Friday, January 28, 2011

XPath: An Introduction

XPath is a query language used to navigate through an XML structure. In other words, assume you have the following folders on your C drive: Folder 1, Folder 2 that is inside Folder 1, Folder 3 that is stored inside Folder 2. Now to access Folder 3, you would probably type C:\Folder 1\Folder 2\Folder 3 in your run command. Likewise, XPath can be considered as a language that would help you navigate your XML document and locate specific XML sections in your document.

Let us consider a simple XML structure as below:

  <ProductLine name="Product Line A">
      <Product type="Product Type A">A</Product>
      <Product type="Product Type A">B</Product>
      <Product type="Product Type A">C</Product>
  <ProductLine name="Product Line B">
     <Product type="Product Type B">D</Product>
     <Product type="Product Type B">E</Product>
     <Product type="Product Type B">F</Product>
 <ProductLine name="Product Line C">
    <Product type="Product Type C">G</Product>

Using XPath you can traverse the structure using the following XPath Expressions:

node - Select all the nodes with the name "node" Example: Products would return all nodes with node name Product.
/ - Select the root node. In our example XML this would return the root Products node.
// - Select all the nodes in the document from the current node that match the defined condition. //ProductLine would return all ProductLine nodes assuming we are at the root node.
@ - Select attributes. ProductLine[@name = 'Product Line A'] would return Product Line nodes with name value set to Product Line A.

XPath Predicates: XPath Predicates allow you to select nodes containing defined values.

node[1] - Select the first node of type node. ProductLine[1] would return the first Product Line node.
node[@type='Type 1'] - Select nodes that have type attribute with value Type 1.
node[@value > 100] - Select nodes that have value attribute with value > 100.

There are many more such expressions and predicates that you can use. But not all are supported by CMS. Only a subset of the XPath expressions and predicates are supported by CMS.

In my next article I will write about how to get the XML of the data generated by Cognos.Note, this XML is not the same as the report XML. The report XML defines the report specification while the XML we are dealing with in CMS defines the report output or rather the report data along with the styles that go with the data.

CMS XPath Examples:

Consider a report that has 2 pages (Yearly Revenue Page, Revenue Detail Page). The Yearly Revenue Page displays a revenue chart and the Revenue Detail Page displays 2 lists - Sales Region Revenue and Product Revenue.

To get all the nodes of type list.


To get all the column titles of the list nodes.


To access the Region Sales list on Page 2.


To select Row 1 of Group 1 (2004) of Region Sales list.


To get all Asia Pacific rows of Region Sales list.

http://localhost:81/cognos84/cgi-bin/cognos.cgi/rds/reportData/report/i754384CF51C94873A34DABCF36108B16?xpath=/document/page[2]/body/item[1]/lst/group/grp/row[cell/item/txt/val='Asia Pacific']

To get row 2 in each group of Region Sales list.




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Anonymous said...

I suspect it's just me, but can't I use an XPATH in the URL to find the report in the first place? How would the syntax be to find reports that have "QUARTERLY" in the name?