Compound Steps

Compound Steps contain subpipelines and they allow, amongst other things, nestings. A subpipeline may contain any number of further subpipelines.

example of a Compound Step in XProc

Figure: example of a Compound Step in XProc

Instead of an Atomic Step as shown in the figure, also a further Compound Step could be displayed, which means a further complete pipeline.

The important Compound Steps

In the following the important Compound Steps are introduced and each is clarified with the aid of an example.

p:for-each

<p:for-each name? = NCName>
  ((p:iteration-source? &
   (p:output |
   p:log)*),
  subpipeline)
</p:for-each>

The <p:for-each> step is a loop implementation under XProc. In that way documents which are assigned to this step are processed sequentially in a subpipeline. The input has to be provided by a preceding step as a sequence (which means it has to contain several documents). Alternatively, the content could also be provided by <p:iteration-source>.

<p:iteration-source select? = XPathExpression>
   (p:empty |
   (p:pipe |
   p:document |
   p:inline |
   p:data)+)?
</p:iteration-source>

<p:iteration-source> is only available in <p:for-each>. As attribute a XPath expression can be used which addresses desired contents from the initial document (from the input port). Alternatively, contents can also be loaded or created via <p:document>, <p:inline> and <p:data>. Then, the imported documents are successively processed in the subpipeline.

Example

In the following example the functionality of the <p:for-each> steps is demonstrated.

<?xml version="1.0" encoding="UTF-8"?>
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" xmlns:c="http://www.w3.org/ns/xproc-step" version="1.0">
  <p:input port="source">
    <p:document href="FilmCollection.xml"/>
  </p:input>
  <p:output port="result" sequence="true"/>
  <p:for-each>
    <p:iteration-source select="//Year"/>
    <p:output port="result"/>
    <p:rename match="/Year" new-name="Date"/>
  </p:for-each>
</p:declare-step>

The data to be processed is defined by the <p:iteration-source> step. It states that all “Year“ elements of the imported source document shall be processed loopwise. They are sent successively to the <p:rename> step which renames the element as “Date“.

p:viewport

<p:viewport
  name? = NCName
  match = XSLTMatchPattern>
  ((p:viewport-source? &
   p:output? &
   p:log?),
  subpipeline)
</p:viewport>

By the <p:viewport> Compound Step certain parts of a document can be selected by an appropriate XSLT expression in order to process them in a subpipeline. Alternatively, the desired content can also be provided by <p:viewport-source>.

<p:viewport-source>
   (p:pipe |
   p:document |
   p:inline |
   p:data)?
</p:viewport-source>

<p:viewport-source> is only available as part of <p:viewport>. Here, a document must be indicated. This can be realised by the elements <p:pipe>, <p:document>, <p:inline> or <p:data>. If no document is indicated, a dynamic error will be generated.

Example

In the following example only part of the document shall be processed.

<?xml version="1.0" encoding="UTF-8"?>
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" xmlns:c="http://www.w3.org/ns/xproc-step" version="1.0">
  <p:input port="source">
    <p:document href="FilmCollection.xml"/>
  </p:input>
  <p:output port="result"/>
  <p:viewport match="/FilmCollection/Film/Title">
    <p:wrap match="/" wrapper="test"></p:wrap>
  </p:viewport>
</p:declare-step>

The XSLT expression in the “match“ attribute of the <p:viewport> step addresses all “Title“ elements from the source document. This part of the document is transfered into the subpipeline of <p:viewport>, in the example only the <p:wrap> step. There, all “Title“ elements are renamed as “test“.

p:group

<p:group name? = NCName>
   ((p:output |
   p:log)*,
  subpipeline)
</p:group>

<p:group> is a so-called wrapper for an accumulation of several steps. This wrapper compounds these steps and must be applied, for example, in the Multi-Container Step <p:try> within the try area.

Example

In the following example a <p:group> step is demonstrated.

<?xml version="1.0" encoding="UTF-8"?>
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" xmlns:c="http://www.w3.org/ns/xproc-step" version="1.0">
 <p:input port="source">
  <p:empty/>
 </p:input>
 <p:output port="result"/>
 <p:group>
  <p:identity>
   <p:input port="source">
    <p:inline>
     <doc>Example</doc>
    </p:inline>
   </p:input>
  </p:identity>
 </p:group>
 <p:identity/>
</p:declare-step>

In this example the <p:identity> step is enclosed with a <p:group> element. The shown source text shall only demonstrate the use of the step.

<< back

next >>