=Paper=
{{Paper
|id=None
|storemode=property
|title=Linked Services and the Future Internet
|pdfUrl=https://ceur-ws.org/Vol-700/Paper11.pdf
|volume=Vol-700
|dblpUrl=https://dblp.org/rec/conf/fia/PedrinaciD10
}}
==Linked Services and the Future Internet==
https://ceur-ws.org/Vol-700/Paper11.pdf
Linked Services and the Future Internet
Carlos Pedrinaci1 and John Domingue1
Knowledge Media Institute, The Open University
Walton Hall, Milton Keynes, MK7 6AA, UK
(c.pedrinaci, j.b.domingue)@open.ac.uk
Abstract. It has often been argued that Web services would have a
tremendous impact on the Internet, as a core enabling technology sup-
porting a highly efficient service-based economy at a global scale. How-
ever, despite the outstanding progress in the area we are still to witness
this impact. In this paper, we analyse the state of the art highlight-
ing the main reasons we believe have hampered their uptake. Based on
this analysis, we further discuss about current trends and development
within other fields and argue that the recent evolution, notably Linked
Data and Web 2.0 technologies, provides the missing ingredients that
will lead to a new wave of services – Linked Services – that will drive
the creation of complex systems in the Future Internet. Throughout the
presentation of this vision we outline the main principles underpinning
Linked Services and we illustrate how they can be implemented using
a number of technologies and tools we have developed and are in the
process of extending.
1 Introduction
The Internet has driven to a large extent the evolution of Information and Com-
munication Technologies in the last years as well as it has been at the core of a
number of outstanding socio-economic changes across the globe. Not surprisingly
major efforts are devoted to both analysing and extending or improving it. The
Future Internet initiative is one such effort focussing on both anticipating and
devising the technologies for the forthcoming years. These efforts span from the
lowest layers such as hardware and software for improving network communica-
tions to the highest layers enabling the creation of a service-based economy over
the Internet.
In this position paper we shall focus on the service layer from a technical
perspective. We shall highlight the existing limitations of current technologies
in the area and we shall propose a set of simple principles and technologies that
overcome these drawbacks. The approach described herein is centred on the
integration of service technologies and Linked Data as means to both augment
the potential and applicability of Linked Data and to remedy existing limitations
of Web services enabling their use on a Web scale.
Throughout this paper we argue that essential to the evolution of the Internet
towards enabling the creation of highly advanced applications and businesses is
the systematic description of reusable software services and related information
as Linked Data better enabling their discovery and interpretation. Similarly, we
also argue that the emerging Web of Data is currently in need for means and
technologies supporting the systematic, maintainable, and efficient development
of (complex) applications, and services represent the right abstraction for this.
We anticipate that this integration will mitigate the existing limitations of both
services and the Web of Data, giving birth to a new wave of highly advanced
applications for the Future Internet.
2 The Current State of Affairs
Web Services and the Service-Oriented Architecture are commonly lauded as
a silver bullet for Enterprise Application Integration, implementation of inter-
organizational business processes, and even as a general solution for the de-
velopment of all complex distributed applications. Despite the appealing char-
acteristics of service-orientation principles and technologies, their uptake on a
Web-scale has been significantly less prominent than initially anticipated [5].
First and foremost Web services, despite their name, are hardly a Web-oriented
technology [17] but rather one suited for enterprises which so far have been reluc-
tant to publish functionality on the Web. Secondly, from a technical perspective,
current technologies are such that software developers need to devote a signifi-
cant effort to discovering sets of suitable services, interpreting them, developing
software that overcomes their inherent data and process mismatches, and finally
combining them into a complex composite process.
