Linked Data and multimedia: the state of affairs

Linked Data is a way of exposing and sharing data as resources on the Web and interlinking them with semantically related resources. In the last three years significant amounts of data have been generated, increasingly forming a globally connected, distributed data space. For multimedia content, metadata are a key factor for efficient management, organization, and retrieval. However, the relationship between multimedia and Linked Data has been rarely studied, leading to a lack of mutual awareness and, as a consequence thereof, technological deficiencies. This article introduces the basic concepts of Linked Data in the context of multimedia metadata, and discusses techniques to generate, expose, discover, and consume Linked Data. It shows that a large amount of data sources exist, which are ready to be exploited by multimedia applications. The benefit of Linked Data in two multimedia-related applications is discussed and open research issues are outlined with the goal of bringing the research fields of multimedia and Linked Data closer together in order to facilitate mutual benefit.     

SESLDS: An Extension Scheme for Linked Data Sources Based on Semantically Enhanced Annotation and Reasoning

In the era of Big Data, users prefer to get knowledge rather than pages from Web. Linked Data, a rather new form of knowledge representation and publishing described by RDF, can provide a more precise and comprehensible semantic structure to satisfy the aforementioned requirement. Besides, as the standard query language for RDF data, SPARQL has become the foundation protocol of Linked Data querying. The core idea of RDF Schema (RDFS) is to extend upon RDF vocabulary and allow attachment of semantics to user defined classes and properties. However, RDFS cannot fully utilize the potential of RDF since it cannot express the implicit semantics between linked entities in Linked Data sources. To fill this gap, in this paper, we design a new semantic annotating and reasoning approach that can extend more implicit semantics from different properties. We firstly establish a well‐defined semantically enhanced annotation strategy for Linked Data sources. In particular, we present some new semantic properties for predicates in RDF triples and design a Semantic Matrix for Predicates (SM_P). We then propose a novel general Semantically Extended Scheme for Linked Data Sources (SES_LDS) to realize the semantic extension over the target Linked Data source through semantically enhanced reasoning. Lastly, based on the experimental analyses, we verify that our proposal has advantages over the initial Linked Data source and can return more valid results.     

Leveraging link pattern for entity-centric exploration over Linked Data

The increasing amount of Linked Data on the Web can be reused to facilitate numerous applications. One of the first steps is to explore these structured data to determine whether there is relevant information. Since an entity-centric model closely reflects the real world, it provides an intuitive way to explore Linked Data. However, large numbers of linked entities and high diversity of links between entities, often make it difficult for users to understand the overall structure, as well as find the entities of interest quickly for further exploration. In this paper, we present a link pattern discovery approach to facilitate entity exploration. Link patterns describe explicit and implicit relationships between entities and can be used to categorize linked entities. On top of link patterns, we construct a hierarchy to allow exploration of linked entities in a hierarchical multiscale fashion. To lighten users’ exploration burden further, we select top-k link patterns from hierarchy as navigation options. The proposed approach is implemented in a Linked Data browser called SView. We compare it with two conventional Linked Data browsers by conducting a task-based user study. The experiment results show that our approach provides effective support for entity exploration.     

Exploratory spatio-temporal analysis of linked statistical data

Publishing and sharing open government data in Linked Data format provides many opportunities in terms of data aggregation/integration and creation of information mashups. Statistical data, that contains various performance indicators and their evolution through time, is an example of data that can be used as the foundation for policy prediction, planning and adjustments, and can be re-used in different applications. However, due to Linked Data being relatively a new field, currently there is a lack of tools that enable efficient exploration and analysis of linked geospatial statistical datasets. Therefore, ESTA-LD (Exploratory Spatio-Temporal Analysis) tool was developed to address some of the Linked statistical Data management issues, such as crossing the statistical and the geographical dimensions, producing statistical maps, visualizing different measures, and comparing statistical indicators of different regions through time. This paper discusses the modeling approach that was adopted so that the published data conform to the established standards for representing statistical, spatial and temporal data in Linked Data format. The main contribution is related to the delivery of state-of-the-art open-source tools for retrieving, quality assessment, exploration and analysis of statistical Linked Data that is made available through a SPARQL endpoint.     

