Towards Semantically-Interlinked Online
John G. Breslin, Andreas Harth, Uldis Bojars, and Stefan Decker
Digital Enterprise Research Institute (DERI)
Abstract. Online community sites have replaced the traditional means
of keeping a community informed via libraries and publishing. At present,
online communities are islands that are not interlinked. We describe dif-
ferent types of online communities and tools that are currently used to
build and support such communities. Ontologies and Semantic Web tech-
nologies offer an upgrade path to providing more complex services. Fus-
ing information and inferring links between the various applications and
types of information provides relevant insights that make the available
information on the Internet more valuable. We present the SIOC ontol-
ogy which combines terms from vocabularies that already exist with new
terms needed to describe the relationships between concepts in the realm
of online community sites.
At the moment, most online communities are islands that are not linked. Sites are
hosted on stand-alone systems that cannot be interconnected due to application
and interface differences. Parallel discussions on interrelated topics may exist on
a number of sites, but their users are unaware of that. There is a huge amount
of related information that could be harnessed across such online communities,
from similar member profile details to common-topic discussion forums.
The goal of SIOC1(Semantically-Interlinked Online Communities) is to
interconnect these online communities. Community sites can include many dis-
cussion primitives, such as bulletin boards, weblogs and mailing lists, which we
have grouped under the concept of forum.
SIOC will facilitate the location of related and relevant information; by
searching on one forum, the ontology and interface will allow users to find infor-
mation on forums from other sites that use a SIOC-based system architecture.
Other uses include cross-site querying, topic-related searches, and the importing
of SIOC data into other systems, for example, using an email program to browse
data imported from a SIOC-enabled site. Therefore, SIOC tries to overcome the
serious limitations of current sites in making information accessible to their users
in an efficient manner .
A part of the task of linking on-line communities is to suggest additional
information related to any given forum and forum entry. One approach would
be to perform a search on, for example, post title, author, date, keywords or
the full post text in community sites. Existing Internet search engines locate
the information by performing a keyword search on a full-text index of Internet
resources. Some search engines try to improve the quality of search results by
analysing the link structure of web resources. But even with these improvements,
search engines lack an understanding of the information being searched for and
return a high number of irrelevant results. In this paper, we try to solve this
problem by narrowing the scope of a search to a set of interlinked community
sites and by describing the information in a machine-readable form using the
In a typical usage scenario, a user is searching for information on, for example,
installing broadband on a Linux-based PC in their house in Galway. There is
a post A discussing local ISPs on site 1, a bulletin board dedicated to Galway,
that references (on the HTML level) both a Usenet post B comparing broadband
modems and a mailing list post C detailing how to install broadband on Linux.
Previously the user would have had to traverse three sites to find the relevant
information. However, by making use of the SIOC ontology and remote RDF
querying, a search for broadband on the Galway bulletin board will also yield
the relevant text from the interlinked Usenet and mailing list posts B and C.
There are some challenges for SIOC. The grand challenge is adoption by
community sites, i.e. how can the users be enticed to make use of the SIOC
ontology. By using concepts that can be easily understood by site administrators,
and by providing properties that are automatically created by an end-user, the
SIOC ontology can be adopted in a useful way. A second challenge is how best
to use SIOC with existing ontologies. This can be partially solved by mappings
and interfaces to commonly-used ontologies such as Dublin Core2, FOAF3
and RSS 1.04. Another challenge is how SIOC will scale. If there are more
sites to query, then there are more potential relevant results, but also longer
response times and higher loads on the participating community sites. We will
keep the scaling challenge in mind when creating a future architecture for an
interconnected system of community sites.
The main contributions of this paper are the development of the SIOC ontol-
ogy and mappings to other RDF vocabularies, and a prototype to produce SIOC
metadata from a community weblog. These contributions will be detailed as fol-
lows. In section 2, we describe the SIOC ontology for linking information both
within and between community sites using RDF data, and demonstrate how
to map to other existing vocabularies (e.g., FOAF, RSS) and formats (email,
XHTML, etc.). In section 3, we will discuss the exchange of SIOC instances by
exporting and importing to web-based and legacy discussion systems as well as
RDF stores. Section 4 will describe some usages of the created instances, and
related work will be discussed in section 5. Section 6 concludes the paper.
