# Adapting the LodView RDF Browser for
Navigation over the Multilingual
Linguistic Linked Open Data Cloud ††thanks:
Please, cite as: Alexander Kirillovich and Konstantin Nikolaev. Adapting the
LodView RDF Browser for Navigation over the Multilingual Linguistic Linked
Open Data Cloud // Proceedings of the 9th IEEE International Conference on
Sciences of Electronics, Technologies of Information and Telecommunications
(SETIT 2022), Genova, Italy & Sfax, Tunisia, 28-30 May 2022. IEEE, 2022. Pp.
143–149 [revised version]. https://arxiv.org/abs/2208.13295

Alexander Kirillovich  Kazan Federal University,
Joint Supercomputer Center
of the Russian Academy of Sciences
Kazan, Russia
<EMAIL_ADDRESS>Konstantin Nikolaev  Kazan Federal University,
Joint Supercomputer Center
of the Russian Academy of Sciences
Kazan, Russia
<EMAIL_ADDRESS>
###### Abstract

The paper is dedicated to the use of LodView for navigation over the
multilingual Linguistic Linked Open Data cloud. First, we define the class of
Pubby-like tools, that LodView belongs to, and clarify the relation of this
class to the classes of URI dereferenciation tools, RDF browsers and LOD
visualization tools. Second, we reveal several limitations of LodView that
impede its use for the designated purpose, and propose improvements to be made
for fixing these limitations. These improvements are: 1) resolution of
Cyrillic URIs; 2) decoding Cyrillic URIs in Turtle representations of
resources; 3) support of Cyrillic literals; 4) user-friendly URLs for RDF
representations of resources; 5) support of hash URIs; 6) expanding nested
resources; 7) support of RDF collections; 8) pagination of resource property
values; and 9) support of LaTeX math notation. Third, we partially implement
several of the proposed improvements.

###### Index Terms:

LodView, Pubby-class tool, RDF browser, dereferenciation tool, Linked Data
visualization, Linguistic LOD

##  I Introduction

Digital language resources are key to linguistics research and natural
language processing. Among these resources are corpora, thesauri, lexicons,
grammatical dictionaries, valence dictionaries, linguistic data categories
registers, and other.

Publishing linguistic resources according to the principles of Linked Open
Data (LOD) [1, 2, 3] is a recently established trend, that has led to the
emergence of the fast-growing Linguistic Linked Open Data (LLOD) cloud [4, 5].
It offers a number of advantages, including structural and conceptual
interoperability, and integration of heterogeneous linguistic resources to
solve a common problem.

As a part of the global LLOD project we are working on developing the fragment
of the LLOD cloud for Russian and minority languages of Russia. This fragment
integrates several resources such as the RuThes [6], TatThes [7], TatWordNet
[8], TatVerbBank, the Russian corpus “OpenCorpora” [9], the Tatar national
corpus “Tugan Tel” [10, 11, 12], the parallel informal/formal corpus of
educational mathematical texts in Russian [13], the linguistic layer of the
educational mathematical ontology OntoMathEdu [14, 15, 16] and other.

In accordance with Linked Open Data best practices, the integrated resources
have to be available via RDF dumps, SPARQL endpoints and dereferenceable URIs.
For navigation over the LOD cloud via dereferenceable URIs, a specialized tool
is required. One of the most popular navigation tools is the LodView RDF
browser.

Figure 1: The place of Pubby-class tools among other LOD applications. Figure
2: Visualization of the ‘автомобиль’ (‘automobile’) lexical entry in LodView

LodView (https://github.com/dvcama/LodView) is a web application for
dereferencing URIs of the RDF resources stored in the SPARQL-exposed datasets.
When a human user requests the URI of an RDF resource, LodView retrieves
information of the resource in the dataset and visualizes this information as
a human-readable HTML page. On the page, the resource properties are
represented in a tabular form. Each row represents a property-value pair; the
first cell of the row contains the property name and the second contains the
property value or values. If a property value is the URI of an another
resource, this value is rendered as a link. A user may follow the link and get
representation of the another resource, thus navigating over RDF dataset. The
HTML page also contains links to the RDF documents with machine-readable
representation of the resource (in different serialization format, including
N-Triples, Turtle, RDF/XML and JSON-LD). When the URI is requested not by
human but by a software agent, LodView immediately returns the machine-
readable RDF representation.

Fig. 1. shows the place of LodView among other LOD applications.

Fig. 2 represents an example how LodView visualizes the ‘автомобиль’
(‘automobile’) lexical entry.

However, LodView has several limitations that impede its use for navigation
over the multilingual LLOD cloud. In this paper, we continue the work
initiated in [17, 18] and present the first version of our LodView fork,
adapted to address these limitations.

