Roger Weber

Active XML: peer-to-peer data and web services integration

Publisher Summary The content of an Active eXtensible Markup Language (AXML) document is dynamic, because it is possible to specify when a service call should be activated (for example, when needed, every hour, etc.), and for how long its result should be considered valid. Thus, this simple mechanism allows capturing and combining different styles of data integration, such as warehousing and mediation. To fully take advantage of the use of services, AXML also allows calling continuous services (that provide streams of answers) and services supporting intentional data (AXML document including service calls) as parameters and/or result. The latter feature leads to powerful, recursive integration schemes. The AXML framework is centered on AXML documents , which are XML documents that may contain calls to Web services. When calls included in an AXML document are fired, the latter is enriched by the corresponding results.

Trading Quality for Time with Nearest Neighbor Search

In many situations, users would readily accept an approximate query result if evaluation of the query becomes faster. In this article, we investigate approximate evaluation techniques based on the VA-File for Nearest-Neighbor Search (NN-Search). The VA-File contains approximations of feature points. These approximations frequently suffice to eliminate the vast majority of points in a first phase. Then, a second phase identifies the NN by computing exact distances of all remaining points. To develop approximate query-evaluation techniques, we proceed in two steps: first, we derive an analytic model for VA-File based NN-search. This is to investigate the relationship between approximation granularity, effectiveness of the filtering step and search performance. In more detail, we develop formulae for the distribution of the error of the bounds and the duration of the different phases of query evaluation. Based on these results, we develop different approximate query evaluation techniques. The first one adapts the bounds to have a more rigid filtering, the second one skips computation of the exact distances. Experiments show that these techniques have the desired effect: for instance, when allowing for a small but specific reduction of result quality, we observed a speedup of 7 in 50-NN search.

Scalable peer-to-peer process management - the OSIRIS approach

The functionality of applications is increasingly being made available by services. General concepts and standards like SOAP, WSDL, and UDDI support the discovery and invocation of single Web services. State-of-the-art process management is conceptually based on a centralized process manager. The resources of this coordinator limit the number of concurrent process executions, especially since the coordinator has to persistently store each state change for recovery purposes. In this paper, we overcome this limitation by executing processes in a peer-to-peer way exploiting all nodes of the system. By distributing the execution and navigation costs, we can achieve a higher degree of scalability allowing for a much larger throughput of processes compared to centralized solutions. This paper describes our prototype system OSIRIS, which implements such a true peer-to-peer process execution. We further present very promising results verifying the advantages over centralized process management in terms of scalability.

Active XML: A Data-Centric Perspective on Web Services

We propose in this chapter a peer-to-peer architecture that allows for the integration of distributed data and Web services. It relies on a language, Active XML, where documents embed calls to Web services that are used to enrich them, and new Web services may be defined by XQuery queries on such active documents. Embedding calls to functions or even to Web services inside data is not a new idea. Our contribution, however, is to turn them into a powerful tool for data and services integration. In particular, the language includes linguistic features to control the timing of service call activations. Various scenarios are captured, such as mediation, data warehousing and distributed computation. A first prototype is also described.

Postischemic Blood Flow Response in Hypercholesterolemic Patients

We undertook this cross-sectional study to compare the mechanical behavior and postischemic response of the radial artery of 15 newly diagnosed hypercholesterolemic patients with those of 15 age- and sex-matched normocholesterolemic control subjects and 21 hypercholesterolemic patients treated for 2 years with an 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (simvastatin, 10 to 20 mg/d). At the time of the study total cholesterol levels were at 7.9 +/- 0.2, 4.9 +/- 0.2, and 6.0 +/- 0.3 mmol/L in the three groups, respectively (mean +/- SEM, P < .001). High-resolution, noninvasive echotracking for assessment of internal arterial diameter was combined with measurements of blood flow velocity by Doppler and blood pressure by photoplethysmography. Radial cross-sectional compliance and distensibility were similar in all groups. Forearm blood flow and flow-mediated dilation were measured after a 5-minute upper arm occlusion. Flow was calculated from the vessel diameter and blood flow velocity recorded simultaneously at the same site. Flow-mediated dilation after ischemia was not significantly different among the three groups. However, forearm blood flow increase was markedly blunted (P < .01) in untreated hypercholesterolemic patients (211%) compared with the normocholesterolemic control subjects (411%) and treated patients (365%). These findings suggest that the distensibility of the radial artery, a muscular conduit vessel usually devoid of atherosclerotic lesions, and its flow-mediated dilation are preserved in hypercholesterolemic patients. In contrast, forearm resistance vessels exhibit a markedly reduced postischemic blood flow response that may be restored by prolonged lipid-lowering intervention.