In this section we present the SIOC ontology. The ontology consists of two major
parts: first, it contains classes and properties that describe discussion forums and
posts in online community sites. The ontology is available online5. Second, it
includes mappings that relate SIOC to existing vocabularies such as FOAF and
We have identifed the main concepts in online communities as Site, Forum,
Post, Event, Group and User. These are shown in Figure 1. While similar parent
concepts are found in other ontologies, it is the relationships, sub-classes and
properties of these concepts in the arena of online discussion methods that make
SIOC unique and provide use cases that were not previously possible.
2.1 Main Classes
We list the major classes that are used in the SIOC ontology, and describe their
usage in more detail.
Site is the location of an online community or set of communities, with users
in groups creating posts on a set of forums. While an individual forum or
group of forums are usually hosted on a centralised site, in the future the
concept of a “site” may be extended (for example, a topic thread could be
formed by posts in a distributed forum on a peer-to-peer environment).
Forum can be thought of as a channel or discussion area on which posts are
made. A forum can be linked to the site that hosts it. Forums will usually
discuss a certain topic or set of related topics, or they may contain discussions
entirely devoted to a certain community group or organisation. A forum will
have a moderator who can veto or edit posts before or after they appear in
the forum. Forums may have a set of subscribed users who are notified when
new posts are made. The hierarchy of forums can be defined in terms of
parents and children, allowing the creation of structures conforming to topic
categories as defined by the site administrator. Examples of forums include
mailing lists, online bulletin boards, Usenet newsgroups and weblogs.
Post is an article or message posted by a user to a forum. A series of posts may
be threaded if they share a common subject and are connected by parent
and child relationships. Posts will have content and may also have attached
files, which can be edited or deleted by the moderator of the forum that
contains the post.
Event is a virtual or real-world event with a single or multiple participants.
Examples include meet-ups associated with a particular user or set of users,
a meeting for subscribers of a certain community forum, or private task
reminders to a single user.
Fig.1. Overview of classes and properties used in SIOC.
Group is a set of members or users of a community site who have a common
role, purpose or interest. While a group of users may be a single community
that is linked to a certain forum, they may also be a set of users who perform
a certain role, for example, moderators or administrators.
User is a person who is a member of an online community. They are connected
to posts that they create or edit, to forums that they are subscribed to
or moderate, to sites that they administer, to other users that they know,
and to events that they organise or participate in. Users can be grouped for
purposes of allowing access to certain forums or enhanced community site
features (weblogs, webmail, etc.).
2.2 Important Properties
In the next paragraphs, we describe properties of SIOC concepts that are impor-
tant for extracting meaning from and for interlinking online community sites.
topic A topic definition applies to most of the concepts defined above, and topic
metadata can be a useful way to match documents and people to each other.
While it may be more difficult to require a user to assign a topic to a post
at creation time, it is more likely that a forum will have an associated topic
or set of topics that can be propagated to the posts it contains. Similarly,
users or groups can define topics of interest when their profiles are created
In order to enable the location of related information between the commu-
nity sites, a common categorisation system has to be used. On large scale,
general interest community sites, topics may be quite broad and a general
categorisation such as the DMOZ6category hierarchy may be used.
On specialised sites, which may have a very specific category hierarchy,
generic categorisation systems are not suitable because they are too broad
and may not have the necessary level of detail. For these sites, we propose
to define a category hierarchy in the SKOS framework  and to create
mappings between these concepts and a common category system. In future
work, SKOS may be used to describe all category schemes and mappings
between them, but the lack of generic taxonomies expressed in SKOS (since
it is in an early adoption phase) makes its current use difficult.
A proper use of topics can lead to many interesting scenarios in community
sites. For example, a user has defined certain topics of interest on registering
an account, after which forums matching those topics are suggested to the
views The views property represents the number of times a particular post or
user profile has been viewed. This is an example of where content is auto-
matically created by an end-user, and can increase the content’s importance
in terms of searching. For example, a user creates a query across a set of
SIOC-enabled sites, and is returned a list of subjects and extracts from cer-
tain posts, sorted by the popularity of the post, as indicated by the views
has sibling A recent development in online discussion methods is an article
or post that appears in multiple blogs, or has been copied from one forum
to another relevant forum. In SIOC, we can treat these copies of posts as
siblings of each other if we think of the posts as non-identical twins that share
most characteristics but differ in some manner. We can avoid duplication of
common data in the creation of siblings by linking to the new sibling, the
instance of which only contains the changed properties (in the example,
has container and topic would change). A sibling might also be a version of
a post in another language.
