Loki Presentation of Logic-based Semantic Wiki

Abstract

TOOL PRESENTATION: The paper presents a semantic wiki, called Loki, with strong logical knowledge representation using rules. The system uses a coherent logic-based representation for semantic annotations of the content and implementing reasoning procedures. The representation uses the logic programming paradigm and the Prolog programming language. The proposed architecture allows for rule-based reasoning in the wiki. It also provides a compatibility layer with the popular Semantic MediaWiki platform, directly parsing its annotations.

Motivation

Architecture

A prototype implementation of Loki, called PlWiki (Prolog Wiki), has been de

veloped [ 2,4 ]. The main goal of the system design is to deliver a generic and exible solution. Thus, instead of modifying an existing wiki engine or implementing a new one, an extension of the DokuWiki 8 system has been developed.

The architecture can be observed in Fig. 1. The stack is based on a simple runtime including the Unix environment with the Unix lesystem, Apache web server and PHP stack. Using this runtime, a standard DokuWiki installation is run. The Loki functionality is implemented with the use of Dokuwiki plugins allowing to enrich the wikitext with semantic annotations and Prolog clauses, as well as run the SWI-Prolog interpreter. It is also possible to extend the wikitext with explicit semantic information encoded using RDF and OWL representation. This layer uses the Semantic Web library provided by SWI-Prolog. t x e t lain wiki p xte ogl t o iik Pr w +

F D R

L W O

XTT rules

PlWiki Prolog Engine

DokuWiki plwiki render render

PHP stack

plwiki syntax lexer wiki files SWI

Prolog

Prolog files

Apache Web Server

Unix Filesystem

Categories, relations, attributes and queries are represented by appropriate

Prolog terms. Technically, SMW markup is converted to Prolog code and then saved in a Loki le related to a Wiki page. Examples (annotations written on a page for "The Call of Cthulhu" book) are as follows, with the SMW syntax given rst, and the Prolog representation below. [[category:book]]

wiki_category(’book’,’the_call_of_cthulhu’). **Author**: [[author::h_p_lovecraft]]

wiki_relation(’the_call_of_cthulhu’,’author’,’h_p_lovecraft’). **Date**: [[date:=2011]]

wiki_attribute(’the_call_of_cthulhu’,’date’,’2011’). {{#ask: [[category:book]] [[author::h_p_lovecraft]]}} wiki_category(’book’,Page), wiki_relation(Page,’author’,’h_p_lovecraft’).

Semantic Web Standards Support RDF annotations can be embedded directly

in the XML serialization. They are parsed by the SWI-Prolog semweb/rdf_db library, and turned to the internal representation. Within the wikitext, a SPARQL query (SELECT, ASK or DESCRIBE) may be posed. The query scope is the whole wiki system. Analogously to the SMW-like queries, SPARQL ones are also translated to Prolog goals and then executed by the wiki engine.

Semantic information gathered in Loki may be exported to the RDF/XML format. The exported le consists of a header with used namespaces, metadata of the exported page, and optionally ontological information about categories, relations and attributes. Categories are exported as OWL Classes, relations between pages as Object Properties, and attributes as Datatype Properties. Information about subcategories and subproperties is exported with the the use of rdfs:subClassOf and rdfs:subProperty .

Rule-based Reasoning An optional rule layer is provided using the HeaRT [3] run

time for the XTT2 framework [ 6 ]. XTT2 (eXtended Tabular Trees v2) knowledge representation uses attributive table format. Rules based on the same attributes are grouped within tables, and the system is split into a network of such tables representing the inference ow. XTT2 rules can be serialized into a HMR (HeKatE Meta Representation) format, supported in Loki.

An example rule: xrule a/1: [age in[18to100],movie_types sim[comedy]]==> [age_filter set union(age_filter,[adult_comedy])]:comedy_rules. would be interpreted as: for users who are older than 18 and like comedies adjust the age_lter attribute and redirect the inference to comedy_rules table.

HeaRT (HeKatE RunTime), a dedicated inference engine for the XTT2 rule

bases, has been added to Loki as a part of the plugin responsible for parsing

Prolog. HMR code is embedded on wiki pages within the <pl></pl> tags (see

Fig. 2). To run reasoning, a <pl scope="" goal=""> tag is used. If the goal is a valid HeaRT command, the reasoning is performed by the engine, the result is calculated and rendered on a wiki page. Embedding HeaRT in Loki is currently in an experimental phase and is not provided with the current release.

Summary

In the paper, a semantic wiki called Loki has been presented. An essential feature

of the system is a strong rule-based reasoning thanks to a coherent knowledge representation. In the system, standard semantic annotations are mapped to the

Prolog knowledge base, in which also rule-based reasoning is specied. Moreover,

a custom rule-based engine using decision tables and trees is provided. Loki allows for the development of modularized knowledge bases with the use of a wiki.

In future, Loki is planned to be used as a platform for knowledge evaluation [1].

References

1. Baumeister , J. , Nalepa , G.J.: Verication of distributed knowledge in semantic knowledge wikis . In: Lane, H.C. , Guesgen , H.W. (eds.) FLAIRS-22 : Proceedings of the twenty-second international Florida Articial Intelligence Research Society conference: 1921 May 2009 , Sanibel Island , Florida, USA. pp. 384389 . FLAIRS, AAAI Press, Menlo Park, California ( 2009 )

2. Nalepa , G.J.: PlWiki a generic semantic wiki architecture . In: Nguyen, N.T. , Kowalczyk , R. , Chen , S.M. (eds.) Computational Collective Intelligence. Semantic Web, Social Networks and Multiagent Systems , First International Conference, ICCCI 2009, Wroclaw, Poland, October 5- 7 , 2009 . Proceedings. Lecture Notes in Computer Science , vol. 5796 , pp. 345356 . Springer ( 2009 )

3. Nalepa , G.J.: Architecture of the HeaRT hybrid rule engine . In: Rutkowski, L. , [et al. ] (eds.) Articial Intelligence and Soft Computing: 10th International Conference , ICAISC 2010: Zakopane, Poland, June 1317, 2010 , Pt. II. Lecture Notes in Articial Intelligence , vol. 6114 , pp. 598605 . Springer ( 2010 )

4. Nalepa , G.J.: Collective knowledge engineering with semantic wikis . Journal of Universal Computer Science 16 ( 7 ), 10061023 ( 2010 )

5. Nalepa , G.J.: Loki semantic wiki with logical knowledge representation . In: Nguyen, N.T. (ed.) Transactions on Computational Collective Intelligence III, Lecture Notes in Computer Science , vol. 6560 , pp. 96114 . Springer ( 2011 )

6. Nalepa , G.J. , Ligƒza , A. : HeKatE methodology, hybrid engineering of intelligent systems . International Journal of Applied Mathematics and Computer Science 20 ( 1 ), 3553 ( 2010 )