=Paper=
{{Paper
|id=None
|storemode=property
|title=tFacet: Hierarchical Faceted Exploration of Semantic Data Using Well-Known Interaction Concepts
|pdfUrl=https://ceur-ws.org/Vol-817/paper3.pdf
|volume=Vol-817
|dblpUrl=https://dblp.org/rec/conf/interact/BrunkH11
}}
==tFacet: Hierarchical Faceted Exploration of Semantic Data Using Well-Known Interaction Concepts==
https://ceur-ws.org/Vol-817/paper3.pdf
tFacet: Hierarchical Faceted Exploration of Semantic
Data Using Well-Known Interaction Concepts
Sören Brunk1 and Philipp Heim2
1
Digital Enterprise Research Institute, National University of Ireland, Galway
soren.brunk@deri.org
2
Institute for Visualization and Interactive Systems (VIS),
University of Stuttgart, Germany
philipp.heim@vis.uni-stuttgart.de
Abstract. Information stored in the Semantic Web is becoming more and more
interesting for average Web users. Due to the complexity of existing tools,
however, accessing it is difficult. In this paper we therefore introduce tFacet, a
tool that uses well-known interaction concepts to enable hierarchical faceted
exploration of semantic data for non-experts. The aim is to facilitate the
formulation of semantically unambiguous queries to allow a faster and more
precise access to information in the Semantic Web for the broader public.
Keywords: Faceted exploration, faceted search, Semantic Web, known
interaction concepts, hierarchical facets.
1 Introduction
The amount of information available as semantic data is growing rapidly. As of June
2011, the Linking Open Data (LOD) cloud [1], for instance, contained more than 200
different datasets. The most popular dataset within the LOD cloud is the DBpedia
dataset [2]. It contains structured information that is extracted from Wikipedia articles
and converted into a semantic representation. It is publicly accessible via the SPARQL
[3] query language, allowing for semantically unambiguous access. In comparison to
the often ambiguous text search, it allows the formulation of more complicated
requests accurately and thus supports targeted and quick access to information.
A disadvantage of using SPARQL is, however, that users have to learn the
language first in order to access information through SPARQL queries; making it
rather a language for experts. In order to meet the needs of all users, a simpler user
interface is required to create semantically unambiguous and complex queries without
the need to learn the complex syntax of a query language. One approach to solve this
problem is based on the concept of faceted exploration [4]. In faceted exploration, the
user always sees all remaining search options within the search process and can select
them step-by-step in order to refine the query.
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tFacet: Hierarchical Faceted Exploration of Semantic Data
Several applications exist that implement the concept of faceted exploration in
order to allow users to access semantic data. Examples are mSpace [5], Parallax [6],
Faceted Wikipedia Search [7] or gFacet [8]. Most existing applications, however,
don’t use the full potential of faceted exploration in combination with semantic data
and thus lack the ability to create powerful queries. Others allow the creation of more
complex queries but are often difficult to use. mSpace and Faceted Wikipedia Search,
for example, are easy to use, but they don’t support the creation of hierarchical facets;
that is, facets that are connected to the results through indirect attributes. In contrast,
Parallax and gFacet do support hierarchical facets. However, the creation of those can
be difficult for inexperienced users due to the use of new and unfamiliar interaction
concepts within these tools.
For that reason we introduce tFacet, a tool that uses well-known interaction
concepts in order to make the power of faceted exploration available also for
inexperienced users.
2 tFacet
tFacet, like the other tools, uses the concept of faceted exploration to access semantic
data. However, it thereby applies interaction concepts that are well-known from other
applications and thus allows the widespread use of already existing knowledge in the
formulation of semantically unique queries. It is implemented using the Adobe Flex
Framework [9] and therefore runs in any Web Browser with the Flash plugin. Using
SPARQL as the query language allows for faceted exploration of any RDF dataset
accessible via a SPARQL endpoint. By default tFacet uses the DBpedia dataset but
can be easily configured to access other datasets as well.
2.1 Initial Search Space Limitation
Each exploration within tFacet starts with an initial limitation of the search space.
