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Our method fosters ideas from both approaches:
it defines the core objects of the SocIoS API domain
through an ontology which helps to modeling these
objects to the underlying SNS APIs using software
wrappers (formally called SocIoS adaptors). To
build this ontology we start with the conceptual
analysis of the application scenario in order to
capture the main domain concepts. These include the
notions of User, Activity, Group, Multimedia item,
Event, Location and Message. Next, we study a
number of SNSs in order to identify the API objects
that are semantically equivalent to the domain
concepts. This helps us to place the domain concepts
in the SNS context and examine their relationships
and position in the object model hierarchy. The
combination of these approaches leads to a
conceptualization of the SocIoS domain that is
formally captured in the presented SocIoS ontology.
The objective of this ontology is to provide the
necessary flexibility of the SocIoS object model so
as to be extended as necessary when new SNS APIs
or application domains are to be included later in its
lifetime. The model is captured using the ontology
specification language (OWL) (McGuinness, 2004)
that only includes the information that is necessary
for an object model. We directly derive the initial
SocIoS object model from this ontology. When in
the future the SocIoS object model needs to be
expanded, the ontology will have to be expanded
first, adding the logical relationships between classes
that provide a real ontological definition. This
ensures that the new definitions are logically correct,
i.e. satisfy the conceptualization of the SocIoS
ontology. Then, a new SocIoS object model is
derived by simplifying from the new ontology.
The document is structured as such: Section 2
provides the related work in specifications and APIs
that have similar goals as ours as well as ontologies
from which our approach can adopt concepts so as to
be extendible. Section 3 presents the domain
concepts of SocIoS as the conclusion of an analysis
of three real-world application scenarios. In Section
4 the derived domain concepts are projected to
existing objects of a group of an appropriate
selection of SNS APIs. Finally, Section 5 gives the
SocIoS ontology as a result of this analysis and
discusses the lower level parameters of the concepts.
2 RELATED WORK
There have been a number of approaches to build a
meta-API so as to implement functionality
federation and data marshaling from numerous
SNSs. However, as stated above, the majority
comprise proprietary solutions which limits the
extensibility of the platforms to non-supported APIs.
Such examples are GNIP®, hootsuite® and
Stroodle®.
Even though we study a number of SNS APIs so
as to identify the dominant objects that they
commonly use, our solution uses mainly OpenSocial
(OpenSocial, 2010) as a reference specification.
OpenSocial defines a common API for social
applications across multiple websites. As it is a
product of collaboration of a broad set of members
of the web community it naturally encompasses the
most dominant SNS concepts. However, OpenSocial
is not meant to be used as a meta-API or an
aggregator. This results in two reasons for which
OpenSocial cannot meet our requirements: a) it is
not meant to be adaptive, but rather requires from
the underlying APIs to adapt it, and; b) it is
overdetailed, providing an extreme number of
second-class objects that cannot be mapped to
existing API concepts. The issue of adaptability, is
the one that mainly led us into seeking an ontology
solution.
By defining the SocIoS universe of discourse,
we assume that we will manage to capture the
common denominator of the core SNS applications.
This universe can be used at a higher layer by any
service. However, here, we need to make a clear
separation. With this work we do not want to model
the real world concepts that appear in the SNS as a
result of their use. E.g. we are not interested in
concepts that derive from tagging multimedia
content since this involves practically everything.
Various efforts have been put on that aspect with the
most prominent work being the one of (Mika, 2007).
It is obvious that in the frame of an SNS a user can
essentially import and define anything using any
type of description, essentially capturing the whole
world (or a new world for what is worth). Various
crowdsourcing techniques have been proposed for
that purpose and most of the SNS encompass
functionality for meeting this particular objective
(e.g. tagging mechanisms).
Instead we are focusing on conceptual entities
that are manifested in the object models of the
existing SNSs. By using agreed-upon Semantic Web
formats to describe people, content objects, and the
connections that bind them together, SNSs can
interoperate by appealing to common semantics
(Breslin, 2007).
To this end we analyze the existing work in the
area of formal specifications of the SNS domain so
as to investigate if and how there are ontologies that
already capture notions that our approach would like
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