In Semantic Web, are OWL EL, RL, QL all instances of DL? What is the difference? More inside.

Question

I'm using the pellet reasoner on a number of ontologies and have run the info method on a list of IRIs (in this case URLs). The two metrics that interest me are the DL Expressivity and OWL Profile.

The OWL Profiles I'm getting range from "OWL 2," "OWL 2 DL," "OWL 2 EL," "OWL 2 QL," "OWL 2 RL." When is says "OWL 2," does that mean the ontology is OWL 2 full? Are all the other variations DL? I have found a spec describing the different profiles (table 10 especially) [as a new user I can't post more than one hyperlink; thought the upcoming one was more important of two], but so far I haven't been able to answer this question for myself.

As for the "DL Expressivity," the very name implies that all the Expressivity codes (Such as ALCH, ALCH(D)) are DL. I have found this highly academic catalogue, so to speak, of the codes and their technical meaning in terms of complexity, but I need to know how to tell, at least generally, whether an ontology is DL or Full by looking at the Expressivities. Any help or links explaining these things would be most appreciated.

If it helps, I should also give some context for what I'm trying to do with this stuff. I'm just building a table from the "pellet info" data that has the ontology ID number (from the url list), the expressivity and OWL Profile for each, and also says whether that ontology is full, DL, or Lite. I look forward to your help, and thank you in advance!

Answer 1

If whatever is telling you (Pellet?) than an ontology is "OWL2" when it could otherwise state one of the profiles such as EL, QL or RL, then perhaps the ontology it is reporting about includes constructs that sit outside the expressivity of each of the profiles, but is otherwise included in the OWL2 specification.

As I understand it, each of the profiles are based on different description logics (DLs) that are geared towards different purposes:

• OWL2 (DL) is based on the description logic SROIQ, and is geared towards enabling ontologies with a high degree of expressivity in the language.
• OWL2-EL is based on EL++, which is geared towards scalable reasoning in the TBox (i.e., polymonial-time reasoning for most inference tasks such as classification).
• OWL2-QL is based on DL-Lite, which is geared towards scalable query answering in the ABox (when dealing with lots of instance data and a relatively simple TBox).
• OWL2-RL is based on Description Logic Programs (DLP), which has an expressivity that subsets that of OWL2 DL (the fragment that can be handled using a description logic).

As far as I can tell, the catalogue you've linked to is up-to-date, but is a bit hard to use if you aren't familiar with logics and can identify the constructs covered by each langauge. The W3C OWL2 profiles page summarizes the language expressivity of each of the profiles in OWL syntax. You could possibly refer to this to determine the intersecting expressivity of each of the OWL2 langauge profiles without having to interpret their semantics (in terms of DLs, which is hard to grasp unless you're comfortable with description logics, and in the case of OWL2-RL, description logic programs).

Lastly, note that the OWL1 'profiles' of Full, DL and Lite each correspond to yet other description logics:

• OWL1 DL corresponds to the description logic SHOIN.
• OWL1 Lite corresponds to the description logic SHIF.
• OWL1 Full corresponds to an undecidable logic that at least supersets SHOIN (though, I'm not quite sure what this is exactly! :-)