P. P. S. Narayan

Optimizing view queries in ROLEX to support navigable result trees

An increasing number of applications use XML data published from relational databases. For speed and convenience, such applications routinely cache this XML data locally and access it through standard navigational interfaces such as DOM, sacrificing the consistency and integrity guarantees provided by a DBMS for speed. The ROLEX system is being built to extend the capabilities of relational database systems to deliver fast, consistent and navigable XML views of relational data to an application via a virtual DOM interface. This interface translates navigation operations on a DOM tree into execution-plan actions, allowing a spectrum of possibilities for lazy materialization. The ROLEX query optimizer uses a characterization of the navigation behavior of an application, and optimizes view queries to minimize the expected cost of that navigation. This paper presents the architecture of ROLEX, including its model of query execution and the query optimizer. We demonstrate with a performance study the advantages of the ROLEX approach and the importance of optimizing query execution for navigation.

Composing XSL transformations with XML publishing views

While the XML Stylesheet Language for Transformations (XSLT) was not designed as a query language, it is well-suited for many query-like operations on XML documents including selecting and restructuring data. Further, it actively fulfills the role of an XML query language in modern applications and is widely supported by application platform software. However, the use of database techniques to optimize and execute XSLT has only recently received attention in the research community. In this paper, we focus on the case where XSL transformations are to be run on XML documents defined as views of relational databases. For a subset of XSLT, we present an algorithm to compose a transformation with an XML view, eliminating the need for the XSLT execution. We then describe how to extend this algorithm to handle several additional features of XSLT, including a proposed approach for handling recursion.

VoIP service quality monitoring using active and passive probes

Service providers and enterprises all over the world are rapidly deploying Voice over IP (VoIP) networks because of reduced capital and operational expenditure, and easy creation of new services. Voice traffic has stringement requirements on the quality of service, like strict delay and loss requirements, and 99.999% network availability. However, IP networks have not been designed to easily meet the above requirements. Thus, service providers need service quality management tools that can proactively detect and mitigate service quality degradation of VoIP traffic. In this paper, we present active and passive probes that enable service providers to detect service impairments. We use the probes to compute the network parameters (delay, loss and jitter) that can be used to compute the call quality as a Mean Opinion Score using a voice quality metric, E-model. These tools can be used by service providers and enterprises to identify network impairments that cause service quality degradation and take corrective measures in real time so that the impact on the degradation perceived by end-users is minimal

ROLEX: relational on-line exchange with XML

1. OVERVIEW ROLEX is a research system for closely coupled XML-relational interoperation [2]. Whereas typical XML-based applications interoperate with existing relational databases via a “shred-and-publish” approach, the ROLEX system seeks to provide direct access to relational data via XML interfaces at the speed of cached XML data. To achieve this, ROLEX is integrated tightly with both the DBMS and the application through a standard interface supported by most XML parsers, the Document Object Model (DOM). Thus, in general, an application need not be modified to be used with ROLEX. With the DBMS providing performance qualitatively similar to cached data, XML applications can rely on it for concurrency control and recovery services. To support our integration model and performance goals, ROLEX is built on the DataBlitz Main-Memory Database System, allowing us to capitalize on low-latency access to data while still providing concurrency control and recovery [1]. The DOM interface supports the expected navigation functions: parent-to-child, child-to-parent, and sibling-to-sibling. A DOM interface to an XML view query supports all the DOM operations and behaves as if the user were navigating the XML document resulting from the query. In ROLEX, we implement a virtual DOM tree that goes a step further by providing the same interface without creating a physical DOM tree. A novelty of ROLEX is that it uses a navigational profile for the user or application when it optimizes view-query plans. While navigational profiles can, in principle, be quite complex, we currently adopt a very simple model. If n is a node in the schema tree with parent p, the navigation profile stores the probability that some node in the DOM tree generated by n will be visited given that its parent, generated by p, has been visited. Query output is produced by a navigable query plan. It provides, for each node n in the schema tree of a view query, two entities: (1) a subplan for evaluating the tag query for n, and (2) a navigation index. The navigation index serves to materialize the output of the tag query and supports efficient lookup based on parameter values,