This step is necessary to reduce the number of possible results as well as the number
of facets to a displayable amount. The user selects a base result class from a tree
representation of all classes contained in the dataset. The better the user knows what
he is looking for, the more precisely he can restrict the search space. For example in
the DBpedia Ontology he could select “Eurovision song contest entry” as a very
specific base class limiting the search space to 1054 objects. On the other hand, if he
is not able to specify his search goal in detail in advance, he could choose a more
abstract base class such as “film”; containing 53619 objects (see Figure 1).
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tFacet: Hierarchical Faceted Exploration of Semantic Data
Fig. 1. Selection of base class “film” from the DBpedia ontology.
2.2 Hierarchical Faceted Exploration
By pre-selecting a base class, the exploration is limited to objects of that class. Thus
in Figure 2 only objects of the class “film” are displayed in the result set (A). On the
left side a directory tree representation of facets is shown. It displays all facets that
can be used to filter objects in the result set. At first, only the top hierarchy of the tree
is visible, containing all facets related to direct attributes of the result set. In case of
films, for instance, it contains facets such as directors or actors of the corresponding
movies. In addition, some elements of the tree can be expanded in order to show
lower hierarchy levels with additional facets. Those facets refer to indirect attributes
of the result set. For movies these could be, for example, the birthplace of the director
of the movie.
The user now can select individual facets from the tree to show the facet’s detail
view in the right area (Figure 2, C). Facets in the detail view are arranged vertically
and always contain all remaining search options as selectable attributes to explore or
filter the result set. By selecting individual attribute values, the result set is reduced to
objects having that value. For instance, by selecting a director, the result set is filtered
to show only movies from that director. Attributes in different facets are combined
using the AND-operator while attributes within one facet are combined using the OR-
operator. In this manner, the result set can be refined iteratively until the information
wanted has been found.
33
tFacet: Hierarchical Faceted Exploration of Semantic Data
Fig. 2. The main view of tFacet is divided into three parts: Result set (A), facet tree (B) and
facet details (C). Columns can be added interactively (D).
In addition to the result set, a filter operation also updates all other facets that are
shown in the detail view. All attributes that would lead to an empty result set when
selected are hidden. Furthermore, the expected number of results when selecting a
certain attribute is shown in brackets besides this attribute. This feature helps to avoid
dead-ends and allows a user to estimate the outcome of a specific filter operation.
All facets available in the directory tree can be extracted automatically from
semantic data by using SPARQL queries. All properties of the selected base class are
collected and displayed in the tree. If a property leads to a literal this is represented by
a document symbol in the tree and cannot be further explored (see “release date” in
Figure 2, B). If a property leads to objects of another ontological class it is
represented by a directory symbol and can be further explored (see “director: Person”
in Figure 2, B). The name of such a sub-directory is composed of two components:
(1) the type of the property (here “director”) and (2) the class of the objects (here
“Person”). Representing object properties as sub-trees allows also deeply nested
information to be used for faceted exploration. In this way, the birthplaces of the
directors of the movies in the result set can be used as hierarchical facet to show, for
example, only movies that were directed by directors born in Stuttgart (Figure 2, C).
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tFacet: Hierarchical Faceted Exploration of Semantic Data
2.3 Additional Columns
Until now we have used the linked structure of the Semantic Web only for faceted
exploration. It is also possible to use this structure to enhance the presentation of the
result set by additional details. To demonstrate this, tFacet implements a functionality
that allows users to add additional columns to both the result set as well as the facets
and also to use those columns for sorting.
In order to add an additional column, the user can click the button "Visible
Properties" to see all properties and choose the ones that should be visible in the list
(Fig. 2, D). For example, in this way it is possible to use information about the actors
of a movie ("Starring") both to filter and sort the result set. Furthermore, having the
properties available as additional columns allows the relations between information to
be directly visible for the user (e.g. the relations between movies and actors) in
contrast to the separated representation via facets.
But often there is more than one value for a property (e.g. usually more than one
actor plays in a movie). In that case, the current implementation of tFacet uses a
simple list to display multiple values. This can cause problems however, if many
values exist for a property, for example, if a movie has many actors. To avoid this
problem an abbreviated list could be shown initially or just the number of entries,
with the possibility to expand the view if necessary. With numerical data it would also
be possible to show an aggregated view.
