Editing Semantic Web (section)

== Challenges ==
Some of the challenges for the Semantic Web include vastness, vagueness, uncertainty, inconsistency, and deceit. [[Automated reasoning system]]s will have to deal with all of these issues in order to deliver on the promise of the Semantic Web.
* Vastness: The World Wide Web contains many billions of pages. The [[SNOMED CT]] [[medical terminology]] [[ontology (information science)|ontology]] alone contains 370,000 [[Class (computer programming)|class]] names, and existing technology has not yet been able to eliminate all semantically duplicated terms. Any automated reasoning system will have to deal with truly huge inputs.
* Vagueness: These are imprecise concepts like "young" or "tall". This arises from the vagueness of user queries, of concepts represented by content providers, of matching query terms to provider terms and of trying to combine different [[knowledge base]]s with overlapping but subtly different concepts. [[Fuzzy logic]] is the most common technique for dealing with vagueness.
* Uncertainty: These are precise concepts with uncertain values. For example, a patient might present a set of symptoms that correspond to a number of different distinct diagnoses each with a different probability. [[Probabilistic logic|Probabilistic]] reasoning techniques are generally employed to address uncertainty.
* Inconsistency: These are logical contradictions that will inevitably arise during the development of large ontologies, and when ontologies from separate sources are combined. Deductive reasoning fails catastrophically when faced with inconsistency, because [[Principle of explosion|"anything follows from a contradiction"]]. [[Defeasible reasoning]] and [[Paraconsistent logic|paraconsistent reasoning]] are two techniques that can be employed to deal with inconsistency.
* Deceit: This is when the producer of the information is intentionally misleading the consumer of the information. [[Cryptography]] techniques are currently utilized to alleviate this threat. By providing a means to determine the information's integrity, including that which relates to the identity of the entity that produced or published the information, however [[credibility]] issues still have to be addressed in cases of potential deceit.

This list of challenges is illustrative rather than exhaustive, and it focuses on the challenges to the "unifying logic" and "proof" layers of the Semantic Web. The World Wide Web Consortium (W3C) Incubator Group for Uncertainty Reasoning for the World Wide Web<ref>{{Cite web|title=W3C Uncertainty Reasoning for the World Wide Web|url=https://www.w3.org/2005/Incubator/urw3/Overview.html|access-date=2021-05-14|website=www.w3.org}}</ref> (URW3-XG) final report lumps these problems together under the single heading of "uncertainty".<ref>{{cite web|url=http://www.w3.org/2005/Incubator/urw3/XGR-urw3-20080331/Overview.html|title=Uncertainty Reasoning for the World Wide Web|website=W3.org|access-date=20 December 2018}}</ref> Many of the techniques mentioned here will require extensions to the Web Ontology Language (OWL) for example to annotate conditional probabilities. This is an area of active research.<ref>{{cite journal |last=Lukasiewicz |first=Thomas |author2=Umberto Straccia |title=Managing uncertainty and vagueness in description logics for the Semantic Web |doi=10.1016/j.websem.2008.04.001 |volume=6 |issue=4 |journal=Web Semantics: Science, Services and Agents on the World Wide Web |pages=291–308|year=2008 |url=http://faure.isti.cnr.it/~straccia/download/papers/JWS08/JWS08.pdf }}</ref>