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Put your recommendations in the appropriate subsection.

The following was cut from section 6.3 because it is implementation specific and was not appropriate for there. It may work better as part of the Recommendations

Any standardization effort must start from the existing standards for knowledge representation on the semantic web. Predominantly this means consistency with OWL and related standards such as ruleML but it also implies that the core underlying representation must be expressible in a description logic format. This means (at minimum) that the forms of uncertainty described in 3.1 must be expressible.

7.1. Overall Conclusions of XG Work

The aforementioned use cases demonstrate that there are two very different kinds of uncertainty that we need to consider in standardization.

a) uncertainty inherent in the data.

b) uncertainty reasoning for the processing and presentation of information

Each of (a) and (b) represent different standardization motivations and requirements.

In the first case, the standardization should be done at the representation level. When sharing information that has an inherent level of uncertainty or vagueness it's useful to have a single syntactical system so that people can identify and process this information quickly. These kinds of use case require something like a probabilistic extension to OWL. We want to be able to pass on information that Study X shows that people with property Y have an X% increased likelihood of this disease, or that the probability of a four of a kind given pocket Aces and an Ace in the flop is .043. This simply requires a standard syntax.

But many of the use cases we've considered involved uncertainty reasoning on the part of the tools used to access and share web information, not the information itself. For example, if a web service uses uncertainty reasoning to find and rank hotel rooms for me, the probabilistic information won't reside on the web. In such situations the role of standardization is different and the motivation may be less clear. After all, if the hotel room information is useful and rankings are roughly accurate, many users will be unconcerned with the reasoning process or the uncertainties attached to the rankings. So, here, we'd want to use standardization for a different purpose. It would be used to represent metainformation about the reasoning models and assumptions. And it would also play a different role, e.g., developing trust models, finding compatible web services. However, it could also require a very extensive representation task. Standardization questions here include determining how to represent this information, how detailed it would be, where it would reside.


I don't quite agree with the above distinction. Actually in my view b) cannot come unless you already have a). But anyway, let me put my view. From my experience W3C has never standardized any reasoning algorithm or procedure. Actually the most important thing, which W3C is focusing on, is to standardize a representation format with which one would be able to communicate knowledge or information. Then, what one would do with that knowledge (reason, not reason or whatever) is a different story.

So for example OWL (roughly) is a spec for interchanging ontologies written in Description Logics. On the other the OWL spec nowhere does it say that one should do sound and complete reasoning with OWL using reasoning algorithm X. As a matter of fact there are many different ways to do reasoning in DLs. A source Y could also choose to do incomplete reasoning with the OWL file that Z transmitted to him, in order to gain in efficiency. But, the point is that Y and Z have an agreed format upon which they could communicate over the Web (to some extend).

So the biggest goal is a format to represent uncertainty in order to have an agreed way to communicate. Since W3C has already specified formats for representing knowledge, like RDF, OWL, and in the future RIF, we could use these formats and build on them. So we could investigate a Pr-OWL format, a Fuzzy-OWL format or make profiles on them according to the type of uncertainty that we will identify as important to be represented (remember that we cannot represent everything but a tradeoff is usually made).


[KenLaskey] I agree with the comments from Giorgos but I do not see these as being inconsistent with the previous text on which he is commenting. Our eventual goal is to have a standard syntax and related semantics for conveying uncertainty information, and that information must cover both inherent uncertainty in the data and uncertainty connected to results of processing that data. The two are certainly related and it may take further work to say whether we need separate portions of the syntax for each or whether a single syntax covers the entire range. [/KenLaskey]

7.3. Specific Recommendations for Standardization

It is acknowledged that while uncertainty is pervasive in both normal life and its reflections on the Web, it is not always necessary to characterize this uncertainty. However, there are significant instances where knowledge of uncertainties could be used to positively support decision making, and it is with such instances in mind that the URW3-XG makes the following recommendations:

  1. Whereas we have demonstrated use cases for which uncertainty can have a significant effect on the conclusions that can be drawn from viewing and processing information available on the World Wide Web, we believe a principled means for expressing uncertainty will increase the usefulness of Web-based information and believe a standard way of representing that information should be developed.
  2. Whereas the different use cases appear to lend themselves to different uncertainty formalisms, the standard representation should provide a means to unambiguously identify the formalism providing the context for assigning other uncertainty characteristics and values.
  3. Whereas different uncertainty formalisms assign values to properties specifically related to the underlying meaning and processing of these values, the representation should support defining different standard properties for each formalism without requiring changes to the representation itself.
  4. Whereas consistent understanding and processing must be enabled both within and across uncertainty formalisms, adjunct specification should be developed for the most commonly used uncertainty formalisms, as discussed in section 4. Such adjunct specifications would not be intended to prescribe an exclusive set of relevant formalisms but merely those found most useful at that time, with the ability to expand the set as circumstances might indicate to be prudent.
  5. Whereas uncertainty can be present anywhere, the representation should support associating uncertainty with any property or value expressible across the Web.

The recommendations point to the desirability of having a means to annotate information with relevant uncertainty information. The mechanism could be similar to that specified under Semantic Annotations for WSDL and XML Schema(SAWSDL) (, where the annotation approach is described as follows:

The specification defines how semantic annotation is accomplished using references to semantic models, e.g. ontologies. Semantic Annotations for WSDL and XML Schema (SAWSDL) does not specify a language for representing the semantic models. Instead it provides mechanisms by which concepts from the semantic models, typically defined outside the WSDL document, can be referenced from within WSDL and XML Schema components using annotations.

In the realm of uncertainty representation, we would specify uncertainty models and uncertainty annotations rather than SAWSDL's semantic counterparts. For such uncertainty annotations, a possible standard would need to support both inherent uncertainty in the data and uncertainty connected to results of processing that data, but at this point it is unclear whether there is a need for separate portions of the syntax for each data and processing uncertainty or whether a single syntax would be able to cover the entire range.

In addition, a question that remains with this approach but one which is outside the scope of the URW3-XG is whether existing languages (e.g. OWL, RDFS, RIF) are sufficiently expressive to support the necessary annotations. If so, the development of such annotations might merely require work on a more complete uncertainty ontology and possibly rules; otherwise, the expressiveness of existing languages might need to be extended. As an example of the latter, it might be advisable to develop a probabilistic extension to OWL (e.g. PR-OWL) or a Fuzzy-OWL format or profiles associated with the type of uncertainty to be represented. Further work is required to investigate the adequacy of the existing languages against the compiled use cases.

An eventual goal in continuing the current work would be to define a format to represent uncertainty in an agreed upon way to enable reliable communications for situations such as the compiled use cases. The work of the URW3-XG has made a significant contribution in defining the problem space and identifying continuing work. These questions will likely be the subject of discussion at a proposed 4th Uncertainty Reasoning for the Semantic Web (URSW) workshop at ISWWC 2008, and just as the 2nd URSW workshop decided to pursue the question of uncertainty representation through what became the URW3-XG, a proposal for continued work may be an output of the 2008 URSW workshop.