A method comprising: determining, by a controller device for a virtual network, a set of two or more related processes executed by respective devices (12, 16, 18) in the virtual network, the related processes including a first process executed by a first device of a plurality of devices that form a physical network and a second, related process executed by a second, different device of the plurality of devices, wherein the virtual network is executed as an overlay network formed over the physical network and between virtual switches executed by the plurality of devices including a first virtual switch executed by the first device and a second virtual switch executed by the second device, and wherein determining the set of two or more related processes comprises forming the set to include processes that perform similar operations on different instances of respective data; receiving, by the controller device, data for the set of two or more related processes from the respective devices; aggregating, by the controller device, the data for the set of two or more related processes to form aggregated data for the set of two or more related processes, wherein the aggregated data comprises data for a User-Visible Entity, UVE wherein the UVE defines one or more attributes for which values are to be extracted from the received data for the set of two or more related processes, wherein the UVE defines the one or more attributes for a tier in which the set of two or more related processes are executed, and wherein aggregating comprises: extracting values for the one or more attributes defined by the UVE, and aggregating the values for the one or more attributes; and generating, by the controller device, a report from the aggregated data, the report including data indicative of a fault in the virtual network. determining, by a controller device for a virtual network, a set of two or more related processes executed by respective devices (12, 16, 18) in the virtual network, the related processes including a first process executed by a first device of a plurality of devices that form a physical network and a second, related process executed by a second, different device of the plurality of devices, wherein the virtual network is executed as an overlay network formed over the physical network and between virtual switches executed by the plurality of devices including a first virtual switch executed by the first device and a second virtual switch executed by the second device, and wherein determining the set of two or more related processes comprises forming the set to include processes that perform similar operations on different instances of respective data; receiving, by the controller device, data for the set of two or more related processes from the respective devices; aggregating, by the controller device, the data for the set of two or more related processes to form aggregated data for the set of two or more related processes, wherein the aggregated data comprises data for a User-Visible Entity, UVE wherein the UVE defines one or more attributes for which values are to be extracted from the received data for the set of two or more related processes, wherein the UVE defines the one or more attributes for a tier in which the set of two or more related processes are executed, and wherein aggregating comprises: extracting values for the one or more attributes defined by the UVE, and aggregating the values for the one or more attributes; and extracting values for the one or more attributes defined by the UVE, and aggregating the values for the one or more attributes; and generating, by the controller device, a report from the aggregated data, the report including data indicative of a fault in the virtual network.