license because we specifically seek to liberalize the rights afforded to

those who make derivative works. In GPL, we reach as far as copyright law

allows. In LGPL, we want to draw a line that allows some derivative works

copyright law would otherwise prohibit if the copyright holder exercised

his full permitted controls over the work.

In the effort to allow certain proprietary derivative works and prohibit

others, LGPL distinguishes between two classes of derivative works:

``works based on the library,'' and ``works that use the library.''  The

distinction is drawn on the bright line of binary (or runtime) derivative

works and source code derivatives. We will first consider the definition

\worki{} is neither a ``work that uses the library'' nor a ``work based on

the library.''  If the answer to the first question is ``no,'' but the

answer to the second question is ``yes,'' then an investigation into

whether or not \worki{} is in fact a ``work based on the library'' is

warranted.

In short, a ``work based on the library'' could be defined as any

derivative work of LGPL'd software that cannot otherwise fit the

definition of a ``work that uses the library.''  A ``work based on the

library'' extends the full width and depth of copyright derivative works,

in the same sense that GPL does.

specific set of works that were based on the library. Once such

distinctions are established, the licensing for each component can be

considered independently and the LGPL applied to each work as

prescribed.

In our discussion of the definition of ``works that use the library,'' we

left out a few more complex details that relate to lower-level programming

details. The fourth paragraph of LGPL's \S 5 covers these complexities,

and it has been a source of great confusion. Part of the confusion comes

because a deep understanding of how compiler programs work is nearly

this edge condition. The intent of clarifying this edge condition is

primarily to quell the worries of software engineers who understand the

level of verbatim code copying that a compiler often does, and to help

them understand that the full implications of LGPL are the same regardless

of the details of the compilation progress.

\label{lgpl-section-6}

Now that we have established a good working definition of works that

``use'' and works that ``are based on'' the library, we will consider the

rules for distributing these two different works.

The rules for distributing ``works that use the library'' are covered in

The remaining options in \S 6 are very similar to the other choices

provided by GPL \S 3. There are some additional options, but time does

not permit us in this course to go into those additional options. In

almost all cases of distribution under LGPL, either \S 6(a) or \S 6(b) are

exercised.

Essentially, ``works based on the library'' must be distributed under the

same conditions as works under full GPL\@. In fact, we note that LGPL's

\S 2 is nearly identical in its terms and requirements to GPL's \S 2.

There are again subtle differences and additions, which time does not

permit us to cover in this course.