306 CHAPTER 10 (Yahoo web hosting) INFINITE DATA PATTERN Figure
306 CHAPTER 10 INFINITE DATA PATTERN Figure 10-1. UML activity diagram for the Infinite Data pattern In Figure 10-1, a line splits the activity diagram into two pieces. The upper section is the client, or web browser. The lower section is the server side, or the HTTP server. For those not acquainted with UML activity diagrams, the starting point is the black dot in the upper-left corner, and the ending point is the black dot with a white circle around it on the right side. The first action after the starting point is a black bar indicating parallel actions. The client follows two routes because of the way that the Persistent Communications pattern is implemented using two communication streams. The route that starts with the action item Client defines stateis used to generate the structure that is sent to the server for further processing. The route that starts with the action box Query server is used to retrieve the results from the server that are then processed by the client. Let s focus our attention on the route that generates the structure that is sent to the server for further processing. The route starts with the action Client defines state that is used to transform the information on the client side into a structure. As an example, the information could be the values in an HTML form. The idea is to identify some information that when assembled as a single self-contained package represents a structure that a task on the server side operates on. The task is executed asynchronously and potentially generates some results. The next action items, State is converted into XML and XML is sent to server, represent conversion of the structure into an XML document that is sent to the server. The structure does not need to be formatted as an XML document, even though it is the preferred format. The information could be formatted by using some other text format such as XML-embedded Java- Script or JSON (http://www.json.org). As a side note, this pattern is conducive to using a format such as JSON because structured data, and not document-based data, is manipulated.
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