Rights expression languages declare the permitted and prohibited actions to be performed on a resource. Along this work, six rights expression languages are compared, abstracting their commonalities and outlining their underlying pattern. Linked Data, which can be object of protection by the intellectual property laws or its access be restricted by an access control system, can be the asset in rights expressions. The requirements for a pattern for licensing Linked Data resources are listed

Gómez-Pérez, A.

Poveda-Villalón, María

Rodríguez Doncel, Víctor

Suárez-Figueroa, Mari Carmen

Archivo Digital UPM

Licensing patterns for Linked Data

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

Licensing Patterns for Linked Data ⋆
Vı´ctor Rodr´ıguez-Doncel, Mari Carmen Sua´rez-Figueroa, Asuncio´n
Go´mez-Pe´rez, and Mar´ıa Poveda-Villalo´n
Ontology Engineering Group, Universidad Polite´cnica de Madrid, Spain
{vrodriguez,mcsuarez,asun,mpoveda}@fi.upm.es
Abstract. Rights expression languages declare the permitted and pro-
hibited actions to be performed on a resource. Along this work, six rights
expression languages are compared, abstracting their commonalities and
outlining their underlying pattern. Linked Data, which can be object of
protection by the intellectual property laws or its access be restricted
by an access control system, can be the asset in rights expressions. The
requirements for a pattern for licensing Linked Data resources are listed.
Keywords: licensing, Ontology Design Pattern, linked data
1 Introduction
The Linked Data initiative describes how to publish data into a single global
data space in the Web [1]. Yet, the mere publication does not entitle the web
visitors to use the data for any arbitrary purpose, as data may be protected
by intellectual property laws or database laws [2]. In order to use the data, a
general license or a private contract must exist, and their terms be respected.
Rights expression languages (RELs), like MPEG-21 REL [3] or ODRL [4],
allow declaring in a machine readable format which rights are given to whom
and under which conditions. If these rights expressions are to govern a computer
system giving conditional access to the resources, the term policy is preferred.
Computer access control mechanisms might govern the access to Linked Data re-
sources, based on the context, the user credentials and established access control
policies, possibly written in languages like XACML [5].
Both RELs and policy languages represent the same kind of information
(which actions a user can do with a certain resource), in a common underlying
model that has been manifested in the different existing languages. This abstrac-
tion might be made explicit as an Ontology Design Pattern (ODP) [6]: ODPs are
known modelling structures applied to recurrent problems, regarded as good so-
lutions in ontology design, and having a pattern for rights declaration may be of
interest in many different contexts. While [7] proposes such an explicit pattern,
this paper revolves about the existing rights declaration languages, abstracting
their commonalities and differences, assessing its adequacy for Linked Data, and
postulating that rights expressions for RDF should be manifested also in RDF
supported by a lightweight ontology and known vocabularies.
⋆ This research is supported by the Spanish Ministry of Science and Innovation through
a Juan de la Cierva fellowship and the project BabelData (TIN2010-17550).
2 Authors Suppressed Due to Excessive Length
2 Licensing languages
2.1 XML based Rights Expression Languages
Several rights expression languages have been defined since the late nineties,
having been applied in different contexts. This section examines the most no-
table of them (MPEG-21 REL, ODRL), as well as the policy language XACML.
Other XML-based languages, similar in nature or form are METSRights[8] as
the standard of the Library of the Congress to preserve and transmit digital
objects, or TVAnytime RMPI [9] in the audiovisual industry.
The MPEG-21 REL (ISO/IEC 21000-5) license is a XML document whose
hierarchical nature is reflected in Fig. 1(a). Each box in the figure represents an
XML element, enclosed in its parent element. The root element is the license,
comprising one or more grants given by an identified issuer. Each of the grants,
allows executing one or more rights against a resource by a principal, subject
to certain conditions. The actual rights (play, print, etc.) are defined in profiles
and further catalogued in a Rights Data Dictionary, as well as the conditions,
which can specify a price, different payment forms, a territory or a period during
which the grant holds, etc. An authorization mechanism is defined to validate if
a user request is backed by a proper license whose conditions are met.
The Open Digital Rights Language (ODRL) is a rights expression lan-
guage able to express permissions, prohibitions, obligations and assertions. It
was created in 2000 when DRM (Digital Rights Management) systems were
burgeoning, and in 2012 the latest specification (version 2.0) has been released.
Under different forms, it has been implemented in cell telephones (Open Mobile
