TAILIEUCHUNG - Oracle XSQL- P5

Oracle XSQL- P5Welcome to the exciting world of eXtended Structured Query Language (XSQL) development! What’s so exciting? Efficiency and ease of use. XSQL isn’t some razzle-dazzle technology to wow your users. It also isn’t the latest X standard du jour that no one can stop talking about until you ask, “But what does it do for me today?” The problem with all of the great stuff out there is that no one technology does it all. | 60 Chapter 4 Database .xsl .xsql Figure XSQL programmatic invocation architecture. XSQL Servlet XSQL servlet invokes the XSQL page processor. You will have a lot of interaction with the XSQL servlet. As described in the previous chapter you must register the XSQL servlet with the servlet engine. There are also two servlet-specific configuration elements output-buffer-size and suppress-mime-types. Though XSQL servlet is the Web interface to all XSQL functionality it itself does little. It receives a request and passes it to the XSQL page processor. The XSQL page processor does the heavy lifting and hands back a result. If you have buffering turned on the XSQL servlet will buffer the output for you. If the XSQL servlet is configured appropriately it will suppress the sending of character-encoding information. And that s about it. It s time to move on to the real player the XSQL page processor XSQL Page Processor The XSQL page processor as the name applies is responsible for processing the XSQL pages. It is the magician of the system. It takes a simple XSQL and a XSLT file connects XSQL Architecture 61 to the database and gives you back something presentable. At the highest level it performs this function as described in Figure . This invoker is the XSQL servlet the XSQL command line or the XSQL request. At the time of invocation it is possible to know how the XSQL page processor was invoked. For this discussion you ll learn how the XSQL page processor behaves regardless of how it is invoked. The XSQL page processor is already loaded into memory at the time of invocation except when you call it from the command line or make the first call for the instance of the JVM. When the XSQL page processor loads it reads its file. At about a 5 000-ft level the XSQL page processor does the following when invoked 1. Parses the request from the invoker 2. Selects the XSQL page 3. Processes the actions described in the XSQL page most of the time by going to the

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