Semantic Web Services (SWS) [10] have tried to overcome Web services lim-
itations by enriching them with semantic annotations in order to better support
their discovery, composition, and execution. Up until now, however, the impact
of SWS on the Web has been minimal. In fact, although SWS technologies have
already shown their benefits, e.g., in discovery [15], research in the area has
failed to take into account the socio-economic aspects devoted to the creation
and annotation of services. First, research has mostly focused on devising highly
expressive conceptual models glossing over the complexity they introduce and
the additional effort demanded of users. Second, SWS research has for the most
part targeted WSDL/SOAP based Web services which are not prevalent on the
Web [5]. As a consequence, SWS is instead a niche technology only accessible to
highly trained experts and the benefits obtained are most often not considered
worth the additional investment.
In parallel, the Web is currently witnessing a dramatic change with the advent
of Web 2.0 [7]. Web 2.0 technologies are “socialising” the Web, putting individ-
uals at the core of the Web as both data producers and consumers. Web 2.0
technologies have shown that collaboration over the Web can produce outstand-
ing results with a low cost, and it is also encouraging enterprises and institutions
to offer their data and services publicly at a previously unprecedented scale and
pace [7, 5]. Unfortunately, Web APIs are generally described using plain, un-
structured HTML. As a consequence, and despite their popularity, discovering
Web APIs or developing mashups that integrate disparate services in this man-
ner suffers from a number of limitations similar to those affecting “classical” Web
services, with an increased complexity since most often no machine-processable
description is available.
Finally, Linked Data technologies [2] have given birth to the Web of Data,
“a Web of things in the world, described by data on the Web” [2]. The Web of
Data, impelled by the current trend towards an open Web, has recently exper-
imented an outstanding growth and currently provides publicly large amounts
of interconnected data concerning a wide range of domains [2]. The outstand-
ing growth of the Web of Data is urging researchers to devise means to exploit
the valuable information it exposes. Among the main applications produced so
far there are a number of data browsers that help people navigate through the
data. There are systems that crawl, index and provide intelligent search support
over the Web of data like Sindice [11] and Watson [4]. And finally, there are a
few domain-specific applications such as Revyu.com [6]. Although useful these
applications hardly go beyond presenting together data gathered from different
sources leaving the potential of this massive data space unexploited. It is there-
fore becoming of crucial importance to devise ways in which smart applications
that exploit the Web of Data could be systematically developed.
3 Services and the Web of Data: An Unexploited
Symbiosis
We believe that services and the Web of Data are characterised by a number
of complementary features that can mitigate each other’s limitations and can
ultimately enable the development of highly advanced applications and services
as envisioned for the Future Internet [12]. In the remainder of this paper we shall
refer to this new kind of services as Linked Services.
On the one hand, from a technological perspective, the evolution of the Web
of Data is highlighting the fact that light weight semantics yield significant ben-
efits that justify the investment in annotating data and deploying the necessary
machinery. This initiative is contributing to generate an outstanding body of
knowledge that can help to significantly reduce the effort for creating semantic
annotations for services. Furthermore, it also represents a significant use case
for the application of services technologies on a Web scale in order to process
this wealth of data which remains nowadays largely unexploited. On the other
hand, from a socio-economic perspective, the recent evolution around Web 2.0
has shown that collaboration over the Web can lead to large quantities of very
useful data with a low cost. Similarly, both Web 2.0 and more recently Linked
Data technologies are encouraging enterprises and institutions to offer their data
and services publicly enabling open innovation on a Web scale. This new scenario
provides in our view suitable technologies and data, as well as the necessary eco-
nomic and social interest for the wide application of services technologies on a
Web scale.
Fig. 1. Linked Services for the Web of Data.
