Cloud computing solutions continue to grow increasingly popular both in research and in the commercial IT industry. With this popularity comes ever increasing challenges for the cloud computing service providers. Semantic web is another domain of rapid growth in both research and industry. RDF datasets are becoming increasingly large and complex and existing solutions do not scale adequately. In this paper, we will detail a scalable semantic web framework built using cloud computing technologies. We define solutions for generating and executing optimal query plans. We handle not only queries with Basic Graph Patterns (BGP) but also complex queries with optional blocks. We have devised a novel algorithm to handle these complex queries. Our algorithm minimizes binding triple patterns and joins between them by identifying common blocks by algorithms to find sub graph isomorphism and building a query plan utilizing that information. We utilize Hadoop's MapReduce framework to process our query plan. We will show that our framework is extremely scalable and efficiently answers complex queries.

Cloud computing is rapidly growing in popularity as a solution for processing and retrieving huge amounts of data over clusters of inexpensive commodity hardware. The most common data model utilized by cloud computing software is the NoSQL data model. While this data model is extremely scalable, it is much more efficient for simple retrievals and scans than for the complex analytical queries typical in a relational database model. In this paper, we evaluate emerging cloud computing technologies using a representative use case. Our use case involves analyzing telecommunications logs for performance monitoring and quality assurance. Clearly, the size of such logs is growing exponentially as more devices communicate more frequently and the amount of data being transferred steadily increases. We analyze potential solutions to provide a scalable database which supports both retrieval and analysis. We will investigate and analyze all the major open source cloud computing solutions and designs. We then choose the most applicable subset of these technologies for experimentation. We provide a performance evaluation of these products, and we analyze our results and make recommendations. This paper provides a comprehensive survey of technologies for scalable data processing and an in-depth performance evaluation of these technologies.

There are many significant research projects focused on providing semantic web repositories that are scalable and efficient. However, the true value of the semantic web architecture is its ability to represent meaningful knowledge and not just data. Therefore, a semantic web knowledge base should do more than retrieve collections of triples. We propose RDFKB (Resource Description Knowledge Base), a complete semantic web knowledge case. RDFKB is a solution for managing, persisting and querying semantic web knowledge. Our experiments with real world and synthetic datasets demonstrate that RDFKB achieves superior query performance to other state-of-the-art solutions. The key features of RDFKB that differentiate it from other solutions are: 1) a simple and efficient process for data additions, deletions and updates that does not involve reprocessing the dataset; 2) materialization of inferred triples at addition time without performance degradation; 3) materialization of uncertain information and support for queries involving probabilities; 4) distributed inference across datasets; 5) ability to apply alignments to the dataset and perform queries against multiple sources using alignment. RDFKB allows more knowledge to be stored and retrieved; it is a repository not just for RDF datasets, but also for inferred triples, probability information, and lineage information. RDFKB provides a complete and efficient RDF data repository and knowledge base.

Semantic web is an emerging area to augment human reasoning. Various technologies are being developed in this arena which have been standardized by the World Wide Web Consortium (W3C). One such standard is the Resource Description Framework (RDF). Semantic web technologies can be utilized to build efficient and scalable systems for Cloud Computing. With the explosion of semantic web technologies, large RDF graphs are common place. This poses significant challenges for the storage and retrieval of RDF graphs. Current frameworks do not scale for large RDF graphs and as a result do not address these challenges. In this paper, we describe a framework that we built using Hadoop to store and retrieve large numbers of RDF triples by exploiting the cloud computing paradigm. We describe a scheme to store RDF data in Hadoop Distributed File System. More than one Hadoop job (the smallest unit of execution in Hadoop) may be needed to answer a query because a single triple pattern in a query cannot simultaneously take part in more than one join in a single Hadoop job. To determine the jobs, we present an algorithm to generate query plan, whose worst case cost is bounded, based on a greedy approach to answer a SPARQL Protocol and RDF Query Language (SPARQL) query. We use Hadoop's MapReduce framework to answer the queries. Our results show that we can store large RDF graphs in Hadoop clusters built with cheap commodity class hardware. Furthermore, we show that our framework is scalable and efficient and can handle large amounts of RDF data, unlike traditional approaches.

As the semantic web grows in popularity and enters the mainstream of computer technology, RDF (Resource Description Framework) datasets are becoming larger and more complex. Advanced semantic web ontologies, especially in medicine and science, are developing. As more complex ontologies are developed, there is a growing need for efficient queries that handle inference. In areas such as research, it is vital to be able to perform queries that retrieve not just facts but also inferred knowledge and uncertain information. OWL (Web Ontology Language) defines rules that govern provable inference in semantic web datasets. In this paper, we detail a database schema using bit vectors that is designed specifically for RDF datasets. We introduce a framework for materializing and storing inferred triples. Our bit vector schema enables storage of inferred knowledge without a query performance penalty. Inference queries are simplified and performance is improved. Our evaluation results demonstrate that our inference solution is more scalable and efficient than the current state-of-the-art. There are also standards being developed for representing probabilistic reasoning within OWL ontologies. We specify a framework for materializing uncertain information and probabilities using these ontologies. We define a multiple vector schema for representing probabilities and classifying uncertain knowledge using thresholds. This solution increases the breadth of information that can be efficiently retrieved.

There is a growing need for efficient and scalable semantic web queries that handle inference. There is also a growing interest in representing uncertainty in semantic web knowledge bases. In this paper, we present a bit vector schema specifically designed for RDF (Resource Description Framework) datasets. We propose a system for materializing and storing inferred knowledge using this schema. We show experimental results that demonstrate that our solution drastically improves the performance of inference queries. We also propose a solution for materializing uncertain information and probabilities using multiple bit vectors and thresholds.

RDFKB (Resource Description Framework Knowledge Base) is a solution for managing, persisting and querying semantic web knowledge. RDFKB provides a flexible data management schema that allows additions, deletions, and updates at all levels in the data model. RDFKB also supports 1) knowledge inference, 2) provenance and lineage, 3) probabilities and uncertainty reasoning, 4) trust factors, 5) dataset linkage and ontology alignment. We will show through a variety of use cases and experiments that RDFKB enables each of these tasks. We will also show that RDFKB outperforms all other semantic web repositories through experiments using 26 queries against 2 accepted benchmark datasets.

RDFKB (Resource Description Framework Knowledge Base) is a relational database system for RDF datasets which supports inference and knowledge management. Significant research has addressed improving the performance of queries against RDF datasets. Generally, this research has not addressed queries against inferred knowledge. Solutions which do support inference queries have done so as part of query processing. Ontologies define the rules that govern inference for RDF datasets. These inference rules can be applied to RDF datasets to derive additional facts through methods such as subsumption, symmetry and transitive closure. We propose a framework that supports inference at data storage time rather than as part of query processing. The dataset is increased to include all knowledge whether explicitly specified or derived through inference with a negligible overhead. Queries against inferred data are simplified, and performance is increased.