Sebastian Speiser

Integrating linked data and services with linked data services

A sizable amount of data on the Web is currently available via Web APIs that expose data in formats such as JSON or XML. Combining data from different APIs and data sources requires glue code which is typically not shared and hence not reused. We propose Linked Data Services (LIDS), a general, formalised approach for integrating dataproviding services with Linked Data, a popular mechanism for data publishing which facilitates data integration and allows for decentralised publishing. We present conventions for service access interfaces that conform to Linked Data principles, and an abstract lightweight service description formalism. We develop algorithms that use LIDS descriptions to automatically create links between services and existing data sets. To evaluate our approach, we realise LIDS wrappers and LIDS descriptions for existing services and measure performance and effectiveness of an automatic interlinking algorithm over multiple billions of triples.

Data-Fu: a language and an interpreter for interaction with read/write linked data

An increasing amount of applications build their functionality on the utilisation and manipulation of web resources. Consequently REST gains popularity with a resource-centric interaction architecture that draws its flexibility from links between resources. Linked Data offers a uniform data model for REST with self-descriptive resources that can be leveraged to avoid a manual ad-hoc development of web-based applications. For declaratively specifying interactions between web resources we introduce Data-Fu, a lightweight declarative rule language with state transition systems as formal grounding. Data-Fu enables the development of data-driven applications that facilitate the RESTful manipulation of read/write Linked Data resources. Furthermore, we describe an interpreter for Data-Fu as a general purpose engine that allows to perform described interactions with web resources by orders of magnitude faster than a comparable Linked Data processor.

Taking the LIDS off data silos

LInked Data Services (LIDS) denote the integration of data-providing services and Linked Data. LIDS are parameterised and formally described web resources which return RDF when dereferenced via HTTP. In this paper we present a general method for creating Linked Data Services; LIDS consist of data access interface conventions that are compatible to Linked Data principles and a lightweight formal description model. Our approach is based on established Web standards including HTTP, RDF and SPARQL. Additionally, we announce several LIDS that we have created from existing real-life services, unlocking vast amounts of triples to the Web of Data.

ShareAlike your data: self-referential usage policies for the semantic web

Numerous forms of policies, licensing terms, and related conditions are associated with Web data and services. A natural goal for facilitating the reuse and re-combination of such content is to model usage policies as part of the data so as to enable their exchange and automated processing. This paper thus proposes a concrete policy modelling language. A particular difficulty are self-referential policies such as Creative Commons ShareAlike, that mandate that derived content is published under some license with the same permissions and requirements. We present a general semantic framework for evaluating such recursive statements, show that it has desirable formal properties, and explain how it can be evaluated using existing tools. We then show that our approach is compatible with both OWL DL and Datalog, and illustrate how one can concretely model self-referential policies in these languages to obtain desired conclusions.

Semantic Annotations for WS-Policy

WS-Policy is a standard to express requirements and capabilities in Web service systems. Policies are based on domain-specific assertions. In this paper we present a lightweight approach to semantic annotations of policy assertions. The approach allows matching of requirements and capabilities based not only on the syntactical representation of their corresponding assertions but also on their semantic meaning. Besides vocabulary mismatches our approach can also handle granularity mismatches, e.g. if two capabilities in combination satisfy a single requirement. We present a validation of our approach consisting of a performance evaluation and the realization of a use case, both based on our implementation of the semantic policy matching algorithm. We furthermore show the advantages of our approach compared to existing related work.

Formation of Service Value Networks for Decentralized Service Provisioning

The provisioning of complex services requires tight collaboration between diverse service providers and their customers harmonizing supply and demand chains to a highly flexible, dynamic and decentralized service value network. Peers in such a network autonomously delegate (sub-)tasks which cannot be done efficiently by themselves to other more suitable peers in their community. In this paper, we propose an architecture for such service communities that features decentralized service provisioning based on current Web technologies. In this context, we present an algorithm for efficient service value network formation and show by means of a simulation that sufficiently sized service networks can fulfill practically all customer requests. When compared to the optimal (central) case, there is a modest price increase for the customers but the overall welfare decreases only insignificantly.

Web technologies and privacy policies for the Smart Grid

The Smart Grid aims at making the current electricity grid more efficient, featuring an IT-layer that includes communication flows between a multitude of stakeholders. Its infrastructure is likely to be integrated with other IT-based systems. We argue that in order to enable the integration between already existing large-scale information networks (e.g., the Internet or the Web) and newly developed IT infrastructures such as Smart Cities, means for machine-understandable representation of data are required. Since these “smart” systems will exchange large volumes of highly sensitive data (billing and personal data), users should have the ability to specify their intent on how their data can be shared. Thus, systems require built-in mechanisms for protecting data. In this paper, we outline a Smart Grid architecture based on Semantic Web (Linked Data) technologies, and present mechanisms to allow for automated access control and enforcement of privacy rights on a technical level.

A self-policing policy language

Formal policies allow the non-ambiguous definition of situations in which usage of certain entities are allowed, and enable the automatic evaluation whether a situation is compliant. This is useful for example in applications using data provided via standardized interfaces. The low technical barriers of integrating such data sources is in contrast to the manual evaluation of natural language policies as they currently exist. Usage situations can themselves be regulated by policies, which can be restricted by the policy of a used entity. Consider for example the Google Maps API, which requires that applications using the API must be available without a fee, i.e. the applications policy must not require a payment. In this paper we present a policy language that can express such constraints on other policies, i.e. a self-policing policy language. We validate our approach by realizing a use case scenario, using a policy engine developed for our language.

Semantic Usage Policies for Web Services

Web Services provide standardized interfaces for accessing software systems and data sources over the Internet. Semantic descriptions of Web Services help to automate the discovery and invocation of new services and their integration into existing applications. However not all services are freely available for every purpose and not all data is in the public domain. Usage policies describe the terms and conditions under which services and data can be used. Current approaches to semantic Web Service description are mostly focused on functional properties and quality attributes, and do not cover usage policies. We plan to develop a formal language for usage policies with clearly defined semantics that relies on ontologies for representing domain specific terms. We will also extend service discovery and ranking algorithms to incorporate usage policies.

Usage policies for document compositions

The availability of contents and information as linked data or Web services, i.e. over standardized interfaces, fosters the integration and reuse of data. One common form of information integration is the creation of composed documents, e.g. in form of dynamic Web pages. Service and data providers restrict allowed usage of their resources and and link it to obligations, e.g. only non-commercial usage is allowed and requires an attribution of the provider. These terms and conditions are currently typically available in natural language which makes checking, if a document composition is compliant with the policies of the used services, a tedious task. In order to make it easier for users to adhere to these usage policies, we propose to formalize them, which enables policy-aware tools that support the creation of compliant compositions. In this paper we propose an OWL model of document compositions and show how it can be used together with the policy language AIR to build a policy-aware document composition platform. We furthermore present a use case and illustrate how it can be realized with our approach.