The rest of the paper is organized as following. In Section 2 we define the
class of Pubby-like tools that LodView belongs to and outline the
relationships of this class with other classes of LOD applications. In Section
3 we list the limitations of LodViews and propose improvements to be made for
fixing these limitations. Section 4 describes the improvements, that have
already been made by us. In Conclusion, we outline the directions of future
work.

##  II Related Works

In this section we clarify the place of LodView among other LOD applications.

LodView belongs to a class of tools, that we called the Pubby class after its
first prominent representative. We define a Pubby-class tool as a LOD
application which is:

  1. 1.

a URI dereferenciation tool, i.e. when a client requests the URI of an RDF
resource via HTTP protocol, the tool handles the request and responds with a
resource representation;

  2. 2.

a LOD visualization tool, i.e. it represents the resource in human-friendly
visual form;

  3. 3.

a Linked Data or RDF browser, i.e. it allows a user to navigate between RDF
resources of an RDF dataset or the entire LOD cloud, by following links in
resource representations;

  4. 4.

and a SPARQL endpoint interface, i.e. it retrieves information about resources
from a SPARQL-exposed dataset.

Conceptually, these four classes are independent and so it is possible for
example to conceive a URI dereferenciation tool that doesn’t allow a user to
follow links or even doesn’t visualize a resource at all, dereferencing it
just as a source RDF file in some textual serialization format. However, in
practice, every known URI dereferenciation tool is an RDF browser, and every
known RDF browser is a LOD visualization tool (see the relationships between
the classes at Fig. 1).

Pubby-class tools. Besides LodView, the Pubby class includes the following
tools:

  * •

Pubby111http://wifo5-03.informatik.uni-mannheim.de/pubby/. A Java web
application. Was used for publishing a lot of LOD datasets, including DBpedia.
However, it hadn’t been updated in more then 10 years and now its GitHub
repository is officially archived.

  * •

LODDY222https://bitbucket.org/art-uniroma2/loddy/src/master/. A Java web
application. Is used for publishing the AGROVOC Linked Dataset.

  * •

Zazuko Trifid333https://github.com/zazuko/trifid. A Node.js-based web
application. Is used in two open data platforms of Swiss Confederation.

  * •

RDFBrowser444https://github.com/okgreece/RDFBrowser. A PHP web application. Is
used by the OpenBudgets.eu platform.

  * •

LODI555https://github.com/marfersel/LODI. A Node.js-based web application. Is
used by two Spanish open data portals.

Other Linked Data and RDF browsers. While almost all Pubby-class tools are
Linked Data browsers, there are Linked Data browsers that are not Pubby-class
tools. Among the first such Linked Data browsers the well-known ones are
Haystack [19], Disco666http://wifo5-03.informatik.uni-
mannheim.de/bizer/ng4j/disco/ and
Tabulator777https://github.com/linkeddata/tabulator [20]. Examples of the more
recent developments are Phuzzy.link888https://github.com/blake-
regalia/phuzzy.link [21] and
RDFSurveyor999https://github.com/guiveg/rdfsurveyor [22].

Besides Linked Data browsers, there are many LOD visualization tools of
several other types, including graph-based and ontology visualization tools.

Graph-based visualization tools. While RDF browsers mainly work on the level
of single RDF resources, graph-based tools work on the level of entire RDF
graphs. One of the earliest tools in this category is
IsaViz101010https://www.w3.org/2001/11/IsaViz/, a desktop application for
authoring and visualizing RDF models, represented as relatively small local
RDF files. In contrast, graphVizdb111111http://www.graphvizdb.com/ [23]
enables the user to navigate over very-large RDF graphs.
LodLive121212https://github.com/LodLive/LodLive [24] and
LODmilla131313https://github.com/dsd-sztaki-hu/LODmilla-frontend [25, 26]
provide incremental graph visualization.
RelFinder141414http://www.visualdataweb.org/relfinder.php [27] and
WiSP151515https://github.com/GTartari/Weighted-Shortest-Paths [28] are
intended to identify and visualize the paths between two selected RDF
resources.

Ontology visualization tools. Examples of these tools are OWLPropViz,
WebVOWL161616https://github.com/VisualDataWeb/WebVOWL [29] and
OWLGrEd171717http://owlgred.lumii.lv/ [30].

For a book length overview of LOD visualization tools, we refer the interested
reader to [31].

##  III Required improvements of LodView

In this section, we list the limitations of LodViews and propose improvements
to be made to fix these limitations.

Figure 3: Error occurred while resolving a URI that contains Cyrillic
characters.

1) Resolution of Cyrillic URIs. In a LLOD dataset, the URI of an RDF resource
may contain Cyrillic characters. For example, in the RuThes Cloud dataset, the
URI of the lexical entry ‘машина’ (‘car’) is
<http://lod.ruthes.org/resource/entry/RU-мaшинa-n>. However, in some
environments, resolving Cyrillic URIs by LodView leads to an error (see Fig.
3). LodView must resolve Cyrillic URIs in all environments.

