Integration of Heterogeneous Databases: Discovery of Meta-Information and Maintenance of Schema-Restructuring Views

In today\u27s networked world, information is widely distributed across many independent databases in heterogeneous formats. Integrating such information is a difficult task and has been adressed by several projects. However, previous integration solutions, such as the EVE-Project, have several shortcomings. Database contents and structure change frequently, and users often have incomplete information about the data content and structure of the databases they use. When information from several such insufficiently described sources is to be extracted and integrated, two problems have to be solved: How can we discover the structure and contents of and interrelationships among unknown databases, and how can we provide durable integration views over several such databases? In this dissertation, we have developed solutions for those key problems in information integration. The first part of the dissertation addresses the fact that knowledge about the interrelationships between databases is essential for any attempt at solving the information integration problem. We are presenting an algorithm called FIND2 based on the clique-finding problem in graphs and k-uniform hypergraphs to discover redundancy relationships between two relations. Furthermore, the algorithm is enhanced by heuristics that significantly reduce the search space when necessary. Extensive experimental studies on the algorithm both with and without heuristics illustrate its effectiveness on a variety of real-world data sets. The second part of the dissertation addresses the durable view problem and presents the first algorithm for incremental view maintenance in schema-restructuring views. Such views are essential for the integration of heterogeneous databases. They are typically defined in schema-restructuring query languages like SchemaSQL, which can transform schema into data and vice versa, making traditional view maintenance based on differential queries impossible. Based on an existing algebra for SchemaSQL, we present an update propagation algorithm that propagates updates along the query algebra tree and prove its correctness. We also propose optimizations on our algorithm and present experimental results showing its benefits over view recomputation

Discovery of High-Dimensional Inclusion Dependencies

Determining relationships such as functional or inclusion dependencies within and across databases is important for many applications in information integration. When such information is not available as explicit meta data, it is possible to discover potential dependencies from the source database extents. However, the complexity of such discovery problems is typically exponential in the number of attributes. We have developed an algorithm for the discovery of inclusion dependencies across high-dimensional relations in the order of 100 attributes. This algorithm is the first to efficiently solve the inclusion-dependency discovery problem. This is achieved by mapping it into a progressive series of clique-finding problems in k-uniform hypergraphs and solving those. Extensive experimental studies confirm the algorithm 's efficiency on a variety of real-world data sets

Integrating the Rewriting and Ranking Phases of View Synchronization

Materialized views (data warehouses) are becoming increasingly important in the context of distributed modern environments such as the World Wide Web. Information sources (ISs) in such an environment may change their capabilities (schema). This causes a data warehouse defined by view queries over distributed sources to become undefined. Algorithms have been proposed to evolve (rewrite) view queries after capability changes of ISs by exploiting meta-descriptions about ISs and their relationships. This view rewriting process is referred to as view synchronization. View synchronization algorithms generate a potentially large number of valid solutions for the rewriting of a view query. Our analysis, as presented in this paper, shows that the most expressive algorithm for view synchronization has very high complexity (in O(n!)). The objective of this current work is hence to propose optimizations for this view synchronization process in order to make it practically usable. For this, we iden..

Maintaining Data Warehouses Over Changing Information Sources

This article characterizes the types of dynamicity (such as data updates, schema changes, and constraint modifications) as well as their explicit and implicit generation. This article also identifies issues for data warehousing systems that occur when the possibility of information source changes is taken into consideration. Such issues include adapting wrappers to information source changes, adapting view definitions to changes, or adapting the data content (extent) of the data warehouse. Lastly, possible candidate solutions for some of these problems, especially as explored in the context of the Evolvable View Environment (EVE) system, are outlined. Such flexible data warehousing technology will allow more users to make use of distributed information over networks and increase the productivity of users and system administrators by maintaining customized interfaces to information that can be automatically maintained even under changes of the underlying system

The effect of age on optic nerve head blood flow. Investigative Ophthalmology and Visual Sience 46(4