BioPW+:基于Linked Data的生物途径数据可视化系统

自Linked Data项目被提出以来,大量的开放关联数据被发布到语义Web上,这其中就包含了许多的生物途径数据集。为了使生物学家能够有效地利用这些开放的数据集,对基于Linked Data的生物途径数据可视化系统进行研究,提出了生物途径可视化模型和展示布局方案,并且采用标识符动态映射实现了多源生物途径数据的浏览,最终开发了基于Linked Data的生物途径数据查询可视化系统——BioPW+。该系统应用语义Web技术,依靠SPARQL查询来定位生物途径的基本信息,然后基于Open PHACTS平台获取生物途径元素的详细信息,最终Web界面采用力导向图布局、Sankey图布局对生物途径数据进行展示并提供多种交互操作。与已有的仅仅基于某一特定数据库的生物途径工具相比,BioPW+系统基于Linked Data,可以同时一次性展示多个数据集中的生物途径数据及与其相关的其他生物化学数据,极大节省了时间并增强了数据的完整性。     

Improving interoperability using vocabulary linked data

The concept of Linked Data has been an emerging theme within the computing and digital heritage areas in recent years. The growth and scale of Linked Data has underlined the need for greater commonality in concept referencing, to avoid local redefinition and duplication of reference resources. Achieving domain-wide agreement on common vocabularies would be an unreasonable expectation; however, datasets often already have local vocabulary resources defined, and so the prospects for large-scale interoperability can be substantially improved by creating alignment links from these local vocabularies out to common external reference resources. The ARIADNE project is undertaking large-scale integration of archaeology dataset metadata records, to create a cross-searchable research repository resource. Key to enabling this cross search will be the ‘subject’ metadata originating from multiple data providers, containing terms from multiple multilingual controlled vocabularies. This paper discusses various aspects of vocabulary mapping. Experience from the previous SENESCHAL project in the publication of controlled vocabularies as Linked Open Data is discussed, emphasizing the importance of unique URI identifiers for vocabulary concepts. There is a need to align legacy indexing data to the uniquely defined concepts and examples are discussed of SENESCHAL data alignment work. A case study for the ARIADNE project presents work on mapping between vocabularies, based on the Getty Art and Architecture Thesaurus as a central hub and employing an interactive vocabulary mapping tool developed for the project, which generates SKOS mapping relationships in JSON and other formats. The potential use of such vocabulary mappings to assist cross search over archaeological datasets from different countries is illustrated in a pilot experiment. The results demonstrate the enhanced opportunities for interoperability and cross searching that the approach offers.     

Challenges for the multilingual Web of Data

The Web has witnessed an enormous growth in the amount of semantic information published in recent years. This growth has been stimulated to a large extent by the emergence of Linked Data. Although this brings us a big step closer to the vision of a Semantic Web, it also raises new issues such as the need for dealing with information expressed in different natural languages. Indeed, although the Web of Data can contain any kind of information in any language, it still lacks explicit mechanisms to automatically reconcile such information when it is expressed in different languages. This leads to situations in which data expressed in a certain language is not easily accessible to speakers of other languages.The Web of Data shows the potential for being extended to a truly multilingual web as vocabularies and data can be published in a language-independent fashion, while associated language-dependent (linguistic) information supporting the access across languages can be stored separately. In this sense, the multilingual Web of Data can be realized in our view as a layer of services and resources on top of the existing Linked Data infrastructure adding (i) linguistic information for data and vocabularies in different languages, (ii) mappings between data with labels in different languages, and (iii) services to dynamically access and traverse Linked Data across different languages.In this article, we present this vision of a multilingual Web of Data. We discuss challenges that need to be addressed to make this vision come true and discuss the role that techniques such as ontology localization, ontology mapping, and cross-lingual ontology-based information access and presentation will play in achieving this. Further, we propose an initial architecture and describe a roadmap that can provide a basis for the implementation of this vision.     

一种数据采集与分析平台的研究与设计

随着互联网大数据技术的不断发展,网络数据采集技术成为热门的研究领域之一。基于Python语言下的数据采集功能库如Urllib、Requests、Selenium等模块效率低、易阻塞,并且目前的数据采集和分析平台都是独立的功能模块,没有形成闭环,用户体验差。为了解决上述问题,提出一种数据采集和分析平台,首先使用Scrapy框架完成数据采集,其次将采集到的数据通过Kettle工具进行数据清洗,再次,将处理好的结果存入MySQL 数据库,最后利用Flask框架,结合Echarts 技术搭建Web 系统,对数据分析结果进行可视化。以北京公交网站数据作为爬虫测试平台,通过对公交线路类型、公交路线等信息进行采集分析及结果展示,分析结果对城市公交的规划具有一定的指导意义,同时,平台具有稳定可靠、操作简单、实时性强等特点。     

Comparing data summaries for processing live queries over Linked Data

A growing amount of Linked Data??graph-structured data accessible at sources distributed across the Web??enables advanced data integration and decision-making applications. Typical systems operating on Linked Data collect (crawl) and pre-process (index) large amounts of data, and evaluate queries against a centralised repository. Given that crawling and indexing are time-consuming operations, the data in the centralised index may be out of date at query execution time. An ideal query answering system for querying Linked Data live should return current answers in a reasonable amount of time, even on corpora as large as the Web. In such a live query system source selection??determining which sources contribute answers to a query??is a crucial step. In this article we propose to use lightweight data summaries for determining relevant sources during query evaluation. We compare several data structures and hash functions with respect to their suitability for building such summaries, stressing benefits for queries that contain joins and require ranking of results and sources. We elaborate on join variants, join ordering and ranking. We analyse the different approaches theoretically and provide results of an extensive experimental evaluation.     

