Change Detection and Notification of Webpages: A Survey <s> Customized Architectures <s> An end block adapted for use on a kiln car includes a refractory body having a transverse projection at a front end and a transverse recess at a rear end. The recess is dimensioned to receive therewithin a projection on the front end of another block with a loose fit therebetween. A sealing layer of resilient refractory material may be disposed within the recess for contact with the front end projection of another block. <s> BIB001 </s> Change Detection and Notification of Webpages: A Survey <s> Customized Architectures <s> Search engines use crawlers to traverse the Web in order to download web ::: pages and build their indexes. Maintaining these indexes up-to-date is an ::: essential task to ensure the quality of search results. However, changes in ::: web pages are unpredictable. Identifying the moment when a web page changes ::: as soon as possible and with minimal computational cost is a major challenge. ::: In this article we present the Web Change Detection system that, in a best ::: case scenario, is capable to detect, almost in real time, when a web page ::: changes. In a worst case scenario, it will require, on average, 12 minutes to ::: detect a change on a low PageRank web site and about one minute on a web site ::: with high PageRank. Meanwhile, current search engines require more than a ::: day, on average, to detect a modification in a web page (in both cases). <s> BIB002 </s> Change Detection and Notification of Webpages: A Survey <s> Customized Architectures <s> Web pages at present have become dynamic and frequently changing, compared to the past where web pages contained static content which did not change often. People have the need to keep track of web pages which are of interest to them, using bookmarks in the web browser and continuously keep track of them in order to get the updates. Tracking changes which occur in these bookmarked web pages and getting updates has become a significant challenge in the current context. Hence there is a need for better and convenient methods to keep track of web pages. Many researches and implementations have been carried out in order to increase the efficiency of change detection of web pages and related algorithms. In this paper, we discuss the architectural aspects of change detection systems and introduce an optimized change detection solution including a web service, browser plugin and an email notification service. Consequently, this research will pave the way for a novel research area to explore. <s> BIB003 </s> Change Detection and Notification of Webpages: A Survey <s> Customized Architectures <s> Digital documents are likely to have problems associated with the persistence of links, especially when dealing with references to external resources. People keep track of various webpages of their interest using distributed digital collections and without possession of these documents; the curator cannot control how they change. In the current context, managing these distributed digital collections and getting notifications about various changes have become a significant challenge. In this paper, we address the architectural aspects of change detection systems and present optimized change detection architecture, including a web service and a browser plugin, along with an email notification service. We have performed an experimental study on our hybrid architecture for change detection in a distributed digital collection. The proposed method introduces a preliminary framework that can serve as a useful tool to mitigate the impact of unexpected change in documents stored in decentralized collections in the future. <s> BIB004
Several customized architectures can be found in which researchers have tried to improve the efficiency from an architectural perspective. A design to crawl webpages in parallel using several machines and integrate the problems with crawling has been proposed in BIB001 . They have designed a new architecture to build a parallel crawler. The proposed architecture consists of two main components. They are the "Multi-threaded Server (MT-Server)" and the "client crawlers." "MT-Server" is the principal component that manages a collection of client machine connections, which downloads and crawls webpages. It has a special methodology to distribute URLs among the clients when their "priority index" is determined. The client crawlers are considered as the different machines which interact with the server. The client count that can be supported may vary according to the available resources and their implementation. Furthermore, there exists no communication between clients and the clients interact only with the server. However, scaling the system can result in high costs as the server node count has to grow. Work carried out in BIB002 presents a system with a collaborative architecture to detect changes in distributed systems. The authors have proposed a "Web Change Detection (WCD) system". The four major components of this system's architecture are the "web client", "web server", "WCD agent" and "WCD server". "Web client" is a general browser of the web, which loads the webpages. "Web server" is a general-server that caches the webpages that were monitored. "WCD agent" is an application operating in the browser that sends information about modifications that have occurred in webpages to the "WCD server". "WCD server" stores and sends the "WCD agents" to clients and stores the data about monitored webpages. In order to detect the near duplicates, "PageRank" [30] values have been considered along with the "shash tool" [Shash Tool 2015] . High change detection rates and a low cost of maintenance have been produced by this tool. However, in times of excessive usage, if the system gets many requests, it may fail to process them in real-time. Figure 6 illustrates the architecture of the "WCD system", including its main components. An "approach for distributed aggregation, faster scalable content classification and change detection in web content" has been proposed in  ]. The authors have presented an algorithm to determine webpage changes and a method to identify what field has been altered with the help of a data structure named "bloom filters"  ]. Web crawlers are being used to collect details about pages and URLs. It uses Bloom filters to identify the duplicate URLs in a webpage. Hash keys for every visited URL are saved in the bloom filter. Bloom filter entries will be validated when new URLs are discovered. This prevents the crawling mechanism from repeating in loops. The system creates a hash key for the content that has been crawled and checks the presence of the hash within the bloom lookup. If present, the content is same as the existing content; otherwise the content has been updated. If the hash key for the URL is not found, then the URL is added to the bloom filter lookup file and a hash for the crawled content is created and inserted. This method increases the efficiency of the crawling process as it distributes the workload. Furthermore, the strong association of crawlers to working machines will be minimized and the crawlers will be able to function without any restrictions in distributed networks. A hybrid architecture for CDN is proposed in BIB003 ] BIB004 ]. This architecture is a hybrid of server-based and clientbased architectures. It has two independent crawling schedules for the server and for the clients. The server will crawl all the webpages it has registered, and the clients will crawl the webpages which they want to track. The change detection process occurs independently in the server and clients. If the server detects a change, it will be notified to the clients who are interested. If a change is detected by a client, then it will directly report back to the server and the server will notify the clients who are interested. According to this architecture considered, the time elapsed in between two consecutive server poll actions is divided among the available clients which in turn speeds up the detection process. Table I presents a summary of the various architectures that are being used by commercially available CDN systems and that have been proposed by researchers. 