1. Bittner, K.: Use Case Modeling. Addison-Wesley Longman Publishing Co., Inc, Boston, MA, USA (2002)
2. Hirschfeld, R., Costanza, P., Nierstrasz, O.: Context-oriented Programming. Journal of Object Technology (submitted, 2007)
3. Dardenne, A., van Lamsweerde, A., Fickas, S.: Goal-directed requirements acquisition. In: 6IWSSD: Selected Papers of the Sixth International Workshop on Software Specification and Design, pp. 3–50. Elsevier Science Publishers B. V, Amsterdam (1993)
4. Jackson, M.: Problem frames: analyzing and structuring software development problems. Addison-Wesley Longman Publishing Co. Inc, Boston, MA, USA (2001)
5. Steels, L.: Kennissystemen. Addison-Wesley, Reading, MA, USA (1992)