publishing a conference paper in a journal some years ago (2007) I have published a  paper in a conference as a poster paper. Now I want to send it to a journal and change the affiliation, or maybe some minor changes. I didn't see any policy about a previous published paper in a conference, however there is a policy as the following:


  The submission has not been previously published, nor is it before
  another journal for consideration (or an explanation has been provided
  in Comments to the Editor).


Could I send my paper to this journal? 

Is it a normal thing to first publish a paper in  a conference and then trying to send it to a journal?
In my field this would be not only acceptable, but expected, as the review process for conferences is less stringent and the submitted abstracts are substantially less detailed than a full manuscript. A conference presentation is viewed almost as a necessary step to publication: present the first interpretation of the results, get feedback from colleagues, and incorporate changes into the full-length manuscript. 

My only concern would be if the conference paper was closer to a full manuscript, both in length and in the rigorousness of the review process.