=Paper=
{{Paper
|id=Vol-485/paper-9
|storemode=property
|title=New Generation of Social Networks Based on Semantic Web Technologies
|pdfUrl=https://ceur-ws.org/Vol-485/paper9-F.pdf
|volume=Vol-485
|dblpUrl=https://dblp.org/rec/conf/um/RazmeritaJF09
}}
==New Generation of Social Networks Based on Semantic Web Technologies==
https://ceur-ws.org/Vol-485/paper9-F.pdf
Workshop on Adaptation and Personalization for Web 2.0, UMAP'09, June 22-26, 2009
New Generation of Social Networks Based on Semantic
Web Technologies: the Importance of Social Data
Portability
Liana Razmerita1, Martynas Jusevičius2, Rokas Firantas2
Copenhagen Business School, Denmark1
IT University of Copenhagen, Copenhagen, Denmark2
liana.razmerita@cbs.dk, martynas@itu.dk, rokas@itu.dk
Abstract. This article investigates several well-known social network
applications such as Last.fm, Flickr and identifies social data portability as one
of the main technical issues that need to be addressed in the future. We argue
that this issue can be addressed by building social networks as Semantic Web
applications with FOAF, SIOC, and Linked Data technologies, and prove it by
implementing a prototype application using Java and core Semantic Web
standards. Furthermore, the developed prototype shows how features from
semantic websites such as Freebase and DBpedia can be reused in social
applications and lead to more relevant content and stronger social connections.
1 Introduction
Social networking sites are developing at a very fast pace, attracting more and more
users. Their application domain can be music sharing, photos sharing, videos sharing,
bookmarks sharing, professional networks, and others. Despite their tremendous
success social networking websites have a number of limitations that are identified
and discussed within this article. Most of the social networking applications are
“walled websites” and the “online communities are like islands in a sea”[1]. Lack of
interoperability between data in different social networks applications limits access to
relevant content available on different social networking sites, and limits the
integration and reuse of available data and information. This may result in a growing
dissatisfaction of the user community and a reduced usability of the websites. More
research combining social networks and Semantic web is required to address the
above mentioned limitations. Research combining social networks and Semantic Web
is an interdisciplinary field, atracting researchers from both social and information
sciences. Current research is mostly related to extraction of semantic data from
existing social applications, its representation and its analysis. For example, there is
work done in extracting ontologies from user contributed folksonomies (collaborative
tagging systems) and integrating ontologies together with folksonomies [2, 3]. Others
propose approaches to development and evolution of lightweight ontologies in a
similar collaborative way [4, 5]. Researchers seem to agree that folksonomies and
(lightweight) ontologies share more common properties than differences and will be
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further integrated, and thus community-based bottom-up development approach will
prevail over top-down controlled engineering efforts.
Much of the current research for representing simple user profiles is based on the
Friend of a Friend (FOAF) project1 – a project aimed at “creating a Web of machine-
readable pages describing people, the links between them and the things they create
and do”. FOAF is currently an important source of RDF data available on the Web
which has already been used for social network analysis [6-8].
A related initiative is Semantically-Interlinked Online Communities (SIOC) project2,
which provides an ontology for describing items and relationships from Internet
discussion methods (such as blogs, forums, and mailing lists) to facilitate
interconnection of these methods via publishing of metadata [9, 10]. Many recent
papers show growing interest in portability issues among social network applications
– they are being called “fundamental problems”, and semantic technologies (mainly
FOAF) are being proposed to solve them [11].
There is theoretical work done combining Semantic Web (SW) and social networks,
especially in analysis of social networks and extraction of knowledge [12]. However,
creation of new end-user semantic social applications as well as their design and
implementation are not well explored. Existing social network applications do not
employ SW technologies, although most of the standards infrastructure is already in
place. Most of them are “walled” websites, which provide limited means for users and
developers to control, publish, and access social data. This limits possibilities for
reuse and integration, which are the driving forces behind Web 2.0 as well as
Semantic Web, and results in growing dissatisfaction in the user community.
This article proves through the implementation of a prototype that Semantic Web
technologies can be used to build a next generation of social networks that overcome
limitations of social networks applications and enable new features currently not
exploited by them.
2 Study of Social Networks
We analyzed applications which we personally use and which we think reflect the
current state of the art in social networking: Last.fm, Flickr, Facebook, LinkedIn.
These social networking applications have a number of technological limitations as
summarized bellow:
• It is not possible to export/import profile data from one application into another
• It is not possible to export/import social relationships from one application into
another
• There is usually less data available in machine-readable formats than the application
contains
• Application Programming Interfaces (APIs) are based on variety of custom formats
and protocols, some of them non-standard (such as FQL and FBML in Facebook)
1 http://www.foaf-project.org/
2 http://www.sioc-project.org/
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Our observations fit well with statements by initiatives such as Open Social Web3,
Social Network Portability4, DataPortability5, OpenID6, OpenSocial7, born as a result
of a growing dissatisfaction in user communities.