PURPOSE. To examine whether optic nerve head blood flow changes with aging. METHODS. One randomly chosen eye of each of 103 healthy subjects (age range, 22-76 years) was examined by laser Doppler flowmetry. Relative capillary blood flow, velocity, and volume of the moving red blood cells were measured at the temporal and nasal neuroretinal rim of the optic nerve head. For statistical analysis, linear regression analysis and partial correlations were calculated. RESULTS. Velocity increased with age. The Pearson correlation coefficient (R) between age and velocity was 0.49 temporally and 0.56 nasally. The correlation was significantly different from 0 (both P Ͻ 0.0005). Volume decreased with increasing age. The Pearson correlation coefficient between age and volume was Ϫ0.47 temporally and Ϫ0.40 nasally. The correlation was significantly different from 0 (both P Ͻ 0.0005). Flow decreased with increasing age. The Pearson correlation coefficient between age and flow was Ϫ0.27 temporally and Ϫ0.31 nasally. The correlations were significantly different from 0 (P ϭ 0.006 and P ϭ 0.002, respectively). Partial correlation coefficients between the perfusion parameters and age, after correcting for systolic and diastolic blood pressure, heart rate, gender, and IOP, were similar compared to the Pearson correlation coefficients and remained statistically significant. CONCLUSIONS. The perfusion of the optic nerve head is altered with increasing age. The results suggest that the blood supply is reduced in elderly subjects. (Invest Ophthalmol Vis Sci. 2005;46:1291-1295) DOI:10.1167/iovs.04-0987 I n the process of aging, various organ systems are affected in the human body. With regard to the optic nerve head, histologic alterations have been described suggesting a vascular impairment with increasing age. 1 As vascular risk factors (e.g., reduced perfusion of the optic nerve head [ONH]) may play a role in the pathogenesis of glaucoma 2-4 and as glaucoma is more common in elderly than in younger individuals, it seems important to know how the perfusion of the ONH is affected by increasing age. In vivo studies examining retrobulbar vessels, retinal, and choroidal perfusion showed a decrease of ocular perfusion with increasing age. SUBJECTS AND METHODS Subjects In a cross-sectional study, one randomly chosen eye of 103 healthy volunteers of different ages was examined. The subjects were recruited from persons accompanying patients and from staff, their friends, and their families. All subjects received an ophthalmic clinical examination, including evaluation of the optic disc showing no signs of glaucoma. Optic discs were considered normal if they had intact rims and no hemorrhages, notches, excavation, nerve fiber layer defects, or asymmetry of the vertical cup-to-disc ratio Ͼ0.2. None of the subjects had a history of increased intraocular pressure Ͼ21 mm Hg or was using topical medication. Subjects did not have cardiovascular disease and were not taking any systemic medication that might affect the vascular system (e.g., ␤-blockers, or calcium channel antagonists). In keeping with the tenets of the Declaration of Helsinki, written documentation of informed consent was taken and the study was explained to the subjects. The research was approved by the local ethics committee. The age of the subjects ranged between 22 and 76 years (mean age, 42.5 Ϯ15.0). Sixty-six subjects were women and 37 were men. Methods The laser Doppler flowmeter (LDF; model 4000; Oculix Sarl, Arbaz, Switzerland) according to Riva was used for the blood flow measurements. The technical details of the instrument have been described in detail elsewhere. 9 Briefly, this technique is based on the optic Doppler effect. Emitted laser light with a frequency of 670 nm is focused on the surface of the optic nerve head. The measured area has a diameter of approximately 160 m. The coherent light is scattered by the moving red blood cells (RBCs) and the stationary tissue. The scattering caused by the RBCs leads to a frequency shift of the laser light. The scattering caused by the stationary tissue leads only to a randomization of the light directions striking the RBCs. The broadened spectrum of scattered laser light is subjected to spectral analysis. From this analysis the parameters velocity and volume are obtained. The parameter velocity represents the speed of the moving RBCs and the parameter volume corresponds to the amount of the moving RBCs. From these two parameters, the parameter flow is calculated representing the blood flow of the moving RBCs. These parameters represent relative, not absolute, values. Volume and flow are measured in arbitrary units [AU] and velocity in kilohertz. Before the examination, the pupil was dilated with 1 drop of tropicamide 1%. The measurements were performed in a darkened room. Measurements were taken at the nasal and temporal neuroretinal rim of the optic nerve head, away from visible vessels. For each measurement, during a period of several seconds, continuous recordings of the three parameters flow, volume, and velocity were obtained. As the recordings can be disturbed by events such as lid movements and head motion, a masked observer selected the part of the recording that showed a stable circulatory parameter. These parts of the measurements were used for the analysis. Immediately after the flowmeter measurement, intraocular pressure was taken by applanation tonometry, and systemic perfusion parameters such as systolic and diastolic brachial arterial blood pressure and the heart rate were measured

