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Posted 10 Sep 2006

XML-new mainland of report datasource

, 27 Jul 2007
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How to get report data from XML document.


This article introcuce a universal way to get data from XML document for report.

( Chinese version: )
With the developing of B/S system and XML technology popularization , more and more data package into XML to save and throw out .Those data mostly come from database , and worked , it is more reduce and more close to application . If report tool and use those XML data , it can reduce query on database and compute data , because the creater of XML data has done thos work . So I say XML is a new mainland of report datasource .

Old report tools mostly only can read data from RDBMS , it can not handl other kind data . but with the developing of the time , some tools append ability to handle XML document , but developer need programing , create and config extend-ware , so the report system is complex and with nimiety interface , developer need observe many stand , it there are many XML format , developer have to create many kind of extend-ware , the work is large .

It people realization a kind of universal method to handle XML document , collect report data from all kind of XML document .you can define some report template , and tell report engine than how to read data from XML document , then you need not develop extend-ware to handld all of or mostly of XML document , this can reduce work .

Then how to universal handle XML document which complicated and like a tree ?

We know , there are two style to handle XML document , one is DOM style , the other is SAX sytle . DOM style is convenient , but it is slow and need many memory , SAX style is fast , need not many memory , but is not convenient . In .NET framework , use object System.Xml.XmlDocument to realization DOM style , use XmlReader to realization SAX style .

W3C organize design XML for save and exchange a few of data convenient , not think over redundance . So if there are exist huge XML document in one system , mostly it think that use XML technology out of the way . I think the report tool is need not handle large big XML document , so for expedient realization , I use DOM style to handle XML document .

In .NET framework , use a XmlDocument object load a XML document , and you can get a XML DOM tree which it's root is XmlDocument , to a XML DOM tree , it is natural to use XPath technology to read data from XML DOM tree . XPath is a language for addressing partys of an XML document .

Old report datasource model is two layers , first layer is datasource , the 2th is field . So in the abstract , it can handle XML document once time , just from root element of XML document , use XPath to get field value . and after once time read , the XML document can not use again . but in many time , It need read more data from XML document , then the old two-layers report datasource model is not enough .

For read more data from XML document , I think out a multi-layer datasource model , in this model , datasource structure can view as a tree , each node of datasource tree can mapping a node in XML dom tree use an XPath express . the children of a datasource node can mapping an xml node in the same way . So in this way , after cycle and recursion , multi-layer datasource structure can mapping an XML dom tree unlimited . multi-layer datasource model is a tree , XML DOM is a tree too , so the mapping work is bind tow tree together , and XPath is the nail . In this way , it is notice than XPath setting , if one datasource node 's XPath setingg is mistake , just like the node bind mistke XML node or missing , all of children is missing .

It fact , XML document is not create for report , so report tool maybe leave XML document for more data , it maybe get data from another XML document or execute query on RDBMS . This character is test agility of report tool .

We know , RSS document is a kind of XML document , so at there , we use RSS documment as an example to discuss how to read data from XML document . At first , we realize the structure of RSS document . there are a RSS document which url is . it's root is rss , then has a channel child node that include some base information for rss document , then has some item node that list all of article . item node include some information of an article , the content of wfw:commentRess node is an url of feedback rss document for one articel . your can use this url to load feedback rss document , base on RSS document structure , we can define a report datasource structure and the mapping from datasource to XML document .

The rss document has treee-layer structure , and need load feedback document dynamic for read more data , this work is complex ,old two-layer datasource model can not handle this work . this work complete by the following steps .

  1. Load XML document as a mainly XML document , instance a System.Xml.XmlDocument object , and the object is the jumping-off point.
  2. Use XPath "rss" , enumerate elements which match the xpath , Obviously , only get one element , then set current element as rss element.
  3. At current element , use XPath "channel/title" to get the title of web site , use "channle/link" to get the url of site , "channle/description" to get site description.
  4. use XPath "channel" , enumerate elements , obviously , only one "channel" element match , then set "channel" elemenet as current element .
  5. Use XPath "item" , enumerate elements which match this xpath , in each enumerate , set one item element as current element .
  6. use XPath "title" to get title of article , "link" to get the url of article , "author" to get author's name , "pubDate" to get the publish date , "description" to get description of article , "slash:comment" to get the number of feedback , "wfw:ommentRss" to get the url of feedback rss document.
  7. when handle "wfw:commentRss" element , report tool use it's cotent as an url , load xml document dyanmic , and use XPath "rss/channel/item" to enumerate element , in each enumerate , set on matched element as current element .
  8. use "author" to get the author's name of feedback , use "pubDate" to get date of feedback , "description" to get content for feedback.
  9. because in rss document , "description" contain HTML string , so it is need to parse the html string and get text content .

From those steps , you can see that , each datasource node bind one element of XML document , and during get feedback data , report tool execute XML's jump , it jump from mainly XML document to feedback XML document . And because of handle tree structure , use recursion , many program state information save in call-stack automatic , we need not handle those .

It report tool can connection database of site , it can jump from author element to database , query database and get some registe information of author . In fact , each node in the datasource tree can execte jump between in XML-XML , XML-RDBMS , RDBMS-XML , this character increase the power of report tool greatly.

If a system is a 100% XML application , Report tool can jumping in XML documents and collect report data ,then all of database query , business logic run in application internal , report tool do not take care about it .If system is strong , report module is strong , system can modify freely , just only maintain XML document structure , the report module need not modify . When some report's data is very complex and out of range of report tool , developer can develop a special XML document to provide report data . Before , system use report tool's API to send report data , but now use an XML doucment send data to report tool , in this case , the boundary of system is clearly and safe , it is embodiment of XML WebService 's idea . And this method can use to other domain , no only for report .

The discuss limited B/S system , but we can assume , after recast , C/S system can send XML document to report tool in some way .

From the article , we can recognize that XML is a new mainland of report data , and I am already work out a report tool which name is XReport to realization this idea primary . you can download it from .


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

yuan yong fu
Web Developer duchang soft
China China
yuan yong fu of duchang soft , come from CHINA , 2008 Microsoft MVP,Use GDI+,XML/XSLT, site:

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