In general, the idea of additional columns is not only limited to direct properties,
but can be implemented also for indirectly related properties. For that, one could
imagine displaying a directory tree like in Fig. 2 D to select information only
connected indirectly. However, one problem with such an implementation would be
how to maintain the clarity of the presentation as many trees and their hierarchical
directory structures could confuse the user more than help him create search requests.
2.4 Well-known interaction concepts
tFacet uses several interaction concepts that are known from common applications in
order to ease the use of faceted exploration. The most important ones are:
x Directory tree: In many applications, directory trees are used for the navigation in
and the management of hierarchical data. A logical conclusion was therefore the
representation of hierarchical facets in a directory tree within tFacet. Like in
popular file managers, nodes shown as folder symbol can be explored further while
nodes shown as file symbol represent a leaf node.
x Subdivision of the user interface into three parts: Also, a partitioning of the user
interface into an overview (directory tree), a detailed view (right pane) and a result
view is frequently used. The possibility to show multiple detail views (in this case
facets) at the same time is not widespread, for the definition of filters in more than
one facet, however, necessary.
x Organization into columns: In many grid-based applications (for example, in
Windows or Mac OS applications) the user can determine individually, which
columns are of interest for him and have these displayed. In a similar way in tFacet
35
tFacet: Hierarchical Faceted Exploration of Semantic Data
he can display a menu of all properties he might be interested in and add or remove
individual columns. The same is true for sorting by individual columns by clicking
on the column header.
3 Summary and Future Work
In this paper, we proposed tFacet, a new application to enable all users to create
semantically unambiguous search requests using the concept of faceted exploration.
The aim was to enable the full potential of this concept by keeping its usage as simple
as possible through the use of well-known interaction concepts. Through the use of a
directory tree even remote information can be included in the query as hierarchical
facets and the possibility to show connected properties in additional columns
facilitates control over the level of detail of the information displayed.
Thus, tFacet offers interesting approaches to make the potential of semantic data
accessible for everyone. A key part of this is the strategy to transfer already known
concepts into the specific interaction environment of the Semantic Web.
In the future we plan further development of tFacet to make its usage even simpler.
For example, data-specific visualizations, such as sliders or maps could be used to
ease the creation of queries and improve the presentation of results. An integration of
the approaches discussed in Section 2.3 to extend the columns functionality to use
hierarchical properties could be useful for a consistent and powerful implementation
of this concept. Furthermore, an evaluation of the user interface would be helpful,
especially to see if the use of known interaction concepts can help users to reach their
goal faster. Including a comparison to similar tasks and tools in order to measure
empirically, whether the intended goal of tFacet, a simplified usage, has been
achieved.
References
1. LOD cloud (2010): http://richard.cyganiak.de/2007/10/lod/lod-datasets_2010-09-22.html
2. Auer, S.; Bizer, C.; Kobilarov, G.; Lehmann, J.; Cyganiak, R.; Ives, Z.: DBpedia: A Nucleus
for a Web of Open Data. In: Proc. of the 6th ISWC 2008, 2008, pp. 722-735.
3. SPARQL (2008): http://www.w3.org/TR/rdf-sparql-query/
4. Yee, K.-P.; Swearingen, K.; Li, K.; Hearst, M.: Faceted metadata for image search and
browsing. In: Proc. of the CHI 2003, ACM Press, 2003; pp. 401-408.
5. Schraefel, m.c.; Smith, D.; Owens, A.; Russell, A.; Harris, C.; Wilson, M.: The evolving
mSpace platform: leveraging the semantic web on the trail of the memex. In: Proc. of
Hypertext 2005, ACM Press, 2005; pp. 174-183.
6. Huynh, D. and Karger, D.: Parallax and companion: Set-based browsing for the Data Web
(2009). http://davidhuynh.net/media/papers/2009/www2009-parallax.pdf
7. Hahn, R.; Bizer, C.; Sahnwaldt, C.; Herta, C.; Robinson, S.; Bürgle, M.; Düwiger, H.;
Scheel, U.: Faceted Wikipedia Search. In: Proc. of BIS 2010, pp. 1-11.
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Proc. of the 7th Extended Semantic Web Conference (ESWC2010), Part I, Springer, 2010,
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9. Adobe Flex (2011): http://www.adobe.com/de/products/flex/
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