java.lang.NoClassDefFoundError: org/eclipse/ui/views/properties/IPropertySource

Question

I have a GEF plugin that needs to show the Properties tab. I have added the IPropertySource interface and implemented its methods.In the model class,which is implementing IAdaptable, the following has been included:

@Override
    public Object getAdapter(Class adapter) {
        if (adapter == IPropertySource.class) {
            propertySource = new ParentPropertySource(parent);
            return propertySource;
        }
        return null;

    }

I have also added the "org.eclipse.ui.views" in Dependencies in plugin.xml But unable to debug as to why this runtime exception is occuring.

Kindly guide.