Tag Archives: OWL

Carl Hewitt – Actor model, OWL, knowledge inconsistency and paraconsistent logic

ITConversations published recently Jon Udell’s interview with Carl Hewitt. In this interview – “Interdependent Message-Passing ORGs”, Carl Hewitt shares his ideas about distributed computations, Actor model, inconsistent knowledge, paraconsistent logic and semantic web.

Carl Hewitt’s work has been an inspiration to me for more than 20 years. Knowledge inconsistency is a fundamental reality of our life. When we build computer systems, we can ignore it, we can try to create artificial boundaries, artificial worlds with “guaranteed” knowledge consistency. Alternative approach is to accept from the beginning that we have to deal with inconsistency and create systems that can represent inconsistent knowledge, reason within inconsistent knowledge bases and utilize mechanisms which help to keep inconsistency “under control”.

I made the choice many years ago in favor of this alternative approach and used it in building many computer systems over the years. Our recent project – Ontopedia PSI server is not an exception. Ontopedia PSI server allows to represent opinions from various sources, including contradictory opinions. Ontopedia’s reasoning engine is justification based (as everything in Ontopedia – work in progress :) which means that decision about each assertion is based on comparison between various opinions and their justifications. Reasoning inside of Ontopedia PSI server is paraconsistent. Inference engine can find contradictory assertions in some areas of Ontopedia’s knowledge base. Local contradictions do not prevent reasoning engine from inferring reasonable assertions in other areas of knowledge base and there is no ‘explosion of assertions’.

Reasoning in Ontopedia PSI server is also ‘adaptive’. We anticipate that when various sources ‘see’ results of comparison between various opinions and ‘see’ consequences of their statements in several ‘steps ahead’, then sources can change their original opinions.

Ontopedia PSI server actually ‘likes’ contradictions. Contradictions are starting points of identifying errors, negotiations, improving knowledge models and as a result – knowledge evolution.


Interdependent Message-Passing ORGs, interview on ITConversations

2008 Semantic Technology Conference: random observations

I am back from Semantic Technology Conference. It is becoming bigger and bigger each year. This year there were more than hundred sessions, full day of tutorials, product exhibition. It was quite crowded and energizing.

Just some random observations:

Oracle improves RDF / OWL support in 11g database, considers RDF/OWL as strategic/enabling technologies which will be leveraged in future versions of Oracle products.

Yahoo uses RDF to organize content on various web sites. It also introduced SearchMonkey – extension to Yahoo search platform which allows to provide more detailed information about information resources.

– Consumer oriented web sites powered by semantic technologies are here. Twine, Freebase, Powerset are good examples, more to come.

Resource Oriented Architecture and RDF could be a very powerful combination. More and more people understand the value of exposing data through URIs in the form of information resources.
Linked Data initiative looks quite interesting.

– Some advanced semantic applications use knowledge representation formalisms that go beyond basic RDF/OWL model.
But RDF/OWL can be used to surface/exchange information based on W3C standards. Lots of discussions about
information provenance, trust, “semantic spam”.

– It looks like there is a workable solution (compromise) for ’Web’s Identity Crisis’. The idea is to reserve HTTP 303 (“See Other”) code for indication of “Concept URIs”. 303 response should include an additional URI for “See Other” information resource. This approach combined
with new PURL -like servers allows to keep RDF “as is” and to implement something close to the idea of Published Subject Identifiers

Franz demonstrated a new version of AllegroGraph 64-bit RDFStore. Franz implemented support for Named Graphs (can be used for representing weights, trust factors, provenance)
and incorporated geospatial and temporal libraries. Named Graphs allow to deal with contexts using RDF.

– Text analysis tools become better and better. Interesting example is AllegroGraph.
Incorporating natural language processors allows to extract entities and relationships with reasonable level of precision (News Portal sample).

Doug Lenat did a great presentation on the conference about the history of Cyc project. It looks like in 5-10 years we can expect “artificial intelligent assistants” with quite sophisticated abilities to reason.