Alliance DRM), in the eBook publishing industry and in the news rights man-
agement. ODRL is defined with an abstract core model plus profiles with the
specific vocabulary of particular domains, and it can be serialized as XML. In its
version 2.0, policy is the root element (Fig. 1(b)) and it can include permissions
or prohibitions. A permission allows a particular action to be executed on a re-
lated asset by a particular party, conditioned to some duties. The prohibition is
expressed in similar terms and it can be limited by constraints. These elements
can be combined to represent offers, agreements, requests or privacy settings.
Licensing with a XACML policy. XACML (Xtensible Access Control
Markup Language) is a general-purpose XML policy language, able to declare
attribute based access control policies to resources. The most important element
in XACML is also the policy (Fig. 1(c)), which is defined with a collection of
rules, obligations and a target to determine if the policy applies. Policies can
be combined following predefined algorithms. Each rule is composed of a target,
a condition and an effect (permit or deny). The target is made up of subjects
(entities requesting access), resources (data, services or system components) and
actions (the type of access requested on the resource). An environment provides
context information. Subjects, resources, actions and context have attributes
whose values are compared to the values in policies to decide the authorization.
Comparison of MPEG-21 REL, ODRL and XACML. Beyond the ap-
parent differences between these expression languages, it is possible to abstract
Licensing Patterns for Linked Data 3
Rules
Target
Action
Subject
Resource
Conditions
Effect
License
Grants
Right
Principal
Resource
Conditions
Issuer
Permission
Constraint
Policy
Action
Asset
Party
Duty
Prohibition
(a) MPEG-21 REL (b) ODRL2.0 (c) XACML
Target
Policy
Fig. 1.Main elements in a MPEG-21 REL license, and an ODRL and a XACML policy
some parallel concepts. The main XML element in MPEG-21 REL is license,
and policy in ODRL and XACML. They are equivalent in meaning and they can
contain, in any of the three cases, a set of permissions or prohibitions. These are
called permission / prohibition in ODRL, rule in XACML (duly attributed to de-
termine whether they permit or deny) and grants in MPEG-21 REL (which can-
not declare bans). This second-level element groups the authorized/prohibited
action: who does what over which resource. Actors take different names across
the languages (subject, party, issuer, principal) as well as actions (right, action)
and resources (also termed assets). Finally, the conditions in MPEG-21 REL or
XACML are equivalent to the duties and constraints in ODRL.
2.2 Ontologies capable of expressing Rights Expressions
There have been other attempts at least from the academia to build RELs at a
semantic level enabling reasoning like KAoS, Ponder or Rei [11]. LicenseScript
[10] was based in Logic Programming and had a materialization in Prolog, while
the CopyrightOntology1, OntologyX2 and the Copyright Registry3 were specified
in OWL. Although they propose solid models, none of them has a significative
community of users behind. Moreover, their design was done before the Linked
Data paradigm had gained spread, and they lack connectivity with other pieces
of data in the web. This section describes in more detail the most acknowledged
vocabulary (ccREL4), the MPEG-21 Media Value Chain Ontology5 (MVCO)
and the Web Access Control6 vocabulary (WAC).
The Creative Commons Rights Exprsesion Language (ccREL) can
represent Creative Commons licenses’ information using RDF. The main two
classes are Work and License, each of them having possibly attributes. The
1 http://rhizomik.net/html/ontologies/copyrightonto/
2 http://www.rightscom.com/Default.aspx?tabid=1067
3 ttp://semanticcopyright.org
4 http://wiki.creativecommons.org/CC REL
5 http://dmag.ac.upc.edu/ontologies/mvco/
6 http://www.w3.org/wiki/WebAccessControl
4 Authors Suppressed Due to Excessive Length
license permits, requires or prohibits actions (these terms being properties re-
lating the license to a set of limited and non-extendable rights, requirements
and bans). The actions in ccREL reflect the basic rights reflected in intellectual
property law, and common to almost any jurisdiction: reproduction (making
copies), distribution (publication of a copy of the work) and derivativeWorks
(publication of derived versions of the original work). Permissions can require a
notice, an attribution, etc. The prohibitions and the requirements, however, are
those particular of the Creative Commons licenses and lack the generality of the
permissions.
The MPEG-21 MVCO (ISO/IEC 21000-19) represents the intellectual
property entities along a value chain, and it defines an abstract model for grant-
ing permissions. It is also used by the Media Contract Ontology, in the stan-
dardization path to become the formal language to represent contracts handling
audiovisual contents and the rights thereof. In MVCO, a permission is given by
a user so that another user can execute an action over an IPEntity (object of
intellectual property including the original work and its transformations). The