Instance matching benchmarks in the era of Linked Data

The goal of this survey is to present the state of the art instance matching benchmarks for Linked Data. We introduce the principles of benchmark design for instance matching systems, discuss the dimensions and characteristics of an instance matching benchmark, provide a comprehensive overview of existing benchmarks, as well as benchmark generators, discuss their advantages and disadvantages, as well as the research directions that should be exploited for the creation of novel benchmarks, to answer the needs of the Linked Data paradigm.     

Abstract,link, publish,exploit: An end to end framework for workflow sharing

Scientific workflows are increasingly used to manage and share scientific computations and methods to analyze data. A variety of systems have been developed that store the workflows executed and make them part of public repositories However, workflows are published in the idiosyncratic format of the workflow system used for the creation and execution of the workflows. Browsing, linking and using the stored workflows and their results often becomes a challenge for scientists who may only be familiar with one system. In this paper we present an approach for addressing this issue by publishing and exploiting workflows as data on the Web with a representation that is independent from the workflow system used to create them. In order to achieve our goal, we follow the Linked Data Principles to publish workflow inputs, intermediate results, outputs and codes; and we reuse and extend well established standards like W3C PROV. We illustrate our approach by publishing workflows and consuming them with different tools designed to address common scenarios for workflow exploitation.     

A systematic literature review of Linked Data‐based recommender systems

Recommender systems (RS) are software tools that use analytic technologies to suggest different items of interest to an end user. Linked Data is a set of best practices for publishing and connecting structured data on the Web. This paper presents a systematic literature review to summarize the state of the art in RS that use structured data published as Linked Data for providing recommendations of items from diverse domains. It considers the most relevant research problems addressed and classifies RS according to how Linked Data have been used to provide recommendations. Furthermore, it analyzes contributions, limitations, application domains, evaluation techniques, and directions proposed for future research. We found that there are still many open challenges with regard to RS based on Linked Data in order to be efficient for real applications. The main ones are personalization of recommendations, use of more datasets considering the heterogeneity introduced, creation of new hybrid RS for adding information, definition of more advanced similarity measures that take into account the large amount of data in Linked Data datasets, and implementation of testbeds to study evaluation techniques and to assess the accuracy scalability and computational complexity of RS. Copyright © 2015 John Wiley & Sons, Ltd.     

Adding value to Linked Open Data using a multidimensional model approach based on the RDF Data Cube vocabulary

Most organisations using Open Data currently focus on data processing and analysis. However, although Open Data may be available online, these data are generally of poor quality, thus discouraging others from contributing to and reusing them. This paper describes an approach to publish statistical data from public repositories by using Semantic Web standards published by the W3C, such as RDF and SPARQL, in order to facilitate the analysis of multidimensional models. We have defined a framework based on the entire lifecycle of data publication including a novel step of Linked Open Data assessment and the use of external repositories as knowledge base for data enrichment. As a result, users are able to interact with the data generated according to the RDF Data Cube vocabulary, which makes it possible for general users to avoid the complexity of SPARQL when analysing data. The use case was applied to the Barcelona Open Data platform and revealed the benefits of the application of our approach, such as helping in the decision-making process.     

LinkMF: 结合Linked Data的协同过滤推荐算法

协同过滤(CF)是推荐系统中应用最为广泛的推荐算法之一,然而数据稀疏性和冷启动问题是协同过滤方法的两个主要挑战。由于Linked Data整合了关于实体的丰富且结构化的特征,可以作为额外的信息源来缓解以上两种挑战。该文中我们首次提出了结合Linked Data改进CF推荐算法,基于矩阵分解提出了一种新的CF模型——LinkMF,在保证推荐准确度的基础上利用Linked Data缓解数据稀疏性和冷启动问题。首先,我们从Linked Data中抽取项目的特征表示并为项目建模;然后提出新的相似度度量方法计算项目相似度;最后利用项目相似度约束和指导MF分解过程产生推荐。在MovielLens和YAGO标准数据集上的大量实验结果表明,LinkMF优于现有的一些CF方法,特别在缓解数据稀疏性和冷启动问题上取得很好地效果。     

基于数据库集群的海量 RDF 数据联合查询系统的研究与实现

随着语义网的快速发展,为了实现科学数据的共享,越来越多的科学数据被加工发布为关联数据,进而应用于关联查询和关联发现。针对大规模关联数据的管理,本文通过构建 RDF 数据库集群来存储海量数据,设计了基于 SPARQL 端点的联合查询系统来解决用户跨机器透明查询的问题,分析了存储策略和联合查询系统的查询处理相关技术。实际运行表明,本平台易于集成使用,可以实现大规模 RDF 数据的可扩展性存储和有效查询。