ActsTrk::JSONDeviceMagFieldProviderSvc Node1 ActsTrk::JSONDeviceMagField ProviderSvc - m_detStore - m_deviceFieldProviderTool - m_magFieldFile - m_hostMagFieldObjectName - m_deviceMagFieldObjectName + initialize() * m_magFieldFile * m_hostMagFieldObjectName * m_deviceMagFieldObjectName Node2 AthService   - AthService() - AthService() - operator=() Node2->Node1 Node3 AthCommonMsg< Service >   + msg() + msgLvl() Node3->Node2 Node4 Service     Node4->Node3