The vision toward the next wave of services – Linked Services – previously
presented in [12] and depicted in Figure 1, is based on two simple ideas: publish-
ing service annotations in the Web of Data, and creating services for the Web of
Data, i.e., services that process Linked Data and generate Linked Data. In a nut-
shell, Linked Services are services described as Linked Data. Therefore, these are
service descriptions whereby their inputs and outputs, their functionality, and
their non-functional properties are described in terms of (reused) light weight
RDFS vocabularies and exposed following Linked Data principles. In fact, as
such, Linked Services descriptions represent highly valuable information which
is still to be provided in the Web of Data: data about reusable functionality on
the Web. Secondly, by virtue of these descriptions, Linked Services are therefore
services that, with appropriate infrastructure support, can consume RDF from
the Web of Data, and, if necessary, can also generate additional RDF to be fed
back to the Web of Data. In other words, Linked Services constitute a processing
layer on top of the wealth of information currently available in the Web of Data
which remains unexploited.
4 Services on the Web of Data
Before any significant uptake of services can take place on the Web, proper
mechanisms for creating, publishing and discovering services must be in place.
In this respect the state of the art shows that:
– Semantics are essential to reach a sufficient level of automation during the
life-cycle of services and applications,
– finding an adequate trade-off between the expressivity of the service model
used and the scalability from a computational and knowledge acquisition
perspective is key for a wide adoption of service technologies,
– the annotation of services should be simplified as much as possible, and
“crowdsourcing” appears to be a particularly effective and cheap solution to
this end,
– on the Web, light weight ontologies together with the possibility to provide
custom extensions prevail against more complex models,
– any solution to deploying services that aspires to be widely adopted should
build upon the various approaches and standards used on the Web, including
Web APIs, RDF, and SPARQL,
– Linked Data principles [2] represent nowadays the best practice for publish-
ing data on the Web both for human and machine consumption,
– links between publicly available datasets are essential for the scalability and
the value of the data exposed.
The principles we have just highlighted have an impact in a wide range of
activities during the life-cycle of services, notably during the annotation, publi-
cation, discovery, and use of Web services and Web APIs on the Web. We shall
cover these in the remainder of this paper.
4.1 Semantic Description of WSDL Services and Web APIs
The semantics of a service, or software component, are typically divided into four
kinds: i) data model; ii) functional semantics; iii) non-functional semantics; iv)
behavioural semantics. The level of refinement with which software components
can be manipulated (e.g., discovered, composed, invoked), depends directly on
the level of detail with which their semantics are captured and exposed.
In our current work we build upon the Minimal Service Model (MSM) [8, 13],
WSMO-Lite [18] and hRESTS/MicroWSMO [8], for capturing the semantics of
services as Linked Data. In a nutshell, the MSM is a simple RDF(S) integration
vocabulary which captures the maximum common denominator between existing
conceptual models for services. Thus, the MSM is an integration model at the
intersection of existing formalisms, able to capture the core semantics of both
Web services and Web APIs in a common model, homogeneously supporting
publication and discovery.
The MSM is enriched with WSMO-Lite and hRESTS/MicroWSMO. The
former provides a very simple RDFS ontology together with a methodology for
expressing functional and nonfunctional semantics, and an information model for
WSDL services. The latter is a microformat-like1 notation that forms the basis
for our work on semantically describing Web APIs. It enables the creation of
machine-processable Web API descriptions based on available HTML documen-
tation by allowing one to structure APIs descriptions and by including pointers
to the semantics of the service, operations, and data manipulated.
4.2 Supporting Services Annotation
Arguably, one of the main limitations of previous approaches to integrating ser-
vices in the Semantic Web, has been the difficulty from an annotation perspec-
tive. The use of light weight ontologies as opposed to highly expressive conceptual
models reduces considerably the effort involved and the amount of annotations
to be provided. Additionally, and more importantly, the Web of Data is signifi-
cantly changing the environment from an annotation and usage point of view.
On the one hand, the Web of Data can be used as background knowledge [4]
in order to provide suitable ontologies that can be used, extended, and com-
bined to create domain ontologies for annotating services in an easier manner.
On the other hand, generating service annotations by reusing existing ontologies
directly contributes to increasing services usability and presumably their uptake.
For instance annotating services inputs and outputs with respect to existing vo-
cabularies ensures the direct applicability of services over data already available
as well as it allows Linked Data application developers to carry out data driven
discovery of services by simply checking the input and output types of services.