2) Decoding Cyrillic URIs in Turtle representations of resources. In a
machine-readable RDF representation of a resource in the Turtle serialization
format, Cyrillic URIs are presented in an encoded form. Fig. 4A shows a
fragment of the Turtle representation of the Automobile concept, that contains
encoded URIs. Encoded URIs hinder readability of Turtle documents. In the
Turtle representation of a resource, URIs must be presented in a decoded form
(for example, as in Fig. 4B).

Figure 4: Fragment of a Turtle representation of a resource with encoded and
decoded URIs.

3) Support of Cyrillic literals. In a machine-readable RDF representation of a
resource, Cyrillic literals are in broken encoding. This happens even if the
dataset was encoded by Unicode. Fig. 5A shows a Turtle representation of the
RuThes Cloud resource, that contains literals in broken encoding. LodView must
represent Cyrillic literals correctly (as in Fig. 5B).

Figure 5: Fragment of a Turtle representation of a resource with broken and
recovered literals.

4) User-friendly URLs for RDF representations of resources. LodView resolves
URI’s of RDF resources in accordance with the content negotiation principle.
When the URI of an RDF resource is requested on by a human user, LodView
redirects the user to the URL of the HTML page with human-readable resource
representation. When the URI is requested by a software agent, LodView
redirects the agent to the URL of RDF document with the machine-readable
representation.

URLs of HTML pages are of user-friendly format: <RESOURCE_URI.html>. For
example, the resource identified by the URI
<http://lod.ruthes.org/resource/entry/RU-мaшинa-n> is represented by the HTML
document located at the URL <http://lod.ruthes.org/resource/entry/RU-
мaшинa-n.html>. However, URLs of RDF documents are rather cumbersome. For
example, the Turtle representation of the aforementioned resource is located
at the URI <http://lod.ruthes.org/resource/entry/RU-мaшинa-n?output=appli-
cation%2Frdf%2Bxml>. In order the URL’s of RDF documents can be easy to read,
they must be of user-friendly formats: <RESOURCE_URI.ttl>, <RESOURCE_URI.n3>,
etc. For example, the Turtle representation of the
<http://lod.ruthes.org/resource/entry/RU-мaшинa-n> resource must be assigned
the URI <http://lod.ruthes.org/resource/entry/RU-мaшинa-n.ttl>.

5) Support of hash URIs. In LLOD datasets, RDF resources may be identified by
hash URIs. A hash URI is a URI, that contains a special part separated from
the base part of the URI by a hash symbol (#). This special part is called the
‘fragment identifier’. Usually, a hash URI identify a resource, that is
somehow subordinated to the resource identified by the base part of this URI.
For example, in the Princeton WordNet dataset, the hash URI <http://wordnet-
rdf.princeton.edu/wn31/cat-n#CanonicalForm> identifies the canonical form of
the lexical entry ‘cat’, while the lexical entry itself is identified by the
base part <http://wordnet-rdf.princeton.edu/wn31/cat-n>. In this case, the URI
of the canonical form of the lexical unit is formed by the URI of this lexical
entry concatenated with the #CanonicalForm fragment identifier.

However, LodView can’t resolve URIs with fragment identifiers. So, for
example, when a user try to retrieve the hash URI <http://wordnet-
rdf.princeton.edu/wn31/cat-n#CanonicalForm>, LodView sends a representation
not of the resource identified by this URI, but of the resource identified by
the URI <http://wordnet-rdf.princeton.edu/wn31/cat-n>. This problem is caused
by the HTTP protocol: when a client wants to retrieve a hash URI, the HTTP
protocol requires the fragment part to be stripped off before requesting the
URI from the server. This problem can be solved as follows: when LodView
resolves a URI, its response must contain not only information of the
requested resource, but also of all other resources identified by hash URIs
with the same base part. For example, the representation of the resource
identified by <http://wordnet-rdf.princeton.edu/wn31/cat-n> must contain
information of this resource along with information of the resource identified
by the hash URI <http://wordnet-rdf.princeton.edu/wn31/cat-n#CanonicalForm>.

Figure 6: Blank node, located at the bottom of the page.

6) Expanding nested resources. In LodView, the HTML representation of an RDF
resource contains the table with the resource properties. In each row, the
first cell contains the property name, and the second cell contains its value.
The value of a property may be the URI of another, nested, resource. For the
user, the only way to retrieve information about this nested resource is to
follow the link and go to another HTML page. This need to leave the current
page may spoil the user experience. LodView must allow the user to expand
nested resources enabling him or her to see the properties of these resources
without leaving the current page.

