Refining Statistical Data on the Web

The Web has grown into a heterogeneous open data space of interlinked documents, tables, and databases. Open datasets on the Web are often used as input for many knowledge discovery processes, which aim at finding patterns within those data. However, open datasets on the Web are hardly ever ready for analysis, and require careful data preparation. Even though current efforts focus on making analysis more efficient, empirical studies show that data preparation takes 60% of the total time spent. Statistical data are data subject to analysis by statistical methods and tools. A number of problems in these statistical datasets severely hamper their preparation. First, non-standard legacy formats have a decaying support over time that negatively affects accessibility of these data. Second, data errors, typos and other flaws are hard to detect and correct, and affect how meaningful results are in analysis. Third, data curation procedures are often hard-coded in implementations or hidden in closed-source systems, obstructing their reusability. Moreover, if these datasets contain also a historical dimension, two additional problems occur. First, operational sources of historical statistics have often been lost over time, leaving partial analytical views as the only representation preserved in archives. Second, time series are usually poorly harmonized, due to the incompatibility of changing classification systems. Data scientists try to resolve all these data preparation issues by resort to painful data munging, which results in the aforementioned time spent. In this thesis, solutions to these problems that take advantage of Semantic Web technologies are proposed. Multiple statistical datasets in the domain of Social and Economic History, where this kind of data is prototypical, are used as a case study. Therefore, the main research question addressed in the thesis is: How can Semantic Web technologies contribute to solve integration problems of legacy statistical collections, lower their access costs, measure the quality of their diachronic schemas and their constrained instances, and facilitate their transformation in a standards-compliant and implementation-independent way