We already confronted SEs with DLs to realize the differences between them.
We can compare the different categories of SEs with the different categories of
DLs. Basic-SE is similar to all DLs in the basic user interface, IR tools, and
network access. Furthermore, Basic-SE is similar to HDL since they both hold
metadata repositories rather than full items. A directory is even closer to a DL
than a Basic-SE, since it is humanly compiled and therefore has quality control.
But lets not forget it does not have domain focus and DL integrated services.
Meta-SE is somewhat similar to FDL in the sense that both generate on-the-fly
queries to other SEs/DLs to answer user queries. We elaborate more on the
differences between SEs and DLs in the next section.