When the property value is a blank node, this value is represented in the
table by the surrogate blank node ID. The description of this blank node
itself is located at the bottom of the page. See for example Fig. 6, where a
blank node is a value of the wn:definition property. In order to see
information of the blank node, a user have to scroll the page. Again, LodView
must allow the user to expand nested blank nodes to see its properties in
place without scrolling the page.

7) Support of RDF collections. LLOD datasets may contain RDF collections.
According to the RDF standard, a collection is represented as a low-level list
structure in the RDF graph. When LodView visualize an RDF collection, it
visualizes not the collection itself, but the underlying list structure. This
way of visualizing makes comprehension of the collection difficult. An example
of visualization of the RDF list < <#comp-объект>, <#comp-культурного>,
<#comp-наследия> > is represented at Fig 7. LodView must visualize RDF
collections as a high-level sequence of its members.

Figure 7: Visualization of an RDF collection.

8) Pagination of resource property values. An RDF resource may have an
arbitrary number of values for a particular property. And this number can be
very big. For example, the RuWordNet thesaurus is linked by the lime:entry
property with more than 100 thousand lexical entries. However, LodView tries
to display all these values at once, which can overwhelm the user with the
amount of data, significantly slow down page loading and even cause server
overload. To prevent these negative consequences, LodView must limit the
number of the displayed property values by providing a pagination widget or
just a “Load more” button.

9) Support of LaTeX math notation. LOD datasets may contain literals with math
notation in the LaTeX format. LodView doesn’t render this notation and
visualizes it just as its source LaTeX code (see Fig. 8). LodView must be able
to visualize math notation it the rendered form.

Figure 8: Visualization of math notation without rendering.

##  IV Implementation of the improvements

Currently, we have implemented the improvements ##1–4 and #9, and partially
the improvements #5 and #6.

Issue #1 (Resolution of Cyrillic URIs). After analyzing the source code of
LodView, we found that this problem is related to the fact that the URI text
is represented in the SPARQLEndPoint class in Western ISO-8859-1 encoding.
This problem was solved by adding a single line of code to the specified class
that recodes the URIs from ISO-8859-1 to Unicode:

IRI = new String (URI.getBytes ("ISO-8859-1"), "UTF-8");

After we solved this problem, LodView began to correctly resolve Cyrillic URIs
and generate a web page displaying the corresponding resource when accessing
them. However, after this, we found a new problem: the resource URI is also
displayed incorrectly on the returned web page.

We solved this new problem by performing a similar recoding in the code of the
corresponding web page (resource.jsp).

Issue #3 (Support of Cyrillic literals). This problem was solved in the same
way as the previous one, using a similar recoding.

Issue #2 (Decoding Cyrillic URIs in Turtle representations of resources). To
solve this problem, we have made changes to the ResourceBuilder class.

Issue #4 (User-friendly URLs for RDF representations of resources). To solve
this problem, we added support for such URLs by making changes to the
ResourceController class.

Issue #6 (Expanding nested resources). The problem was solved as follows. Near
URIs of the nested resources, we added “Expand” buttons. When the user clicks
on this button, an iframe with the representation of this nested resource is
appended just near its URI (see Fig. 9). Also, we are going to implement more
flexible solution, that doesn’t use an iframe.

Figure 9: Example of deploying an embedded resource using an iframe.

Figure 10: Blank node, located in the cell with the property value.

The descriptions of blank nodes are simply moved from the bottom of the HTML
page to the cells with the IDs of the these nodes. For example, Fig. 10
represents the cat synset. For this synset, the value of the wn:definition
property is a blank node. This blank node is represented not only by its ID,
but also by its description, i.e. a table of its own properties.

Issue #9 (Support of LaTeX math notation). In order to solve this problem, we
have developed a special plugin, based on the well-known MathJax
library181818https://www.mathjax.org/ [32] (see Fig. 11).

Figure 11: Visualization of math notation with rendering.

##  V Conclusion

We reveal several limitations of LodView that impede its use for navigation
over the multilingual Linguistic Linked Open Data cloud. For fixing these
limitations, we propose the following improvements: 1) resolution of Cyrillic
URIs; 2) decoding Cyrillic URIs in Turtle representations of resources; 3)
support of Cyrillic literals; 4) user-friendly URLs for RDF representations of
resources; 5) support of hash URIs; 6) expanding nested resources; 7) support
of RDF collections; 8) pagination of resource property values; and 9) support
of LaTeX math notation.

At the moment, we have implemented the improvements ##1–4 and #9, and
partially the improvements #5 and #6. Our fork of LodView is available on
GitHub: https://github.com/ManlyMan1/LodView_Cyrillic.

Currently, we are working on the remaining issues. After that, we are going to
send a pull request to the main LodView repository.

Acknowledgment. The work was initiated for navigation over LLOD cloud at KFU
where was funded by RSF according to the project no. 19-71-10056, and then
adapted for navigation over specialized LaTeX-based math collections at JSC
RAS.

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