  Context: We present the soft X-ray properties obtained in the ROSAT All-Sky
survey and from pointed PSPC observations for the AGN in the complete
flux-density limited Caltech-Jodrell Bank flat spectrum sample (hereafter CJF).
CJF is a VLBI survey (VLBA observations at 5 GHz) of 293 AGN with detailed
information on jet component motion. Aims: We investigate and discuss the soft
X-ray properties of this AGN sample and examine the correlations between X-ray
and VLBI properties, test beaming scenarios, and search for the discriminating
properties between the sub-samples detected and not detected by ROSAT. Methods:
Comparing the observed and the predicted X-ray fluxes by assuming an Inverse
Compton (IC) origin for the observed X-rays, we compute the beaming or Doppler
factor and contrast the Doppler factors with other beaming indicators derived
from the VLBI observations, such as the value of the expansion velocity, and
the observed and intrinsic brightness temperature. In addition, we investigate
the large-scale radio structure of the AGN and the difference between the pc-
and kpc-scale structure (misalignment) with regard to the X-ray
observations.Results: We find a nearly linear relation between X-ray and radio
luminosities, and a similar but less stringent behaviour for the relation
between optical and X-ray luminosities. The quasars detected by ROSAT have a
different $\beta_{\rm app}$-redshift relationship compared to the non-detected
ones. ROSAT-detected sources tend to reveal extended large-scale radio
structures more often. Conclusions: We conclude that beaming alone cannot
explain the observed dichotomy of ROSAT detection or non-detection and assume
that the large-scale jet structure plays a decisive role.
