Open Source Licensing: Risk and Opportunity, Part One

“Let’s look in more detail at the obligations associated with
the copyleft licenses as exemplified by LGPL and GPL. There is a
significant amount of controversy surrounding the interpretation of
GPL and LGPL licenses. See, for example, the section “linking and
derived works” in the Wikipedia GPL article. The key concept that
determines obligations is the concept of “derivative work.” This
term has a legal definition that has a long history in copyright
law as it applies to various creative works. However, in the case
of software, there is legal ambiguity that has not been settled by
the courts. If we take a conservative view that any combination
through source code or linking constitutes a derivative work, the
GPL license clearly establishes that all derived works are to be
released under GPL. LGPL, on the other hand, makes a distinction
between different kinds of derived works. The LGPL license says
that “You may convey a Combined Work under terms of your
choice…” as longs as the user can “recombine or relink the
Application with a modified version of the Linked Version to
produce a modified Combined Work.” The implication is that if an
application uses a statically linked library, the application
distribution must deliver the source or object files to allow
re-assembling the application. In case of a dynamically linked
library, there is no such obligation because the application can be
re-assembled without the source or object files.”

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