In this paper we present an ontology-based query expansion widget which utilizes the ontologies published in the ONKI Ontology Service. The widget can be integrated into a web page, e.g. a search system of a museum catalogue, enhancing the page by providing a query expansion functionality. We have tested the system with general, domainspeci c and spatio-temporal ontologies.
In information retrieval systems the relevancy of search results depends on the
user's ability to represent her information needs in a query [
We have implemented a web widget providing query expansion functionality
to web-based systems as an easily integrable service with no need to change
the underlying system. The widget uses ontologies to expand the query terms
with semantically related concepts. The widget extends the previously
developed ONKI Selector widget, which is used for selecting concepts especially for
annotation purposes [
The user does not have to be familiar with the ontologies used in content
annotations by utilizing the autocompletion search feature of the widget, as the
system suggests matching concepts as the user is writing the query string. Also,
to help the user to disambiguate concepts the ONKI Ontology Browsers [
The query expansion widget supports Semantic web and legacy systems1,
i.e. either the concept URIs or the concept labels can be used in queries. In
1 By legacy systems we mean systems that do not use URIs as identi ers.
legacy systems cross-language search can be performed, if the used ontology
contains concept labels in several languages. In addition to the widget, the query
expansion service can also be utilized via JavaScript and Web Service APIs. The
query expansion widget and the APIs are available for public use as part of
the ONKI Ontology Service2 [
The contribution of this paper is to present an approach to perform query expansion in systems cost-e ectively, not to evaluate how the chosen query expansion methods improve information retrieval in the systems. 2
The ONKI query expansion widget can be used with any ontology published in the ONKI Ontology Service. The service contains some 60 ontologies at the time of writing. Users are encouraged to submit their own ontologies to be published in the service by using the Your ONKI Service4. In the following, we describe how we have used di erent types of ontologies for query expansion. 2.1
Query Expansion with General and Domain-speci c Ontologies
For expanding general and domain-speci c concepts in queries we have used The
Finnish Collaborative Holistic Ontology KOKO5 which consists of The Finnish
General Upper Ontology YSO [
Using other relations in addition or instead of the is-a relation in query
expansion might be bene cial. When considering general associative relations, caution
should be exercised as their use in query expansion can lead to uncontrolled
expansion of result sets, and thus to potential loss in precision [
2.2
Query Expansion with the Spatio-temporal Ontology SAPO
A spatial query can explicitly contain spatial terms (e.g. Helsinki) and spatial
relations (e.g. near), but implicitly it can include even more spatial terms that
could be used in query expansion [
In SAPO regional overlap mappings are expressed as depicted in Figure 1,
where example Turtle RDF7 statements8 express that the region of the latest
temporal part of place sapo:Joensuu | i.e. the one valid from the beginning of
year 2009 | overlaps the region of the temporal part of sapo:Eno of years 1871{
2008. The temporal part of the place simply means the place during a certain
time-period such that di erent temporal parts might have di erent extensions
(i.e. borders) [
sapo:Joensuu(2009-) sapo:begin
"2009-01-01" ; sapo:overlaps sapo:Eno(1871-2008) , sapo:Pyhaselka(1925-2008) , sapo:Joensuu(2005-2008) .
Fig. 2. A place is a union of its temporal parts. Moreover, places may have overlapped other places at some time.
For example, the place sapo:Joensuu is a union of four temporal parts, de ned in the example depicted in Figure 2. However, annotations of items likely utilize places rather than their temporal parts. For this reason the model uses property sapo:overlapsAtSomeTime to explicate that e.g. a place sapo:Joensuu has | at some point in the history | overlapped together ve di erent places (sapo:Eno and four others). In other words, e.g. at least one temporal part of sapo:Joensuu has overlapped at least one temporal part of sapo:Eno. We have used this more generic property sapo:overlapsAtSomeTime between places for query expansion.
8 The example uses the following pre x - sapo: http://www.yso. /onto/sapo/
We have created a demonstration search interface9 consisting of the original Kantapuu. search form10 and integrated ONKI widgets for query expansion. Kantapuu. is a web user interface for browsing and searching for collections of Finnish museums of forestry, using simple matching algorithm of free text query terms with the item index terms. The ontologies used in the query expansion are the same ones as used in annotation of the items11, namely The Finnish General Upper Ontology YSO, Ontology for Museum Domain MAO12 and Ag forest Ontology AFO13. For expanding geographical places the Finnish Spatio-temporal Ontology SAPO is used.
When a desired query concept is selected from the results of the autocompletion search of the widget or by using the ONKI Ontology Browser, the concept is expanded. The resulting query expression is the disjunction of the original query concept and the concepts expanding it, formed using the Boolean operation OR. The query expression is placed into a hidden input eld, which is sent to the original Kantapuu. search page when the HTML form is submitted.
An example query is depicted in Figure 3, where the user is interested in old publications from place Joensuu. User has used the autocompletion feature of the widget to input to the keywords eld a query term \publicat", which has been autocompleted to the concept publications, which has been further expanded to its subclasses (their Finnish labels). Similarly, the place Joensuu has been added to the eld place of usage and expanded with the places it overlaps.
The result set of the search contains four items, from which two are magazines used in place Eno and the rest two are cabinets for books used in place Joensuu. Without using the query expansion the result set would have been empty, as the place Eno and the concept books were not in the original query. 4
When implementing the demonstration search interface for the Kantapuu. system with ONKI widgets we faced some challenges. If a query concept has lots of subconcepts, the expanded query string may become inconveniently long, as the concept URIs/labels of the subconcepts are added to the query. This may cause problems because the used HTTP server, database system or other software components may set limits to the length of the query string. With lengthy queries the system may not function properly or the response times of the system may increase.
10 http://www.kantapuu.fi/, follow the navigation link \Kuvahaku". 11 To be precise, the ontologies are based on thesauri that have been used in annotation of the items. 12 http://www.seco.tkk.fi/ontologies/mao/ 13 http://www.seco.tkk.fi/ontologies/afo/
Future work includes user testing for nding out if users consider the query expansion of the concepts and places useful. Also, systematic evaluation of the search systems used would be essential to nd out if the query expansion improves the information retrieval, and speci cally which semantic relations improve the results the most. The user interface of the query expansion widget needs further developing, e.g., the user should be able to select/unselect the suggested query expansion concepts.
We thank Ville Komulainen for his work on the original ONKI server and Leena Paaskoski and Leila Issakainen for cooperation on integrating the ONKI query expansion widgets into the Kantapuu. system. This work has been partially funded by Lusto The Finnish Forest Museum14 and partially by the IST funded EU project SMARTMUSEUM15 (FP7-216923). The work is a part of the National Semantic Web Ontology project in Finland16 (FinnONTO) and its followup project Semantic Web 2.017 (FinnONTO 2.0, 2008-2010), funded mainly by the National Technology and Innovation Agency (Tekes) and a consortium of 38 private, public and non-governmental organizations. 14 http://www.lusto.fi 15 http://smartmuseum.eu/ 16 http://www.seco.tkk.fi/projects/finnonto/ 17 http://www.seco.tkk.fi/projects/sw20/