permission can be conditioned to one or more facts to actually hold. Actual
users, permissions and intellectual property entities are instances of the respec-
tive classes.
The Web Access Control (WAC) vocabulary permits expressing who is
authorized to access to web resources through the so called access control lists
(ACL). ACLs declare the agents and their access modality (limited to read, write,
access, append and control) to InformationResources. WAV is simple (hardly a
dozen of classes and properties) yet in use in important services as in data.fm
or OpenLink Data Spaces7.
Comparison of ccREL, MPEG-21 MVCO and WAC. The presented
ontologies, capable of representing rights and authorizations, have similar ele-
ments. The concepts of license (ccREL), permission (MVCO) and authorization
(WAC) are equivalent, and they grant a permission (ccREL) an access (WAC) or
the right to execute an action (MVCO) on a given work, informationalResource
or IPEntity respectively by an agent (WAC) or a user (MVCO). Unlike the rest
of the mentioned languages, ccREL cannot express a licensee, and instead, each
policy applies for the public in general. It cannot declare prohibitions (useful for
example to restate a copyright ownership), nor conditions beyond those found
in Creative Commons licenses. In particular, this constrains the use of ccREL
for offers of non-open content where representing a price is needed.
3 A pattern for licensing Linked Data
The commonalities between the six analyzed rights expression languages, either
in XML or RDF, revolve about the n-ary relation that exists among a resource,
its rightsholder, another user (or the public in general), the deontic category
(permission, obligation, prohibition) and an action conditioned to some require-
ments. The tree structure of XML languages naturally includes these elements
7 http://ods.openlinksw.com/wiki/ODS/
Licensing Patterns for Linked Data 5
under a license node, but the representation as RDF –the natural one for licens-
ing Linked Data resources like RDF datasets or mappings– requires adopting
the solution of the n-ary relation pattern8, having a central entity related to the
others and qualifying the n-ary relation itself (qualified relation pattern9).
The new breed of vocabularies for Linked Data rights declaration like LiMO10,
L4LOD11 or ODRS12 have paved the way towards an acknowledged set of terms
found in existing open licenses. If interlinked, properly extended and articulated
as in the model discussed before, the representation of both existing licenses and
custom-taylored rights expressions will be possible, not only in open but also in
payment-based scenarios. While new tools for creating, evaluating and reasoning
on rights expressions are needed, an ecosystem of entities creating, brokering and
consuming open and proprietary Linked Data assets would benefit from a clear
rights expression model in harmony with the mature rights expression languages
which already share their essential features.
References
1. Bizer, C., Heath, T., Berners-Lee, T.: Linked data-the story so far. Int. J. on Se-
mantic Web and Information Systems, vol. 5, no. 3, pp. 1-–22 (2009)
2. Rodr´ıguez-Doncel, V., Go´mez-Pe´rez, A., and Mihindukulasooriya, N.: Rights dec-
laration in Linked Data. in Proc. of the 3rd Int. Workshop on Consuming Linked
Data. (2013)
3. ISO/IEC 21000-5:2004, Information Technology Multimedia Framework Part 5:
Rights Expression Language, ISO/IEC (2004)
4. Ianella, R., Guth, S., Paehler, D. and Kasten, A.: ODRL Version 2.0 Core Model,
W3C Community Group Final Specification (2012)
5. Moses, T.: Extensible access control markup language (XACML) version 2.0., OASIS
Standard (2005)
6. Gangemi, A. and Presutti, V.: Ontology Design Patterns. Handbook on Ontologies
(2nd ed.) Springer. Int. Handbooks on Information Systems (2009)
7. Rodr´ıguez-Doncel, V., Sua´rez-Figueroa, M. C., Go´mez-Pe´rez, A., and Poveda, M.:
License Linked Data Resources Pattern. in Proc.of the 4th Int. Workshop on On-
tology Patterns (to appear) (2013)
8. McDonough, J. P.: METS: standardized encoding for digital library objects. Inter-
national journal on digital libraries, 6(2), 148-158 (2006)
9. ETSI TS 102 822-5 Broadcast and On line Services. Part 5: Rights Management
and Protection Information for Broadcast Applications.Technical report, European
Telecommunications StandardsInstitute (2005)
10. Cheun Ngen Chong et al. Licensescript: A novel digital rights language and its
semantics. Int. conf. on Web Delivering of Music (2003)
11. Tonti, G., Bradshaw, J. M., Jeffers, R., Montanari, R., Suri, N. and Uszok, A.:
Semantic Web languages for policy representation and reasoning: A comparison of
KAoS, Rei, and Ponder. In ISWC 2003, pp. 419-437. Ed. Springer (2003)
8 http://www.w3.org/TR/swbp-n-aryRelations/
9 http://patterns.dataincubator.org/book/qualified-relation.html
10 http://data.opendataday.it/LiMo
11 http://ns.inria.fr/l4lod/v2/l4lod v2.htm
12 http://schema.theodi.org/odrs/


http://oa.upm.es/30123/1/INVE_MEM_2013_163178.pdf

Licensing patterns for Linked Data

Abstract

Similar works

Full text

Available Versions

Archivo Digital UPM

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid