Data replication and update propagation in XML P2P data management systems

XML P2P data management systems are P2P systems that use XML as the underlying data format shared between peers in the network. These systems aim to bring the benefits of XML and P2P systems to the distributed data management field. However, P2P systems are known for their lack of central control and high degree of autonomy. Peers may leave the network at any time at will, increasing the risk of data loss. Despite this, most research in XML P2P systems focus on novel and efficient XML indexing and retrieval techniques. Mechanisms for ensuring data availability in XML P2P systems has received comparatively little attention. This project attempts to address this issue. We design an XML P2P data management framework to improve data availability. This framework includes mechanisms for wide-spread data replication, replica location and update propagation. It allows XML documents to be broken down into fragments. By doing so, we aim to reduce the cost of replicating data by distributing smaller XML fragments throughout the network rather than entire documents. To tackle the data replication problem, we propose a suite of selection and placement algorithms that may be interchanged to form a particular replication strategy. To support the placement of replicas anywhere in the network, we use a Fragment Location Catalogue, a global index that maintains the locations of replicas. We also propose a lazy update propagation algorithm to propagate updates to replicas. Experiments show that the data replication algorithms improve data availability in our experimental network environment. We also find that breaking XML documents into smaller pieces and replicating those instead of whole XML documents considerably reduces the replication cost, but at the price of some loss in data availability. For the update propagation tests, we find that the probability that queries return up-to-date results increases, but improvements to the algorithm are necessary to handle environments with high update rates

The statistical analysis of complex sampling data

>Magister Scientiae - MScMost standard statistical techniques illustrated in text books assume that the data are collected from a simple random sample (SRS) and hence are independently and identically distributed (i.i.d.). In reality, data are often sourced through complex sampling (CS) designs, with a combination of stratification and clustering at different levels of the design. Consequently, the CS data are not i.i.d. and sampling weights that are developed over different stages, are calculated and included in the analysis of this data to account for the sampling design. Logistic regression is often employed in the modelling of survey data since the response under investigation typically has a dichotomous outcome. Furthermore, since the logistic regression model has no homogeneity or normality assumptions, it is appealing when modelling a dichotomous response from survey data. This research considers the comparison of the estimates of the logistic regression model parameters when the CS design is accounted for, i.e. weighting is present, to when the data are modelled using an SRS design, i.e. no weighting. In addition, the standard errors of the estimators will be obtained using three different variance techniques, viz. Taylor series linearization, the jackknife and the bootstrap. The different estimated standard errors will be used in the calculation of the standard (asymptotic) interval which will be compared to the bootstrap percentile interval in terms of the interval coverage probability. A further level of comparison is obtained when using only design weights to those obtained using calibrated and integrated sampling weights. This simulation study is based on the Income and Expenditure Survey (IES) of 2005/2006. The results showed that generally when weighting was used the estimators performed better as opposed to when the design was ignored, i.e. under the assumption of SRS, with the results for the Taylor series linearization being more stable

A framework and toolkit for the collection and analysis of QoS statistics for voice traffic in Next Generation Networks

The multi-service, multi-architecture nature of NGNs is so complex that the management of services, in addition to networks, emerges as a research challenge. Despite QoS limitations, VoIP (as opposed to VoATM), dominates the Internet and enterprise markets, and is evolving to handle the carrier space. This paper presents a strategy that abstracts QoS away from both VoATM and VoIP in order to manage voice QoS in an NGN environment.Telkom, Siemens, THRI

Investigation into metal contamination of the Berg River, Western Cape, South Africa

A recent decline in water quality of the Berg River, Western Cape, South Africa, has led to the investigation into the degree of metal pollution in the river system. This study was conducted over a period of one year, from May 2004 to May 2005. The nitric acid digestion technique was used to extract metals from water, sediment and biofilm samples collected at various points (Site A . agricultural area, Site B . informal settlement and Site C . Newton pumping station) along the Berg River. Metal concentrations were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The highest mean metal concentrations recorded were as follows; water samples, 6 mgE.-1 for Al, 14.6 mgE.-1 for Fe and 18.8 mg..-1 for Mn; sediment samples, 17 448.8 mgEkg-1 for Al and 26 473.3 mgEkg-1 for Fe; biofilm samples, 876.8 mgE.-1 for Al and 1 017.5 mgE.-1 for Fe. The increased availability, or noteworthy incidence of Al and Fe, could be due to the leaching of metals into the river water from waste and household products associated with the informal settlement and the subsequent settling on sediment. No guidelines were available for metals in biofilms. The highest recorded concentrations in water were for Site C (agricultural area). Recorded concentrations in water fluctuated throughout the study period for most of the metals analysed, but Al and Fe were consistently above the recommended guidelines as stipulated by the Department of Water Affairs and Forestry and the Canadian Council of Ministers of the Environment

Comparison of Degradation Gradients of a Conventional vs a High Pressure Grazing System