2.1 Semantic Social Networks
Freebase claims to be an open database of the world’s information. It acquires
structured data spanning different domains such as music, people, and locations from
various sources such as Wikipedia and MusicBrainz8. The data is aggregated and
identical or related concepts are linked together. In addition, users in the community
can add, edit, and even upload data. Topics in Freebase are organized by types which
are grouped into domains. An important feature is that users not only can fill already
predefined types with instance data or edit it, but also create their own types and
define their properties, i.e. they can create new schemas and extend Freebase's
domain model using the same interface. However, it provides an open but proprietary
API for its data and encourages its use in applications and mashups.
DBpedia is a community effort to extract structured information from Wikipedia and
to make this information available on the Web. It provides an RDF dataset extracted
from Wikipedia, which contains mostly free text but also structured information such
as categories, lists, info boxes, links to external pages etc. DBPedia makes it possible
to ask complex queries (such as “German musicians who were born in Berlin”) over a
SPARQL query interface. DBPedia is a prime example of Linked Data publishing and
can be browsed using semantic browsers. It is interlinked with other semantic datasets
such as Geonames9, MusicBrainz etc.
3 Social network applications with semantic technologies
3.1 Creation of metadata
Folksonomies are the primary sources of metadata on Web 2.0, however they have
issues with consistency, ambiguity, synonymity. A next step beyond Web 2.0 is
Semantic Web. It has been observed how folksonomy tags evolve into property:value
triple-tags, which serve the same purpose as subject property object triple statements
in RDF. This phenomena has even been called “poor man's RDF” [13]. And thus
3 http://opensocialweb.org/
4 http://microformats.org/wiki/social-network-portability
5 http://www.dataportability.org/
6 http://openid.net/
7 http://code.google.com/apis/opensocial/
8 http://musicbrainz.org/
9 http://www.geonames.org/ontology/
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folksonomies move towards becoming lightweight ontologies. Social networks will
have to provide more sophisticated means to directly create RDF metadata, and
collaborative tagging will evolve into lightweight ontology development and integrate
into collaborative modeling of the social network domain.
3.2 User interface
Much work is left on the issue on how to present semantic data to the user in
applications, not to mention editing it [14]. There exists a number of semantic
browsers, such as Tabulator10, Disco11, OpenLink RDF Browser12, Objectviewer13,
Zitgist14. They are able to render generic RDF data for human users and navigate
through different data sources through RDF links, just as conventional Web browsers
navigate through HTML links. However, this kind of presentation most likely too
advanced for mainstream Web users (see Figure 1).
Figure 1 Tabulator view
We can assume that a Semantic Web application interface visualizes its domain
ontology so that each class and instance would have its own page, linked to others
through class-instance and instance-instance relationships. This approach, which we
call generic, is used in many semantic websites, and probably best illustrated by
Freebase. Another approach, which we call specific, is used by conventional Web
applications, as well as social networks. Every type of information (such as a car, a
user, or an event) has its own specific user interface. Each new type has to get a new
interface, the same interface cannot be used for different types, and interfaces have to
be fixed when the schema changes. This approach is obviously not feasible on the
10 http://www.w3.org/2005/ajar/tab
11 http://www4.wiwiss.fu-berlin.de/bizer/ng4j/disco/
12 http://demo.openlinksw.com/rdfbrowser/index.html
13 http://objectviewer.semwebcentral.org/
14 http://dataviewer.zitgist.com/
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Semantic Web, where ontologies are meant to be extended, reused, and integrated
from different sources. If social networks should become extensible semantic
applications, it is likely that they should adopt this generic approach.
3.3 Domain model
Social network applications (Last.fm, Flickr, LinkedIn etc.) are usually developed for
different application domains (music, photos, business). However, they share a
common property: the domains are fixed and non-extensible. Users are encouraged to
contribute and improve application data, but this is only limited to instance data for
predefined types. Semantic applications such as Freebase take a different approach
and allow users to edit the domain model itself: not only fill in instance data, but
extend and edit types, add new ones, and define properties in the underlying ontology.
Following this approach, social network applications would empower users to express
their identities by creating or reusing concepts and relationships relevant to them, and
share them with others. The domain model could be left to the community to control
and to develop it in a direction which is currently of most interest to it, keeping it
relevant over time. People would connect through things they have in common,
achieving object-centered sociality [10]. This may be achieved in the future by
integrating lightweight ontology development into the means of user collaboration
and content contribution. To implement this approach, applications need to be
modelled with semantic-enhanced languages such as: RDF/OWL, which offers more
expressivity than object-oriented and relational models, is based on formal semantics
and therefore interpreted unambiguously by different agents. Furthermore, they need
to reuse FOAF and SIOC ontologies, which currently are state of the art
representations of social networks on the Semantic Web, as well as other relevant
ontologies.
