Defines the configuration elements for Spring OSGi support. Reference to a single OSGi service. Collection of OSGi services. The collection will automatically pick up the OSGi services that match the criteria. The dynamic nature is understood by the collection which will grow or shrink in size, as matching services come and go. The collection offers 'consistent' iterators so that clients can safely travers the services, at a certain point in time, without having to worry about the dynamics.