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[protege-owl] Modeling change, source, uncertainty, contradiction?
johann.petrak at chello.at
Thu Aug 23 23:11:15 PDT 2007
Thank you, lots of interesting stuff and interesting pointers!
I will have to let this settle and also see where a practical
way to compromise is in my application.
Getting back to OWL I wonder if it would be possible to
have the cake and eat it: would it be possible to
introduce triples that give additional information
about properties (making a property the domain of another
property) which can also be searched,
but with the protege-owl framework ignoring
those triples for reasoning (e.g. when computing
a transitive closure)? I am aware that his would again
also provide limited functionality but in my case it
probably would be sufficient.
Thomas Russ wrote:
> On Aug 22, 2007, at 6:11 AM, Johann Petrak wrote:
>> Matt Williams wrote:
>>> As a very simple approach to modelling time, you could use
>>> time-interval-valid versions of the ontology. Not pretty, but
>>> might be
>> For my purpose, I would be more interested in searchability than
>> deductability. In other words, I do not want to make deductions based
>> on time -- it would be sufficient to find properties of instances
>> that are valid at a specific time. (So time would not be an issue
>> for classes, just for instances)
>> Naively I want an attribute "valid during" for each property/relation
>> between instances.
> This is generally tough to get without some sort of temporal
> reasoning system to keep the information separate. One approach that
> I worked on integrated such reasoning with a description logic system
> (LOOM, starting with version 2.1). The only reference to that is in
> the release notes, though:
> As Matt Williams indicated, sometimes a simple partitioning or
> context system will be sufficient, as long as the time granularity
> does not need to be too fine.
> Although you suggest that you don't care about deduction, in fact
> your desire to find items "valid at a specific time", which implies
> some form of reasoning that understands notions of temporal extent
> and persistence. Unless you are able to specify ALL of the specific
> times at which your fact is supposed to hold. But that quickly gets
> unwieldy. That generally means you want to have some type of (at
> least) interval reasoning capability so that you don't have to code
> the temporal constraints directly in any query that you write.
>> More generically I want several attributs: "valid during", "source"
>> The only thing I would need to do is to get the value of these
>> attributes out of the knowledge base and to search for triples
>> where these attributes match a specific pattern.
> This is where things start to get a bit trickier, since the searching
> interface will either need to understand the conventions for the
> temporal or attributive relationships or else you will need to do
> some reified version of the propositions. But if you reify them,
> then you will end up having to do any domain level reasoning on your
> It's a tricky problem.
>>> DL ontologies will not handle conflicting information. To do that,
>>> need to use a defeasible formalism. There is a little bit of work on
>>> ontologies & defeasibel reasoning.
>>> I have used argumentation & ontologies; there's a paper at
>>> http://acl.icnet.uk/~mw/WillliamsHunterICTAI07.pdf which also has
>>> references to the other approaches.
>> Thank you for the reference. I am not sure I need it at such a
>> complex level though, since I do not need a reasoner to
>> come up with sets of entailed or conflicting facts.
>> I think it would be sufficient for me to be able to model
>> something like
>> "source A indicates instanceX Rel1 instanceY"
>> "source B indicates instanceX notRel1 instanceY"
>> or put differently
>> instanceX Rel1-withattr: from source A instanceY
> This requires either some form of the frames-world facets, or more
> generally, a higher order logic, since you are making assertions
> about particular sentences rather than just making domain-level
> The straight-forward approach involves using higher-order logics.
> This allows attaching source and certainty values directly to
> sentences in the logic. But there are generally few such logics
> available, and they have somewhat limited reasoning. Some examples
> are CyC (<http://www.cycorp.com>) and PowerLoom (<http://www.isi.edu/
> isd/LOOM/PowerLoom/>). [Disclaimer: I work on the latter system]
> The alternative is to reify the relationships as instances in the
> logic. The reification will also work, but by doing so you give up
> any understanding by OWL of the fact that these reifications are
> properties of particular instances. It will also slightly complicate
> your querying, because instead of a query something like the
> following (using made-up pseudo-syntax):
> SELECT ?y WHERE (instanceX Rel1 ?y)
> you would need to query for something like
> SELECT ?y
> WHERE (?rel isa Relationship) and (subject ?rel instanceX) and
> (predicate ?rel Rel1) and (object ?rel ?y)
> With reification, you have a individual that represents the
> relationship, and that allows you to make arbitrary additional
> assertions about that relationship. This uses a technique similar to
> that used by OWL for representing N-ARY relationships. (Ref: <http://
>> So it comes down to attatching searchable arbitrary attributes
>> to properties/relations again.
> Well, they wouldn't be properties per se anymore if you used
> reification. Instead, the relationship would be an instance of
> something like Relationship with its own properties such as subject,
> predicate object. In other words, it would look like an RDF triple,
> about which you could express something else.
> In that sense, perhaps Matt is correct in that you might want to look
> at less constrained modeling systems such as RDF/RDFS instead of
> OWL. You can then make arbitrary assertions about any triple, as
> long as you were content to do any reasoning yourself.
>> Could it be that I am missing something totally elementary
>> here because it seems that should be something that is needed
>> all the time?
> Well, it's a hard problem, especially with regard to producing
> reasoners and query answering services over the more complicated
> logics. For one thing, having both the base relations and
> reifications of them introduce issues of keeping the two items
> synchronized. The usual solution to that is to use only the reified
> form, since that is the simplest. But then you don't get to treat
> those particular relationships as relationships that, say OWL, would
> understand. They would be instances that you would have to provide
> all the reasoning for.
>>> If you want to discuss this in more detail, email me off-list.
>>> Johann Petrak wrote:
>>>> I am pretty new to using Ontologies for knowledge represenation so
>>>> most of the tutorials and examples I have seen only are about
>>>> modeling some consistent set of unchanging facts.
>>>> However, in real word situations it is often necessary to deal
>>>> with knowledge or information that has one of the following
>>>> * a fact might change over time. More exactly, a property
>>>> might be valid during some period of time but not another.
>>>> Is it possible to model this in OWL ontologies and if yes,
>>>> what are common design patterns to do it?
>>>> * The fact that some instance has some property might be
>>>> known based on sources A and B but might not be confirmed
>>>> from source C. More problematic, it might contradict
>>>> information from source D. So instead of some fact just
>>>> "existing" we would like to model that it exists
>>>> "according to source A" but "not confirmed by source C"
>>>> and "not, according to source D"
>>>> Is it possible to model this?
>>>> * Sometimes it would be useful to attach a level of belief
>>>> to a fact. E.g. some instance having some property might
>>>> be likely but not certain.
>>>> These things are probably differently hard to model, if at
>>>> My biggest concern at the moment is change over time: for
>>>> most applications where I need some knowledge representation
>>>> it would be extremely important to be able to know that
>>>> e.g. some name was used during a certain time or that some
>>>> property existed during a certain period but not another.
>>>> I would be thankful for any hints you could give me or
>>>> any papers or sources you could point out where these
>>>> issues are discussed.
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