.apache.org/licenses/LICENSE-2.0" rel="nofollow noreferrer">Apache 2.0 license</a> is more direct:</p>
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<p>&quot;Derivative Works&quot; shall mean any work, whether in Source or Object form, that is based on (or derived from) the Work and for which the editorial revisions, annotations, elaborations, or other modifications represent, as a whole, an original work of authorship.</p>
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<p>I think a key point a software is different from a book/painting/movie is that software is very much a &quot;live&quot; thing - that is, software is constantly being updated after being &quot;published&quot;. Especially, each small iteration (commit) of an open source project is accessible publicly, instead of periodically being made public after accumulating a few months' works behind the scene.</p>

<h2>Four</h2>
<p>Yes, each version is a derivative work, as mentioned in <a href="https://www.copyright.gov/circs/circ14.pdf" rel="nofollow noreferrer">https://www.copyright.gov/circs/circ14.pdf</a></p>
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<p>The following are examples of the many different types of derivative works:<br>
...<br>
A new version of an existing computer program</p>
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copyright software open-source-software derivative-work