From a more abstract perspective, this process ensures that services modeled in
this way are linked to the Web of Data as encouraged by Linked Data principles.
We are currently devoting significant efforts to creating tools that support
users in the annotation of services based on the principles introduced above. One
such application is SWEET [9] which is, to the best of our knowledge, the first
tool that enables the creation of semantic annotations for Web APIs and REST-
ful services. SWEET provides user support for creating hRESTS/MicroWSMO
annotations over any HTML page describing Web APIs, therefore supporting a
non-intrusive incremental annotation of existing resources. The tool, assisted by
Watson [4], supports users in browsing the Semantic Web while annotating ser-
vices so that they can identify suitable vocabularies such as FOAF [3], and use
them for the annotation. A tool called SOWER, based on the same principles
but focussing on the annotation of WSDL services, has also been developed.
4.3 Publication and Discovery of Services on the Web of Data
At present, service descriptions can only be retrieved through the Web of doc-
uments, which is essentially designed for human beings, or through specific in-
terfaces to registries such as UDDI that have failed to gain significant uptake.
A fundamental step for bringing services closer to the Web is their publication
1
See http://www.microformats.org
based on current best practices. We view service annotations as a particular
kind of highly valuable data: data that informs us about existing reusable func-
tionality exposed somewhere on the Web that processes and/or generates data.
As such, services should therefore be published on the Web according to current
best practices for publishing data – Linked Data principles – so that applications
can easily discover and process their descriptions on the basis of the very same
technologies they use for retrieving data.
In order to explore and validate these principles we have developed iServe [13],
a public platform that unifies service publication and discovery on the Web
through the use of Linked Data. iServe builds upon lessons learnt from research
and development on the Web and on service discovery algorithms to provide a
generic semantic service registry able to support advanced discovery over dif-
ferent kinds of services described using heterogeneous formalisms. iServe uses
as its core conceptual model the MSM and it currently includes a number of
import mechanisms able to deal with a large variety of Web service and Web
APIs description formats.
Once imported, iServe publishes the semantic annotations of services as
Linked Data and provides a number of semantic discovery methods including
SPARQL, or more refined algorithms exploiting the semantic descriptions of
services, RDFS inferencing, and similarity measures for more accurate results.
The current implementation already shows how Web services and Web APIs
can be described by means of an homogeneous conceptual model – the Minimal
Service Model – and how they can be published as Linked Data, therefore better
promoting their discovery based on the use of the well established and adopted
Linked Data principles.
5 Services for the Web of Data
The notion of services as well-defined, independent, invokable and distributed
pieces of functionality is indeed a very powerful architectural notion for devel-
oping distributed systems. Encapsulating functionality in this way provides the
capacity for maintaining a loose coupling between integrated components which,
when it comes to an environment like the Web, appears as a highly beneficial
(if not necessary) feature. Services provide therefore a suitable architectural ab-
straction for the integration of processing capabilities over the Web of Data in
a loosely coupled manner.
5.1 Integrating Legacy Systems
Currently a good part of the Web of Data is generated from existing databases
by using tools such as D2R [2]. There is, however, a large body of informa-
tion exposed through Web APIs by companies which are either not interested
in offering all the information publicly on the Web given its commercial value
and/or its sensitivity, or because they do not have the technical skills or interest
in exposing the information as Linked Data. Similarly, in the Internet of Things,
there is a growing number of streams of data provided by sensors through highly
heterogeneous formats and interfaces, which exhibits considerable integration
and processing limitations [16].
We previously highlighted that Linked Services are such that their inputs
and outputs are RDF. As a consequence, they represent a natural means for
exposing as Linked Data valuable information previously enclosed within silos,
through the annotation of existing Web APIs and WSDL services. Web APIs
could in this way be invoked by interpreting their semantic annotations, and
RDF information could be obtained on demand. In this way, data from legacy
systems, state of the art Web 2.0 sites, or sensors, which do not embrace Linked
Data principles could be made available as Linked Data easily.
