Hadronic observables at relativistic energies: Anything strange with strangeness?

We calculate p, π^±, K^±, and Λ(+Σ⁰) rapidity distributions and compare to experimental data from SIS to SPS energies within the Ultrarelativistic-Quantum-Molecular Dynamics and Hadron-String Dynamics transport approaches that are both based on string, quark, diquark $(q,$ q̄, $qq,$ q̄q̄), and hadronic degrees of freedom. The two transport models do not include any explicit phase transition to a quark-gluon plasma. It is found that both approaches agree rather well with each other and with the experimental rapidity distributions for protons, {Λ}'s, π^±, and K^±. In spite of this apparent agreement both transport models fail to reproduce the maximum in the excitation function for the ratio K⁺/π⁺ found experimentally between 11 and 40 A GeV. A comparison to the various experimental data shows that this ``failure'' is dominantly due to an insufficient description of pion rapidity distributions rather than missing ``strangeness.'' The modest differences in the transport model results---on the other hand---can be attributed to different implementations of string formation and fragmentation that are not sufficiently controlled by experimental data for the ``elementary'' reactions in vacuum.