Most of the current SW applications are also static and fixed in the sense that
ontologies are known and mapped manually at design time [15]. Although semantic
technologies are designed with extensibility and openness in mind, current
programming languages and tools are not able to fully exploit it. It is expected that
future semantic applications will be using multiple ontologies, discover them and
integrate on request.
3.4 Publishing and reusing data and metadata
Large amounts of meaningfully interlinked RDF data available on the Web are crucial
for achieving the Semantic Web vision. However, many social networks do not offer
interfaces and APIs to access application data. Others make the contents of the
website (such as lists of users, songs, or pictures) available via simple read-only
REST interface in a software-processable data format, usually a custom schema of
XML, Atom, or RSS. Some provide full APIs with add/update methods, invoked via
various interfaces such as REST, XML-RPC, SOAP, Atom, or OpenSocial. A variety
of publishing formats (especially non-standard) make reuse difficult. We argue that
semantic social networks should publish their data in RDF, designed specifically for
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Workshop on Adaptation and Personalization for Web 2.0, UMAP'09, June 22-26, 2009
distributed knowledge representation. Furthermore, all resources in social networks
(including non-information, “real-world” resources) should be given URIs,
distinguished from URIs of representations that describe them, and published as
Linked Data15. APIs should be replaced by SPARQL endpoints, which would allow
running remote structured queries against application data. Semantic data
representation and advanced interfaces would help to overcome portability issues of
proprietary APIs and interconnect social networks with different data sources, enable
use of semantic browsers, and facilitate semantic mashups.
4 Prototype application design and implementation
The application prototype is a social network that allows users to browse events (such
as concerts and conferences) and places of interest (such as venues and hotels) and
find those that are most relevant to them. The prototype features a generic user
interface. Users are able to browse OWL ontology classes and their instances and see
properties with values, as represented in Figure 2.
Figure 2 Browsing the ontology in a Tabulator view
The application is able to import a list of friends from an external FOAF source. It
provides Linked Data access by serving interlinked RDF/XML which can be
15 http://linkeddata.org/
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visualized and browsed using semantic browsers such as Tabulator or reused in other
applications. It provides a SPARQL endpoint, which allows running structured
queries. It also implements a semantic mashup: when a page of an instance is
requested, the application queries remote DBPedia SPARQL endpoints, retrieves its
description and homepage address in real-time and presents it to the user in the same
fashion as local properties and values. Prototype is based on a RESTful Web
framework which treats HTTP resources as first-class objects and follows a Model
View Controller (MVC) pattern and W3C standards. Within the prototype the Model
is the ontology layer, the Java code is the Controller and Views are generated by
integrating SPARQL queries results and transforming them into XHTML using
XSLT.The application domain is modelled as a RDF/OWL ontology, stored in a RDF
triple store, accessed using Jena16, and queried using SPARQL.
Figure 3 Domain ontology graphical view
The domain ontology is based on FOAF and SIOC. It is implemented in OWL and
extends classes such as foaf:Person and adds a number of new classes such as: Place
and Event as represented in Figure 3. FOAF and SIOC classes and properties were
reused. Views become representations of REST resources (XHTML, RDF). They join
several SPARQL XML results and transform them directly to output XHTML using
XSLT, or serve raw RDF/XML for the Linked Data interface, depending on the
HTTP Accept header. Controller dispatches requests to resources which have explicit
16 http://jena.sourceforge.net/
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URIs, implement HTTP methods, can be related to domain instances using foaf:topic,
and return view representations.
Most of the current object-oriented languages are statically typed and do not allow
classes be changed or extended at run-time. I.e. it is not easy with the existing tools to
map Event class in OWL to an Event class in Java so that it could be changed or
extended at run-time. Tools such as RDFReactor17 and Elmo18 generate object-
oriented Java code from our ontologies, but this code is static and not extensible at
run time and therefore it was not used.
5 Conclusions and future work
Social data portability issues are leading to dissatisfaction in both user and developer
communities. They are caused by limited amounts of social data published openly and
lack of tools to import it, as well as formats and APIs of limited interoperability.
Social networks would benefit from Semantic Web technologies. FOAF, SIOC, and
Linked Data can solve portability issues and enable data reuse.
New generation of social applications could also take advantage of the advanced
means to model data that SW technologies provide. Semantic data representation and
advanced interfaces would help to overcome portability issues of proprietary APIs
and interconnect social networks with different data sources, enable use of semantic
browsers, and facilitate semantic mashups. Domain model could be collaboratively
developed by users of the application. This approach requires a new generic user
interface based on classes, instances, and properties. It could lead to more up-to-date
and relevant content, which would in turn facilitate social connections through points
of common interest. Other interesting directions that we have not yet pursued include
AJAX-enabled application interface, a form-based interface for SPARQL, and
dynamic, run-time object-ontology mapping tools.
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