Contributions of Vascular Tone and Structure to Elastic Properties of a Medium-Sized Artery

Isobaric compliance and distensibility of the radial artery were recently reported to be normal or slightly increased in untreated hypertensive patients. However, these findings provide no information on the intrinsic mechanical properties of the wall material. To address this question, we determined intima-media wall thickness, wall-to-lumen ratio, and incremental elastic modulus in the radial artery of 25 untreated hypertensive patients with blood pressure of 150 +/- 14/103 +/- 6 mm Hg (mean +/- SD) and 25 matched control subjects with blood pressure of 118 +/- 9/79 +/- 6 mm Hg. High-resolution echotracking for assessment of internal diameter and intima-media wall thickness was combined with measurements of blood flow velocity by Doppler and blood pressure by photoplethysmography. In addition, isobaric compliance and distensibility and incremental elastic modulus were measured at peak diameter during reactive hyperemia after a 5-minute brachial occlusion. No significant difference was found between the two groups for isobaric compliance or distensibility at baseline or during hyperemia. However, incremental elastic modulus at 100 mg Hg tended to be lower in hypertensive patients than control subjects (1.9 +/- 1.1 versus 2.5 +/- 1.2 mm Hg x 10(4), P = .1) in resting conditions. Hypertensive patients and control subjects had similar internal diameters (2.47 +/- 0.32 versus 2.41 +/- 0.35 microm), but intima-media wall thickness and wall-to-lumen ratio were significantly increased in hypertensive patients compared with control subjects (0.268 +/- 0.032 versus 0.236 +/- 0.025 mm -P < or = .01- and 0.220 +/- 0.038 versus 0.195 +/- 0.028 -P < or = .05-, respectively). Peak hyperemic blood flow response (hypertensive patients versus control subjects: 349% versus 360% increase from baseline) and reactive hyperemic dilation (7.2% versus 7.9%) were similar in amplitude and duration in the two groups. These results suggest that wall thickening is an adaptive process that reduces wall tension in hypertensive patients while preserving a normal mechanical behavior of the radial artery. This is most likely accomplished by modification of the incremental elastic modulus of wall components rather than by a change in vascular tone.

Multiresolution compression and reconstruction

The paper presents a framework for multiresolution compression and geometric reconstruction of arbitrarily dimensioned data designed for distributed applications. Although being restricted to uniform sampled data, the versatile approach enables the handling of a large variety of real world elements. Examples include nonparametric, parametric and implicit lines, surfaces or volumes, all of which are common to large scale data sets. The framework is based on two fundamental steps: compression is carried out by a remote server and generates a bit-stream transmitted over the underlying network. Geometric reconstruction is performed by the local client and renders a piecewise linear approximation of the data. More precisely, the compression scheme consists of a newly developed pipeline starting from an initial B-spline wavelet precoding. The fundamental properties of wavelets allow progressive transmission and interactive control of the compression gain by means of global and local oracles. In particular the authors discuss the problem of oracles in semiorthogonal settings and propose sophisticated oracles to remove unimportant coefficients. In addition, geometric constraints such as boundary lines can be compressed in a lossless manner and are incorporated into the resulting bit-stream. The reconstruction pipeline performs a piecewise adaptive linear approximation of data using a fast and easy to use point removal strategy which works with any subsequent triangulation technique.

Efficient region-based image retrieval

Region-based image retrieval(RBIR) was recently proposed as an extension of content-based image retrieval(CBIR). An RBIR system automatically segments images into a variable number of regions, and extracts for each region a set of features. Then, a dissimilarity function determines the distance between a database image and a set of reference regions. Unfortunately, the large evaluation costs of the dissimilarity function are restricting RBIR to relatively small databases. In this paper, we apply a multi-step approach to enable region-based techniques for large image collections. We provide cheap lower and upper bounding distance functions for a recently proposed dissimilarity measure. As our experiments show, these bounding functions are so tight, that we have to evaluate the expensive distance function for less than 0.5\%of the images. For a typical image database with more than 370,000images, our multi-step approach improved retrieval performance by a factor of more than5 compared to the currently fastest methods.

PEER-TO-PEER EXECUTION OF (TRANSACTIONAL) PROCESSES

Standards like SOAP, WSDL, and UDDI facilitate the proliferation of services. Based on these technologies, processes are a means to combine services to applications and to provide new value-added s...

Web service composition with O'GRAPE and OSIRIS

Services are well known building blocks in modern in-formation systems. Technologies and standards likeXML, SOAP (Simple Object Access Protocol) [8], andWSDL (Web Service Description Language) [10] pro-vide a simple means to describe these services and tomake them accessible to a large community in a dis-tributed environment. Yet, the full potential of webservices becomes only apparent if we can combine sev-eral service invocations in a well-defined order andwith well-designed execution guarantees to establisheven more powerful composite services. Among oth-ers, processes provide a simple mechanism to composeservices [1]. A process defines the logical dependenciesbetween independent services by specifying an invoca-tion order (control flow) as well as rules for the trans-fer of data items between different invocations (dataflow). In addition and following the model of trans-actional processes [7], we can define the transactionalbehavior and execution guarantees to ensure a correctexecution of processes in case of concurrency and fail-ures. An infrastructure for transactional processes hasto support all these run-time features. Furthermore,a graphical process modeling tool should support thespecification of all these features. An important aspectis that such a modeling tool is transparently integratedinto the process management environment.In addition to the transactional semantics of ser-vice composition, several other run-time aspects arecrucial. Usually, several semantically equivalent webservices are available at different places. An infrastruc-ture for process execution should equally distribute theload over all web service providers. Similarly, processexecutions should take costs and expected executiontimes into account to optimize response times. To this