closed The closed property applies to posts in a threaded topic, but can also
be used for forums. It specifies the date and time that the post or forum was
closed. A closed property for posts is a useful for two reasons. Firstly, it is
used to specify that a particular post can have no more children. Secondly,
it gives us details of when the closure occurred, and can therefore be used
to determine how relevant in time a discussion or set of discussions may be.
has creator The has creator property links a post to the user profile of its au-
thor. Thus, we can follow the link from the post to the creator and locate
the other posts by the same person. The community can be seen as a net-
work of posts with users linked to each post, and there is also a network of
other posts created by a given user stemming from there. We can use the
information in community sites to locate more contributions by the given
knows The knows property is a basic property to show the structure of social
networks inside community sites. Who knows whom is the basic property
used for describing social network sites and provides information about the
links between community users. One of the options to locate relevant infor-
mation on a given topic is to search for information, not in the full scope of
the knowledge base, but in a subset of posts accessed by a person or friends
of that person. There are three possible types of knows links: linking to a user
inside the same community, to a user of other SIOC-enabled communities,
or to other resources outside SIOC.
One of the main functions of SIOC is to provide a means for exchanging commu-
nity instance data. Since there are already a considerable number of classes and
properties defined in RDF on the Web, we provide mappings in RDFS and OWL
to allow the import and export of SIOC instance data in different vocabularies.
Therefore, we can leverage the instance data that is already available.
We provide different kinds of mappings in RDFS for import and export us-
ing rdfs:subClassOf and rdfs:subPropertyOf, and also mappings in OWL using
owl:equivalentProperty and owl:equivalentClass together with other OWL con-
structs. The mappings to various other RDF vocabularies are online7. In Table
1, we show how classes in FOAF, RSS, and various email vocabularies correspond
to SIOC classes. Mappings of properties are described in a similar manner.
Carrying out the mappings requires a reasoning engine. Because of the various
open issues with regard to OWL reasoning, we split our mappings into two parts.
One part defines mappings in RDFS, which is somewhat limited in expressiveness
but there exist scalable reasoning engines that allow for reasoning of class and
property hierarchies and classification. A second part is encoded in OWL and
Table 1. Selected SIOC mappings
(from, to, cc) (author, name)–
describes more complex mapping constructs. At the current stage, we assume
that the mappings are carried out on community sites that export or import
data, but in theory the mappings can be completely decoupled.
Since mappings in SIOC are not only restricted to ontologies, we provide
means to extract information from simple data structures. For example, we might
want to map from XML documents into the SIOC ontology using XSL stylesheets
8. For that purpose, we provide an XSL stylesheet to extract data from XHTML
documents to create a SIOC Document instance. In the generic stylesheet, titles,
images, and hyperlinks are extracted from Web pages, somewhat similar to how
GRDDL9is used to extract information from XHTML documents.
Similarly, an XSL stylesheet can be used that maps from the XML-based
RSS formats (0.9x and 2.0) to RSS 1.0, and from there we have RDF mappings
to SIOC. Also, we have created a stylesheet that maps Atom10to SIOC, and
this is used for importing Atom files into SIOC. A mapping from SIOC to Atom
for data export requires a combination of queries against RDF data with an
Atom template where the appropriate values can be filled in.
3 Exchanging Instances
The core use of SIOC will be in the exchange of instance data between sites. In
the following, we elaborate on how the exchange, both importing and export-
ing data, can be carried out. We show how wrappers can help to achieve export
functionality, either based on exporting documents containing the information or
by rewriting queries. Another solution for incorporating the “document-based”
wrapping into a more sophisticated query infrastructure is to mirror the ex-
ported and converted RDF documents in an RDF data store and thus allow for
performing queries. We present a third solution, possibly for newly-developed ap-
plications, which uses a native RDF repository to store and retrieve statements,
making import and export straightforward.
3.1 Wrappers to Existing Tools
Wrappers will allow us to export instances of community site concepts such as
forums or posts in RDF format. They can also allow us to import SIOC instances
to other non-SIOC systems. While there are many possible kinds of community
sites for which wrappers could be developed, we will limit discussion to some of
them, divided into two categories - legacy systems that do not use HTTP as a
transport protocol, and web-based systems that can be accessed via HTTP.
Legacy Systems A large number of systems preceding the current Web are still
deployed and widely used on the Internet. Email is used for exchanging messages
and files in an asynchronous way, Internet Relay Chat (IRC) is widely used
for synchronous communication, and Usenet is still used to exchange messages.
