The authors present the result of a comparative analysis of different programming languages and systems that claim the label object-oriented. The concepts of persistence, concurrency, composition, perspective, distribution, location and mobility, communication, encapsulation, autonomy, and mutation are presented as characteristics of physical objects. Classifications are used by people to organize their knowledge of physical objects. The authors discuss the appearance of the concepts in programming languages and illustrate them through the different investigated languages. They survey a conceptual framework that gives the physical-world metaphor its due and that will be supported in the TIE-system.< >