Change Detection and Notification of Webpages: A Survey <s> X-Diff Algorithm. <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> X-Diff Algorithm. <s> This paper describes Web Page Change Detection System for Selected Zone based on tree comparison mechanism corresponding to HTML pages. Two sub trees for the selected zone will be generated one for initial and another for changed version of Web Document. The Generalized Tree Comparison Algorithm is developed to compare these sub trees for selected zone. This algorithm uses the properties of HTML page and heuristics as a node of the trees. This proposed system will include functionalities and interfaces for processing user request, fetching web pages from the internet allowing users to select zone in web pages to monitor. This method performs well and is able to detect the structural as well as content level changes even at the minute level and helps to locate minor or major changes within the selected zone of document. <s> BIB002
The research carried out in [Wang et al. 2003 ] has investigated how XML documents change and to find a method to perform change detection of XML documents. The authors have pointed out the fact that XML is becoming important as it is at present the de-facto standard in publishing web applications & data transfer/transportation. "Internet Query Systems", "Search Engines", and "Continuous Query Systems" heavily rely on efficiently detecting webpage changes in XMLdocuments because of the frequent rate at which webpages change in present days. The authors have described about an algorithm named "X-Diff", which is an algorithmic model used to compute the difference in-between 2 versions of a XMLdocument. Unordered trees, structural information of XML-documents, and high performance are among the main features of "X-diff" algorithm. The authors have tested the "X-Diff" algorithm for its accuracy and efficiency of change detection by considering three main nodes in the DOM tree namely "element nodes", "text nodes" & "attribute nodes". Going beyond what has currently being done the authors have compared the ordered tree model of change detection and unordered tree model which they have used. The paper has also discussed the characteristics of XML domain and established few key concepts such as "node signature" and "XHash". 4.3.4. Other Tree Difference Algorithm. The research carried out in BIB002 , has focused on detecting changes in a specific location in a website or any document. This method involves tree comparison techniques. A majority of the existing techniques/systems check for changes in the whole webpage without allowing the user to select specific areas to monitor. When considering frequent changes, the cost of communication (or the information exchanging) will cause inefficiencies by disturbing the focus to a given context. Hence, the authors have proposed a tree comparison mechanism to overcome these difficulties. They have considered the management of zone changes (particular place in a webpage) and it is quite achievable using a tree mechanism because once a webpage is converted into XML format, it can be converted into a tree according to the HTML tags and attributes. When it has to localize the detection mechanism, focus is given only to a particular node and the detection process will continue to their child nodes. However, the authors do not mention about the depth of the tree that they are going to examine, which can be inefficient with large trees. BIB001 describes a methodology to build a model to efficiently monitor webpage changes. The authors have suggested an algorithm which efficiently identifies and extracts the changes on various versions of a particular webpage and evaluates the significance/importance of the change. This algorithmic model has 3 main sections. Initially, a document-tree is created for the webpage and then it encodes the tree and finally it matches the current version with the previous version of the encoded tree. The algorithm searches for two change types occurring in web content. They are namely, "structural changes" and "content changes". Tree models can be of two types: the 1 st type is the "ordered tree model" where "leftto-right order" between nodes is crucial and this order directly contributes to the result of change detection; the 2 nd type is "unordered tree model" where only the ancestor relationships are significant. Different studies have been carried out using these two tree models. Level Order Traversal BIB001 ] is a form of breadth first search that uses an ordered tree model. First, it constructs a document tree by taking in a HTML file and parses the elements. Then, the "opening tags" are identified as tree nodes and the tree is constructed for the webpage as illustrated in Figure 10 , while maintaining "parent-child" relationships and "left-to-right order" in between "siblings". Then the algorithm traverses through the tree to detect changes and identify at which level of the tree the changes have occurred. However, some researches [Wang et al. 2003 ] have argued that the unordered tree model can generate more accurate results.