How to convert ISBN-13 without Dashes to ISBN-13 with dashes?

Our application makes extensive use of ISBN's. One of the process involves converting ISBN-13 without dashes to ISBN-13 with dashes and we had an application which does the job written in java. It's not working and we don't know the logic either now. After trying really hard searching on the net am still not able to figure out the logic behind the conversion.





To illustrate more clearly if we input the ISBN - 9780702039966 as input it should give 978-0-7020-3996-6.





Here are few more of the ISBN's-





9780080879116 - 978-0-08-087911-6


9780702039805 - 978-0-7020-3776-4


9780080958088 - 978-0-08-095808-8


9780323071079 - 978-0-323-07107-9


9780444529176 - 978-0-444-52917-6


9781437711493 - 978-1-4377-1149-3


9780323071147 - 978-0-323-07114-7





Could someone please explain me the logic behind this of how it is happening? With that I would try making an application of my own. Other sources of information for the same would also be highly welcome. Please let me know if you need any additional information.|||Have you considered asking Dewey Readmore Books?