=Paper=
{{Paper
|id=None
|storemode=property
|title=Loki - Presentation of Logic-based Semantic Wiki
|pdfUrl=https://ceur-ws.org/Vol-805/kese7-07.pdf
|volume=Vol-805
}}
==Loki - Presentation of Logic-based Semantic Wiki==
https://ceur-ws.org/Vol-805/kese7-07.pdf
Loki Presentation of Logic-based Semantic Wiki
Weronika T. Adrian, Grzegorz J. Nalepa
AGH University of Science and Technology,
al. A. Mickiewicza 30, 30-059 Krakow, Poland
{wta,gjn}@agh.edu.pl
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 seman-
tic 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.
1 Motivation
Semantic wikis enrich standard wikis with the semantic information expressed
by a number of mechanisms. Three basic questions every semantic wiki needs to
address are1 : 1) how to annotate content?, 2) how to formally represent content?,
3) how to navigate content? In last several years multiple implementations of
semantic wikis have been developed, including IkeWiki2 , OntoWiki3 , Semantic
MediaWiki4 , and AceWiki5 . The summary of semantic wiki systems is available6 .
From the knowledge engineering point of view, simply expressing semantics
is not enough. A knowledge-based system should provide both eective knowl-
edge representation and processing methods. In order to extend semantic wikis to
knowledge-based systems, ideas to use rule-based reasoning and problem-solving
knowledge have been introduced. An example of such a system is the KnowWE
semantic wiki7 .The system allows for introducing knowledge expressed with de-
cision rules and trees related to the domain ontology.
Logic-based Wiki [5], or Loki for short, uses the logic programming paradigm
to represent knowledge in the wiki. The main design principles are as follows:
1) provide an expressive underlying logical representation for semantic annota-
tions and rules, 2) allow for strong reasoning support in the wiki, 3) preserve
backward compatibility with existing wikis, namely Semantic MediaWiki.
1
See http://aran.library.nuigalway.ie/xmlui/handle/10379/574.
2
See http://ikewiki.salzburgresearch.at/.
3
See http://ontowiki.net/Projects/OntoWiki.
4
See http://semantic-mediawiki.org/wiki/Semantic_MediaWiki.
5
See http://attempto.ifi.uzh.ch/acewiki/.
6
See http://semanticweb.org/wiki/Semantic_Wiki_State_Of_The_Art.
7
See www.is.informatik.uni-wuerzburg.de/en/research/applications/knowwe.
2 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 imple-
menting a new one, an extension of the DokuWiki8 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.
wikitext
OWL
+ Prolog
wikitext
XTT
RDF
rules
plain
PlWiki Prolog Engine
DokuWiki plwiki plwiki
render syntax SWI
render lexer
Prolog
PHP stack wiki Prolog
files files
Apache Web Server Unix Filesystem
Fig. 1. Loki Architecture PlWiki Implementation
3 Features
The main idea of Loki consists in representing the semantic annotations in a
formalized way, and simultaneously enriching them with an expressive rule-based
knowledge representation. Both semantic annotations and Prolog clauses (facts
and rules) may be embedded within in the wiki content. The resulting knowledge
base is homogeneous from the logical point of view.
SMW Support There are three main methods of semantic annotations in Se-
mantic MediaWiki (SMW) that are supported in Loki: categories, relations and
attributes. Loki also supports the query language used in SMW.
8
See http://www.dokuwiki.org.
2
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 li-
brary, 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 be-
tween pages as Object Properties, and attributes as Datatype Properties. Infor-
mation 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 ta-
bles 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 in-
terpreted 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 tags (see
Fig. 2). To run reasoning, a 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.
3
Fig. 2. Goal query on user pro le page
4 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 speci ed. 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].
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