Grazing management is important for general ecosystem health and sustainable livestock production. Historic grazing practices caused grassland degradation. Regenerative grazing practices can improve soil and plant health. This study aimed to determine if a high pressure grazing approach, in fact improves soil and plant health, compared to a conventional grazing system. A degradation gradient (away from watering places) approach were followed. The study site is situated in the Kalahari bushveld bioregion of the North West province of South Africa. Two adjacent farms were selected, one practicing a conventional four camp rotational grazing system, and the other practicing high pressure grazing with 50 camps in a radial layout. Plant species composition and soil properties (carbon, root biomass, minerals) were measured at three increasing distances away from the water. The results indicated an increase in veld condition away from the water in the conventional system, while the veld condition decreased slightly in the high pressure grazing system. Soil properties for the conventional system did not vary much at increasing distances away from the water. At the high pressure system, soil health was slightly better closer to the water. Soil health was generally better at the high pressure system, than at the conventional system. These results indicate that a high pressure grazing approach, where high animal numbers graze an area, evenly, for a short period of time, followed by a long resting period, is more beneficial to plant and soil health, than a conventional grazing approach where lower animal numbers, graze bigger areas for a longer time period. In the Kalahari bushveld of the North West province of South Africa, high pressure grazing systems has the potential to regenerate soil- and plant health

The Comparative Effects of Short Duration, High Density and Conventional, Rotational Grazing on Different Soil, Vegetation and Animal Parameters in Dry and Mesic Grasslands of South Africa

Short duration, high density grazing is a grazing management strategy that incorporates the rotation of large livestock herds, often at double or triple the normal prescribed stocking densities of the specific area. It is claimed that this type of grazing management can improve rangeland health by improving soil and vegetation condition, and subsequently influencing animal performance. Regardless of the scarcity of scientific evidence validating these claims, the change from conventional rotational grazing systems to short duration, high density grazing systems is on the increase in South Africa. This study aims to assess these claims, through the quantification of various rangeland vegetation and soil health, and livestock performance parameters under both conventional rotational and short duration, high density grazing systems. The study will be conducted through fence line contrast studies, whereby neighbouring farms, one practising short duration, high density grazing and the other conventional, rotational grazing, will be assessed. Soil parameters to be investigated will include soil physical (compaction) and chemical (pH, carbon, nitrogen, exchangeable cations) characteristics, whereas vegetation characteristics will include species composition, production, vigour and quality. In addition, animal performance will be measured as body condition and calving rate. This project has the potential to provide objective, scientifically based information regarding some of the controversies revolving around short duration, high density grazing, as well as contribute to the sustainability and economic viability of livestock production in Southern Africa

Being ill with the disease of schizophrenia

This study is an ethnographic exploration of deinstitutionalised schizophrenics in Montreal. The focus of this paper is how schizophrenics and their primary caregivers have come to understand and reinterpret schizophrenia in an era of post-institutionalisation. The emphasis of this paper is on how Quebec's virage ambulatoire has seen the shift in responsibility for the psychiatrically ill from psychiatrists to community care workers and the schizophrenics themselves. In addition to the historical development of institutionalisation and deinstitutionalisation this work includes a description of the places schizophrenics have come to rely upon in the wake of closed asylum beds. Other issues to be addressed are; the conflict between objective disease and subjective illness; agency, psychiatric non-compliance and social non-conformity; concepts of wellness and chronic illness; and the utility of a psychiatric diagnosis in augmenting benefits and accessing services. Because of the exploratory nature of the study, conclusions are formulated in terms of further work to be accomplished and different epistemological tools to be developed to better understand the situation

Investigation into the metal contamination of the Plankenburg and Diep Rivers, Western Cape, South Africa

Metal contamination in the Plankenburg and Diep Rivers (Western Cape) was investigated over a 12 and 9 month period, respectively. Aluminium (Al), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) concentrations were determined using the nitric acid digestion method and analysed by inductively coupled plasma atomic emission spectrometry (ICP-AES). For both rivers the Al and Fe concentrations were higher than that for all the other metals analysed for in sediment and water samples. The highest concentrations recorded in the Plankenburg River were 13.6 mgE.-1 (water . Week 18, Site B) and 15 018 mgEkg-1 (sediment . Week 1, Site C) for Al, and 48 mgE.-1 (water . Week 43, Site A) and 14 363.8 mgEkg-1 (sediment . Week 1, Site A) for Fe. The highest concentrations recorded in the Diep River were 4 mgE.-1 (water . Week 1, Site A) and 19 179 mgEkg-1 (sediment . Week 1, Site C) for Al, and 513 mgE.-1 (water . Week 27, Site A) and 106 379.5 mgEkg-1 (sediment . Week 9, Site C) for Fe. For most of the metals analysed the concentrations were higher than the recommended water quality guidelines as stipulated by the Department of Water Affairs and Forestry, the Canadian Council for the Ministers of the Environment and the accepted eworld averagef. Point sources of pollution could not be conclusively identified, but runoff from both industrial and residential areas could have contributed to the increased concentrations. Metal concentrations should be routinely monitored and the guidelines should be updated and revised based on the current state of the rivers and pollution sources