Efficiently pinpointing SPARQL query containments

Query containment is a fundamental problem in database research, which is relevant for many tasks such as query optimisation, view maintenance and query rewriting. For example, recent SPARQL engines built on Big Data frameworks that precompute solutions to frequently requested query patterns, are conceptually an application of query containment. We present an approach for solving the query containment problem for SPARQL queries – the W3C standard query language for RDF datasets. Solving the query containment problem can be reduced to the problem of deciding whether a sub graph isomorphism exists between the normalized algebra expressions of two queries. Several state-of-the-art methods are limited to matching two queries only, as well as only giving a boolean answer to whether a containment relation holds. In contrast, our approach is fit for view selection use cases, and thus capable of efficiently enumerating all containment mappings among a set of queries. Furthermore, it provides the information about how two queries’ algebra expression trees correspond under containment mappings. All of our source code and experimental results are openly available

On the estimation of cointegration models

Includes bibliographical referencesAvailable from British Library Document Supply Centre- DSC:DX221226 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Mycoplasmal mastitis in dairy herds

This paper addresses two main issues of the DOK system [15], that is the design of a framework for enforcing security policies and a secure architecture which implements such a framework. Federated security policies are expressed as logic-based expressions (called "aggregation constraints") specifying the different combinations of transactions that a user is not allowed to issue, either in single or multiple states of a federation. To enable efficient monitoring of aggregation constraints, state transition graphs are generated to model the different sub-computations of the constraints. Two marking techniques, namely LMT (Linear Marking Technique) and ZMT (Zigzag Marking Technique), are proposed to detect violations of federated security policies. To enable an effective enforcement of security policies, we designed a secure DOK architecture using specialised agents: (i) coordination agents allow the coordination of different federated activities, (ii) task agents perform specific tasks of th..