Classification framework in conceptual paper
Read more of the articles. Or at least read more of the article abstracts, before you begin classification. If a similar classification has already been used, just re-use that--it's already been demonstrated once. For a systematic review, the classification methods are analogous to the 'methods'--replication is a virtue. The papers you review are the data. If you bring new data, apply a good method, you will make a useful contribution.