In the filter area, you can create filters for attribute values. If you pick an attribute with of string type, e.g. the attribute "Class", you can still select e.g. <= in the comparator in the filter. They should be reserved for numerical values.

This is the exception you get if you try to compare with <= on strings:

!ENTRY org.eclipse.ui 4 0 2016-03-02 13:16:17.605
!MESSAGE Error occurred during status handling
!STACK 0
java.lang.RuntimeException: Unknown comparison kind
at com.oracle.jmc.common.item.ItemFilters.buildEqualityFilter(ItemFilters.java:544)
at com.oracle.jmc.ui.misc.FilterEditor.buildFilter(FilterEditor.java:922)
at com.oracle.jmc.ui.misc.FilterEditor.access$10(FilterEditor.java:910)
at com.oracle.jmc.ui.misc.FilterEditor$OperationEditingSupport.doSetValue(FilterEditor.java:801)
at com.oracle.jmc.ui.misc.FilterEditor$OperationEditingSupport.setValue(FilterEditor.java:787)
at org.eclipse.jface.viewers.EditingSupport.saveCellEditorValue(EditingSupport.java:113)
at org.eclipse.jface.viewers.ColumnViewerEditor.saveEditorValue(ColumnViewerEditor.java:463)
at org.eclipse.jface.viewers.ColumnViewerEditor.applyEditorValue(ColumnViewerEditor.java:319)
at org.eclipse.jface.viewers.ColumnViewerEditor.handleEditorActivationEvent(ColumnViewerEditor.java:446)
at org.eclipse.jface.viewers.ColumnViewer.triggerEditorActivationEvent(ColumnViewer.java:676)
at org.eclipse.jface.viewers.ColumnViewer.handleMouseDown(ColumnViewer.java:651)
at org.eclipse.jface.viewers.ColumnViewer.access$0(ColumnViewer.java:647)
at org.eclipse.jface.viewers.ColumnViewer$1.mouseDown(ColumnViewer.java:96)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:192)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4362)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1113)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4180)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3769)
at org.eclipse.ui.statushandlers.WorkbenchErrorHandler.showStatusAdapter(WorkbenchErrorHandler.java:102)
at org.eclipse.ui.statushandlers.WorkbenchErrorHandler.handle(WorkbenchErrorHandler.java:50)
at com.oracle.jmc.rcp.application.BlockingWorkbenchErrorHandler.handle(BlockingWorkbenchErrorHandler.java:23)
at org.eclipse.ui.internal.WorkbenchErrorHandlerProxy.handle(WorkbenchErrorHandlerProxy.java:31)
at org.eclipse.ui.statushandlers.StatusManager.handle(StatusManager.java:189)
at org.eclipse.ui.internal.JFaceUtil$3.show(JFaceUtil.java:73)
at org.eclipse.jface.util.SafeRunnable.handleException(SafeRunnable.java:63)
at org.eclipse.core.runtime.SafeRunner.handleException(SafeRunner.java:75)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:44)
at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:50)
at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:173)
at org.eclipse.jface.viewers.CellEditor.fireApplyEditorValue(CellEditor.java:333)
at org.eclipse.jface.viewers.ComboBoxViewerCellEditor.applyEditorValueAndDeactivate(ComboBoxViewerCellEditor.java:257)
at org.eclipse.jface.viewers.ComboBoxViewerCellEditor.focusLost(ComboBoxViewerCellEditor.java:264)
at org.eclipse.jface.viewers.ComboBoxViewerCellEditor$4.focusLost(ComboBoxViewerCellEditor.java:123)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:143)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4362)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1113)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1137)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1122)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:788)
at org.eclipse.swt.custom.CCombo.handleFocus(CCombo.java:919)
at org.eclipse.swt.custom.CCombo$2.handleEvent(CCombo.java:147)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.filterEvent(Display.java:1266)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1112)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1137)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1118)
at org.eclipse.swt.widgets.Control.sendFocusEvent(Control.java:2855)
at org.eclipse.swt.widgets.Widget.wmSetFocus(Widget.java:2477)
at org.eclipse.swt.widgets.Control.WM_SETFOCUS(Control.java:5309)
at org.eclipse.swt.widgets.Tree.WM_SETFOCUS(Tree.java:7132)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4732)
at org.eclipse.swt.widgets.Tree.windowProc(Tree.java:6024)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5050)
at org.eclipse.swt.internal.win32.OS.SetFocus(Native Method)
at org.eclipse.swt.widgets.Tree.WM_LBUTTONDOWN(Tree.java:6703)
at org.eclipse.swt.widgets.Control.windowProc(Control.java:4698)
at org.eclipse.swt.widgets.Tree.windowProc(Tree.java:6024)
at org.eclipse.swt.widgets.Display.windowProc(Display.java:5050)
at org.eclipse.swt.internal.win32.OS.DispatchMessageW(Native Method)
at org.eclipse.swt.internal.win32.OS.DispatchMessage(OS.java:2549)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3767)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1127)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1018)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:156)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:654)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:337)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:598)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
at com.oracle.jmc.rcp.application.Application.start(Application.java:36)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:380)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:235)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:520)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:669)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:608)
at org.eclipse.equinox.launcher.Main.run(Main.java:1515)
at org.eclipse.equinox.launcher.Main.main(Main.java:1488)