Different licensing situations in software development - Part 7

As a part of this series, I am writing on software licensing models (software licensing and open source), particularly when you use software components inside your software product. For example, you could be using an open source software for parsing XML, instead of writing your own software for this purpose. The same thing could be repeated for any such open source software product that you may want to use.
Now, if you want to use a service (such as providing an email service, or having an online photo editor, or some other similar service), then it is easier to use open source software than if you are distributing your product as a shrink wrapped software. So, in the previous post, we talked about how using a CopyLeft license put terms on the final software that any derivative work based on the copyleft license would also need to be released on the same license as the copyleft software. Further, these rights cannot be subjected to revocation at a later point. So, if a free software does not ensure that derivative works be distributed under the same license, then it is not a copyleft license.
In addition, copyleft itself has weak and strong provisions. A weak copyleft provision allows that if a commercial software uses a copyleft software component, then only if the component is changed, then the changed section of code will need to be available for re-distribution. The concept of a weak copyleft provision is provided under the GNU Lesser General Public License and the Mozilla Public License (so you can find commercial software that actually incorporates component software that is licensed under the LGPL and MPL); while there are strong licenses such as the GNU General Public License that enjoins the entire incorporating software to be released under the same terms as the component.
What this also means is that if you are working with a commercial software company, then any use of licenses which have terms such as copyleft, GPL, LGPL, etc needs to be looked at very carefully before you go ahead with using such software. Using GPL would in almost all cases be totally ruled out.
More in the next post ...