Therefore, to really capture a large amount of data currently exchanged in online
communities on the Internet, these legacy systems and protocols need to be
considered for SIOC.
In contrast to web-based systems, where we just need to translate the data,
we need to employ protocol wrappers for legacy protocols to HTTP. For example,
for email we need to translate the data representation format from RFC82211
to SIOC, and provide a wrapper to the access protocol for email stores (usually
POP312or IMAP413). Wrappers can be either quite simple (just a dump of
the entire data set) or have some “intelligence” that allows for rewriting queries
posed over HTTP into the original data format and access protocol. If we also
provide importing facilities, for example into a mailing list, then we are building
a gateway between a SIOC site and the mailing list.
The email export wrapper accepts a conjunctive query over HTTP GET and
returns the results in SIOC. Parameters such as which posts to retrieve, the
time duration for results to be returned, etc. are encoded into the query. Certain
predicates can be used to restrict the set of posts to retrieve (such as modified at
> 2004-02-10). In a next step, the query is parsed and translated into IMAP4 to
send to the original data source. The original data source then returns the results
in RFC822 format, which is then translated back into RDF and returned to the
original caller via HTTP. We have implemented the wrapper and the mapping
using the Java programming language.
For imports, the email wrapper can receive sioc:Posts via HTTP PUT. Pa-
rameters needed for executing the mail sending process are also submitted via
a conjunctive query to have the same interface for both GET and PUT. The
posts are then translated into the RFC822 format that is suitable for sending
via SMTP. The wrapper can then return a status code indicating that the addi-
tion of data was completed correctly. The import part of the wrapper still has
to be implemented.
Interfacing with IRC requires a different approach than wrapping email since
the “data representation language” in IRC channel is just free-form text. In
IRC, so-called “bots” are responsible for the exchange of data. A very simple
bot just logs all utterings in an IRC channel and stores them persistently. More
complex bots can understand a defined syntax and perform actions based on
the commands issued. Also, some bots understand either a simple query syntax
or conjunctive queries that are posed inside the IRC channel. One bot we are
providing is logging the channel and recording URIs similar to the chump bot
14. The content that is accumulated is made available in RDF via query over
In addition to data that can be auto-generated from the existing sources, a
wrapper has to provide additional information which has to be manually added,
such as descriptions about mailing lists in sioc:Forum or general information in
Web-Based Systems Providing mappings from web-based systems is some-
what easier than mapping from legacy systems since protocol translation is not
We will discuss three kind of community sites using web-based systems - bul-
letin boards, weblogs and social networking sites. All these systems are based on
content management systems with different complexity levels. Therefore export-
ing and importing information from and to such systems can be accomplished
by adding wrapper interfaces to the existing content management systems.
For bulletin boards, some export functionality is already available (e.g. FOAF
from vB15and phpBB16, RSS from phpBB17). Most bulletin board systems use
a LAMP (Linux, Apache, MySQL, PHP/Perl) architecture, and a wrapper to
export data from these systems will use existing Perl and PHP libraries such as
XML FOAF, Magpie RSS, etc. However, most existing wrappers don’t export
their data in SIOC, and only provide a document-based export functionality
rather than a query interface.
Weblogs usually are small scale systems consisting of one or more contributors
and a community of readers. Most weblog engines already have RSS export
functionality and there are some experimental implementations of export of other
metadata, such as the Wordpress FOAF plugin18. Since the majority of these
engines are open source software, it is straightforward to modify existing export
functions to generate SIOC metadata. Import interfaces can be created in a
similar way, allowing weblogs to import SIOC data. One of the use cases for
SIOC import is replicating post entries among weblogs and community sites.
Social networking sites are based around the concept of persons and the rela-
tions between them. At the same time, many social networking sites are imple-
menting other functionality, such as bulletin boards or forums. There are existing
implementations of FOAF metadata exports of user profiles on ecademy.com and
Tribe.net. Similarly for bulletin boards, wrappers to export SIOC metadata on
posts and forums can be created using existing Perl and PHP libraries. How-
ever, many social networking sites are members-only and are not viewable to
the outside world, which raises a question of privacy and trust regarding the
information exported from these sites. The issue of privacy can be partially ad-
dressed by exchanging sensitive information only among a closed network of
trusted community sites.
