Realization of a Context-Dependent Access Control Mechanism on a Commercial Platform

Recently, context-dependent access control mechanisms were established: Information about the state of a business process is combined with general knowledge about a person to grant or revoke access to sensitive data. Though being understood very well in principle, many different problems arise when context-dependent access control is realized for an application of practical relevance on a concrete platform. We present in this paper the implementation of context-dependent access control for a client-/server-based hospital information system. The system is WindowsNT-based and is implemented with MS Visual Basic on an MS SQL Server database. Additionally there is an Action Technology workflow system that provides the required context information. We will demonstrate how the context-dependent access control can be implemented taking into account the constraints of the given platform. Keywords Context-dependency, access control, business processes, implementation 1 INTRODUCTION In (Hol..

Strong magnetoelastic coupling at the transition from harmonic to anharmonic order in NaFe(WO4)(2) with 3d(5) configuration

The crystal structure of the double tungstate NaFe(WO4)(2) arises from that of the spin-driven multiferroic MnWO4 by inserting nonmagnetic Na layers. NaFe(WO4)(2) exhibits a three-dimensional incommensurate spin-spiral structure at low temperature and zero magnetic field, which, however, competes with commensurate order induced by magnetic field. The incommensurate zero-field phase corresponds to the condensation of a single irreducible representation but it does not imply ferroelectric polarization because spirals with opposite chirality coexist. Sizable anharmonic modulations emerge in this incommensurate structure, which are accompanied by large magnetoelastic anomalies, while the onset of the harmonic order is invisible in the thermal-expansion coefficient. In magnetic fields applied along the monoclinic axis, we observe a first-order transition to a commensurate structure that again is accompanied by large magnetoelastic effects. The large magnetoelastic coupling, a reduction of the b lattice parameter, is thus associated only with the commensurate order. Upon releasing the field at low temperature, the magnetic order transforms to another commensurate structure that considerably differs from the incommensurate low-temperature phase emerging upon zero-field cooling. The latter phase, which exhibits a reduced ordered moment, seems to be metastable