Many journals allow to submit an extended version of a conference paper as, for example, Springer:
Expanded versions of papers which have previously appeared in conference proceedings will be considered and this request must be made at the time of submission; the authors must clearly state the conference publication and provide a statement of revisions/updates that have been made to the journal paper.
When writing such an extended version how do you reference the conference paper? I can imaging several possibilities:
- Treat it like every other paper in related work
- Ignore the conference paper completely and present all results as if for the first time.
- Clearly indicate that you wrote the conference paper as "... in  we showed that and shortly review the approach ..."
What is correct way to write an extended journal (in CS)?