Fig.2. SIOC metadata export from WordPress
The main challenge for using SIOC with web-based systems are not in the
technical implementation of SIOC wrappers, but rather in the wide adoption of
the SIOC ontology to gain incentives for people to provide data and tools for
By making SIOC data available through exports, we are encouraging the
adoption of SIOC concepts. To this end, we have created a SIOC metadata export
facility19for the WordPress weblog engine. This makes use of existing WordPress
PHP functions to access the information about posts, users and forums (weblog
channels) from the underlying relational database. SIOC metadata in RDF is
generated for each concept instance. The export process is illustrated by example
in Figure 2. Other export facilities are being written for the bulletin board
systems phpBB and vBulletin, and the content management system Drupal.
3.2 Mirror Data in RDF Store
Most of the web-based wrappers just provide simple document-based export
facilities. Replacing the simple wrappers with full-featured wrappers that are
capable of query rewriting takes time. Since our goal is to make SIOC data
available for query and to entice people to use SIOC now, we need a method to
allow querying of the information that sites publish in flat files.
A solution to provide query facilities for sites that have only simple data
export facilities is to replicate the information in a data store that can process
queries. Queries are then answered from the replica. The replica is updated
either by a scutter - an RDF crawler that traverses rdfs:seeAlso links - that
periodically crawls the data, or by the original site that pushes updates and
changes automatically into the mirror store once the data changes. If the data
is exported in a format other than SIOC, then the system also needs to include
a component that carries out the mappings from the vocabulary that is used to
export data into SIOC.
Replicating the contents of the entire site from the relational database to
an RDF store may work initially and create an easy upgrade path. However, in
the longer term, storing and integrating data in a native RDF repository is the
3.3Native RDF Store
The previous two subsections discussed tasks that concerned querying existing
sites and their content. We will now describe how newly architectured sites can
make use of a native RDF repository to store their data.
Exporting data is quite simple because RDF does not restrict you in the
way data can be expressed. On the flip side, the flexibility of RDF creates a
problem when importing data into systems with a fixed schema. Issues arise
here, for example, when an application is importing data using a given schema,
and certain mandatory data is missing.
Since community sites provide access to complex structures of information
with different types, it is natural to store that information in RDF directly.
Repositories such as Jena2 , Sesame , Redland , or YARS  can be
used to store and retrieve the data. With an RDF store as the data repository,
importing and exporting information is straightforward, and also data integra-
tion tasks can be facilitated. An API similar to the RDF NetAPI  can be
used as well. The route we chose for SIOC is to use a restful interface that uses
HTTP methods such as PUT and DELETE for adding and removing data.
We can use an RDF repository as the data store and build the application
functionality on top of the repository in a way that is flexible in regards to the
schema. The user interface should also function when pieces of data are missing,
since we cannot control which data (added or removed from the underlying RDF
store) is agnostic to any schema definition.
4 Using SIOC Data
Given the ontology, the mappings, and the wrappers, we are now able to pose
queries and add data to individual SIOC sites.
Once we have made the data available using a common query infrastructure, we
can use various user interfaces to navigate SIOC data. The simplest solution is to
use a mapping from SIOC to a data format where client programs already exist.
For example, SIOC data can be mapped to email and then read in any email
program. Also, a mapping from SIOC to RSS allows us to navigate a subset of
SIOC information inside a regular RSS news reader. Since SIOC has a richer
data model than RSS, some information will be lost during the conversion.
Another approach is to use existing RDF browsers such as BrownSauce20
to view arbitrary RDF data. Leveraging the full potential of SIOC requires
the provision of custom programs and user interfaces specially tailored towards
However, since most programs are already providing browsing facilities for
their underlying data structures, implementing import facilities for those pro-
grams allows the seamless integration of data without the need for new user
Representing data in SIOC enables users to pose structural queries against the
collected data rather than just having keyword search. An implication of struc-
tural queries is that you get precise answers as a result, and not just pieces of
documents that match the keyword.
Until now, we have only considered querying one community site in isolation.
However, since sites are linked together, we might want to perform queries across
similar community sites that all share some connections.
One central problem in P2P networks is how to route queries . We plan
to exploit the link structure that connects forums or sites to route queries. The
forum and site linkage inside SIOC makes it easier to do routing than in general-
purpose peer-to-peer networks, since we have some (human-created) links that
can be exploited. We expect a scale-free behaviour of these links once SIOC is
widely used in practice.