Data Warehouse Evolution: Trade-offs between Quality and Cost of Query Rewritings

The problem of rewriting queries has been heavily explored in recent years, including in work on query processing and optimization, semantic query refinement in decentralized environments, the rewriting of queries using views, and view maintenance. Previous work has made the restricting assumption that the rewritten query must be equivalent to the initially given query. We now propose to relax this assumption to allow for query rewriting in situations where equivalent rewritings may not exist -- yet alternate not necessarily equivalent query rewritings may still be preferable to users over not receiving any answers at all. Our approach is based on a preference model, an extension of SQL called E-SQL, that captures the intention of the query by how much deviation from the original query would still be acceptable to the user. In this paper, we introduce an analytical model of query rewritings that incorporates measures of quality of a query in addition to the commonly studied measures of..

Data warehouse evolution: trade-offs between quality and cost of query rewritings

The desirability of a query rewriting is influenced by quality and cost. To assess rewritings on both factors, the Quality-Cost Model (QC Model) has been developed. Since data content changes are more frequent than scheme changes at the ISs, the long-term (incremental) view maintenance cost has been used as an indicator for costs. Finally, the quality factor is then combined with the cost factor to decide the overall ranking of a rewriting

Non-Equivalent Query Rewritings

Previous work in query rewriting has made the restricting assumption that the rewritten query must be equivalent to the initially given query. We now propose to relax this assumption to allow for query rewriting in situations where equivalent rewritings may not exist -- yet alternate not necessarily equivalent query rewritings may still be preferable to users over not receiving any answers at all. In this paper, we apply this concept of non-equivalent query rewriting to the problem of maintaining view definitions (data warehouses), now allowing us to handle not only data but also schema-level changes of the underlying information sources. This relaxed query notion however raises the new issue of the evaluation of such queries. For this purpose, we introduce an analytical model of query rewritings that incorporates measures of information preservation (quality) of a query in addition to the commonly studied measures of view maintenance performance (query cost). Both quality and cost ar..

Feed Intake Patterns and Immediate Glycaemic and Insulinaemic Responses of Horses Following Ingestion of Different Quantities of Starch From Oat, Barley and Grains

BACKGROUND: Relevant literature indicate that more than 0.8 g starch/kg body weight from compounded feed composed of different starch sources induces disproportionate glycaemic and insulinaemic responses in horses. OBJECTIVE: It should be investigated whether crushed oats, barley and maize also cause a disproportionate increase in plasma glucose and insulin when fed as the only concentrate in quantities equal to and above 0.8 g starch/kg body weight. METHOD: Four mares received hay plus oats, barley and maize, respectively, in quantities equal to 0.8, 1.0 and 2.0 g starch/kg body weight. At the test days, chewing parameters were detected and blood sampled before and 30, 60, 90 and 120 min after the concentrate meal. Plasma glucose and insulin were measured and areas under the curve were calculated. RESULTS: Maize was ingested particularly slowly (dry matter basis; P < 0.05), but glycaemic and insulinaemic responses were particularly low (starch basis; P < 0.05). In general, the glycaemic responses were highest with 1 g starch/kg body weight (P < 0.05). The quantity of starch had no effect on the insulinaemic response (P > 0.05). A defined increase in plasma glucose induced the highest insulinaemic response with oat grains. CONCLUSION: Oats and barley are ingested faster and induce higher glycaemic and insulinaemic responses than maize. Until 120 min postprandial, elevated quantities of starch from these grains seem to induce no disproportionate or at least linear increase of plasma glucose and insulin. The insulinaemic response to a defined increase of plasma glucose is particularly pronounced with oats