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Technical Reports Authored or Co-Authored by Prof. Nick Roussoupoulos
Papers resulting from CSHCN-related research are periodically added to the Institute for Systems Research Technical Report Database where they can be browsed by year or searched by author or keywords.
Update Propagation Strategies for Improving the Quality of Data on the Web (CSHCN TR 2001-15) by Alexandros Labrinidis, Nick Roussopoulos
Dynamically generated web pages are ubiquitous today but their high demand for resources creates a huge scalability problem at the servers. Traditional web caching is not able to solve this problem since it cannot provide any guarantees as to the freshness of the cached data. A robust solution to the problem is web materialization, where pages are cached at the web server and constantly updated in the background, resulting in fresh data accesses on cache hits. In this work, we define Quality of Data metrics to evaluate how fresh the data served to the users is. We then focus on the update scheduling problem: given a set of views that are materialized, find the best order to refresh them, in the presence of continuous updates, so that the overall Quality of Data (QoD) is maximized. We present a QoD-aware Update Scheduling algorithm that is adaptive and tolerant to surges in the incoming update stream. We performed extensive experiments using real traces and synthetic ones, which show that our algorithm consistently outperforms FIFO scheduling by up to two orders of magnitude.
Adaptive WebView Materialization (CSHCN TR 2001-14) by Alexandros Labrinidis, Nick Roussopoulos
Dynamic content generation poses huge resource demands on web servers, creating a scalability problem. WebView Materialization, where web pages are cached and constantly refreshed in the background, has been shown to ameliorate the scalability problem without sacrificing data freshness. In this work we present an adaptive online algorithm to select which WebViews to materialize, that realizes the trade-off between Quality of Service and Quality of Data. Our algorithm performs very close to the static, off-line optimal algorithm, and, under rapid workload changes, it outperforms the optimal.
WebView Materialization (CSHCN TR 2000-4) by Alexandros Labrinidis, Nicholas Roussopoulos
A WebView is a web page automatically created from base data typically stored in a DBMS. Given the multi-tiered architecture behind database-backed web servers, we have the option of materializing a WebView inside the DBMS, at the web server, or not at all, always computing it on the fly (virtual). Since WebViews must be up to date, materialized WebViews are immediately refreshed with every update on the base data.
In this paper we compare the three materialization policies (materialized inside the DBMS, materialized at the web server and virtual) analytically, through a detailed cost model, and quantitatively, through extensive experiments on an implemented system. Our results indicate that materializing at the web server is a more scalable solution and can facilitate an order of magnitude more users than the virtual and materialized inside the DBMS policies, even under high update workloads.
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