By building the infrastructure for distributing queries into the different site
management software or wrappers, we can perform queries without any central
components. As a result, querying inside an intranet will be simple and already
integrated into the tools used to manage the different community sites inside an
organisation, such as mailing lists or forums.
4.3 Locating Related Information
Querying the community sites for information on demand is not the only model
of end-user interaction. Another way to enhance the end-user experience is to
prepare the data in advance, at creation time of a post.
Once a new post is created in a community site and the SIOC information
is available, this site then queries the network of community sites to find related
posts. A query is performed based on the post metadata, such as other posts by
this person or other posts in the set of the post’s topics.
After the information about related resources is received, the community
site stores this information using a related to property. Information about the
resources the article links to is also extracted from the post body and stored in
a links to property. These properties can then be reused by other users of SIOC
data and by SIOC and RDF browsers to browse forum entries and navigate
through the web of interlinked posts, independent of the underlying site structure
that the forums and posts are hosted on.
The results of this information retrieval model are the enhanced function-
ality added to community sites, and better scalability since the information is
prepared in advance.
5 Related Work
Harvest is an early system  that can be used to gather information from diverse
repositories to build, search, and replicate indexes, and to cache objects as they
are retrieved across the Internet. Harvest uses the Summary Object Interchange
Format (SOIF) to exchange metadata about resources. In contrast, SIOC uses
RDF as the exchange format and allows for mappings between different vocab-
ularies, which is not envisioned in SOIF. The various Harvest subsystems are
arranged in a hierarchical fashion, similar to the Domain Name System. We do
not have any specified way of accessing resources in SIOC, but intend to apply
database techniques for query processing and integration.
Various approaches for data integration on the Web, such as data repre-
sentation languages, structural information retrieval, and query processing, are
surveyed in . The survey also describes the warehousing approach to data in-
tegration that aggregates all information at one central site. However, advanced
database techniques have failed so far to surface on the Web. SIOC is a first step
in providing a common vocabulary for data representation across online com-
munities. In further work, we plan to apply usable techniques from the database
community to web data integration problems.
At the moment, RDF Site Summary (RSS 1.0) is widely used in weblog
systems and news sites. RSS 1.0 defines a lightweight vocabulary for syndicating
news items, but is used for all sorts of data exchange. Although RSS works
well in practice, there are several issues: firstly, only the last “n” news items are
typically exported in RSS. There is no standardised way of accessing older posts.
Secondly, there is an issue with regard to updates. Different vocabularies have
different update semantics: where RSS usually provides a stream of news items
that should be accumulated over time, changes in FOAF files mean that the
previous version should be replaced by the current. Because vocabularies can be
mixed in the same file, determining what update semantics to apply for a certain
file is difficult. Thirdly, although there exists a large number of extensions, none
of the advanced functionality of RSS is widely deployed, since tools lack support
for creating and using the extensions. RSS is widely adopted in certain areas,
such as weblogs, but is not used in a wider context such as bulletin boards,
mailing lists, Usenet, wikis, etc.
Also, TrackBack21is a system implemented by many blogging tools that
allows a weblog article to be linked to the followup articles. This is achieved by
sending a summary and metadata of the new article to the weblog containing
the original article, and adding this information to the original article. Link-
ing together cross-site conversations is a step in the direction of semantically-
interlinked online communities; however there are limitations to TrackBack.
Firstly, it is being used in a very limited number of weblog entries and in most
implementations the author has to manually enter the TrackBack address. Sec-
ondly, it only connects two individual instances of posts, not reflecting the links
to the community and, in the case of archived post entries, the readers may
even be unaware of the existence of this new link. Thirdly, TrackBack does not
have a machine readable representation that would allow one to export its link
semantics in RDF, to aggregate the resulting information and reuse it to identify
related post entries.
We have presented the SIOC ontology and various mappings to and from other
vocabularies that are already deployed on the Web. We have described how
instance data in SIOC can be exchanged among online community sites. Our
initial SIOC ontology can also be used to enable more complex use cases, for
example cross-site structural queries, and integration based on the warehousing
To tackle the challenge of adoption, we have provided an upgrade path that
allows a gradual migration from existing systems to semantically-enabled sites.
For combination with other ontologies, we have presented mappings to and from Download full-text
SIOC that allow the export and import of SIOC data using existing systems
and tools. We have developed a prototype SIOC exporter for a weblog engine,
and several more are in development. In the future, we intend to exploit the
characteristics of intra- and inter-site links to guide query routing in a P2P-like
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