This approach is currently being explored in the context of a number of use
cases from the European project SOA4All [5]. Our current experience, although
preliminary at this stage, shows already the applicability and potential of bring-
ing legacy systems to the Web of Data in this manner.
5.2 Processing Linked Data
Integration and fusion of disparate data coming from the Web of Data hardly
takes place nowadays and therefore applications do not perform any ulterior
processing of this data other than for presenting it to the user [2]. Generating new
data based on what has been found or the provisioning of added-value services
that exploit this data thus remains a pending issue. For instance, something as
simple and useful as a unit transformation service is still to be provided for the
Web of Data. There is a clear need for enabling the processing of Linked Data in
ways such that application developers could conveniently apply them over data
gathered at runtime to carry out computations as simple as unit transformations,
more complex as deriving similarities between products or services based on the
reviews published by users, or even more advanced like booking a trip.
It seems natural to approach the development of systems that process Linked
Data by composing Linked Services. These services should be able to consume
RDF data, carry out the concrete activity they are responsible for, and return
the result, if any, in RDF as well. The invoking system could then store the
result obtained or continue with the activity it is carrying out using these newly
obtained RDF triples combined with additional sources of data. In a sense this
is quite similar to the notion of service mashups [1] and RDF mashups [14] with
the important difference that it supports generic services which are, in this case,
RDF-aware and their functionality may range from RDF-specific manipulation
functionality up to highly complex processing beyond data fusion.
It is worth noting in this respect the benefit brought by having service de-
scriptions in the Web of Data. When developing applications that process Linked
Data, discovering useful services could be driven by the data that needs to be
manipulated. The reuse of ontologies and vocabularies would in turn contribute
towards increasing the compatibility of services. In this way, Linked Data appli-
cation developers would have access to an ever growing body of reusable com-
ponents ready to be combined and exploited. Integrating services with the Web
of Data as depicted before would give birth to a services ecosystem on top of
Linked Data, whereby people would be able to collaboratively and incrementally
construct complex systems by reusing the results of others, gradually supporting
the development of increasingly complex applications for the Future Internet.
6 Conclusions and Outlook
Despite the appealing characteristics of service-orientation principles and tech-
nologies, their uptake on a Web-scale has been significantly less prominent than
initially anticipated. The Web is witnessing a dramatic evolution with the advent
of Web 2.0 and Linked Data technologies. Web 2.0 has triggered a socialisation
of the Web which has placed individuals at the centre of the Web and is widely
based on somewhat altruistic contributions of free data and manual labour from
users. The Linked Data initiative is in turn devoted to creating what is referred
to as the Web of Data, which already provides publicly large amounts of inter-
connected data concerning a wide range of domains described in terms of light
weight ontologies for supporting automated processing.
We have explored the relationship between services and the Web of Data. In
particular we have highlighted that Linked Data represent appropriate principles
for publishing services on the Web. We have illustrated how Web services and
RESTful services can be brought into the Web of Data by means of simple
RDF vocabularies and supporting tools. We have highlighted the fact that the
current evolution of the Web of Data is gathering the necessary motivation
for the development of advanced applications that process Linked Data. We
have outlined that Linked Services are particularly well-suited for supporting
developers in creating applications that process Linked Data.
The overall vision outlined herein represents the roadmap for the research
we are currently carrying out trying to expand the capabilities of the Linked
Data applications as well as trying to promote and support the use of services
on the Web through light weight semantic annotations. This research, like the
principles it builds upon, will strive to provide data, resources, tools and engines
publicly on the Web in order to eventually lead to the wider uptake of services
on a Web scale.
7 Acknowledgements
This work is partly funded by the EU SOA4All project. We would like to thank
all the members of the SOA4All project for their contribution.
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