PB138 — Advanced XML Processing

(C) 2019 Masaryk University -- Tomáš Pitner, Luděk Bártek, Adam Rambousek

Outline

  • Types of transformations

  • XML pipelining

XML Transformations

  • An XML transformation language is a programming language designed specifically to transform an input XML document to an output document which satisfies some specific goal.

  • There are two special cases of transformation:

    • XML to XML — the output document is an XML document.

    • XML to Data — the output document is a byte stream.

XML Pipeline

  • XML Pipeline connects of XML processes, especially XML transformations and XML validations.

  • For instance, given two transformations T1 and T2, the two can be connected so that:

    1. input XML document

    2. is transformed by T1 and then

    3. output of T1 is fed as input document to T2

  • Simple pipelines like the one described above are called linear: a single input document always goes through the same sequence of transformations to produce a single output document.

XML Pipeline operations

  • Linear operations

  • Non-linear operations

Linear operations

  • Micro operations

  • Document operations

  • Sequence operations

Linear: Micro-operations

  • Operate at the inner document level:

    • Rename — renames elements or attributes without modifying the content

    • Replace — replaces elements or attributes

    • Insert — adds a new data element to the output stream at a specified point

    • Delete — removes an element or attribute (also known as pruning the input tree)

    • Wrap — wraps elements with additional elements

    • Reorder — changes the order of elements

Linear: Document operations

They take the input document as a whole:

  • Identity transform — makes a verbatim copy of its input to the output

  • Compare — it takes two documents and compare them

  • Transform — execute a transform on the input file using a specified XSLT file

  • Split — take a single XML document and split it into distinct documents

Linear: Sequence operations

They are mainly introduced in XProc and help to handle the sequence of documents as a whole:

  • Count — it takes a sequence of documents and counts them

  • Identity transform — makes a verbatim copy of its input sequence of documents to the output

  • Split-sequence — takes a sequence of documents as input and routes them to different outputs depending on matching rules

  • Wrap-sequence — takes a sequence of documents as input and wraps them into one or more documents

Non-linear operations

  • Conditionals — where a given transformation is executed if a condition is met while another transformation is executed otherwise

  • Loops — where a transformation is executed on each node of a node set selected from a document or a transformation is executed until a condition evaluates to false

  • Tees — where a document is fed to multiple transformations potentially happening in parallel

  • Aggregations — where multiple documents are aggregated into a single document

  • Exception Handling — where failures in processing can result an alternate pipeline being processed

What is XProc?

Benefits of XProc

  • XProc takes care of orchestrating all the activities

  • XProc is a standard way of expressing processing activities

  • Since an XProc document is an XML document, you can send it around, transform it, mine it, store it, just like any other XML document

XProc Example - identity

<?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:inline>
         <doc>Hello World!</doc>
      </p:inline>
   </p:input>
   <p:output port="result"/>
   <p:identity/>
</p:declare-step>

XProc Example - validation

<p:declare-step xmlns:p="http://www.w3.org/ns/xproc"
                name="xinclude-and-validate"
                version="1.0">
  <p:input port="source" primary="true"/>
  <p:input port="schemas" sequence="true"/>
  <p:output port="result">
    <p:pipe step="validated" port="result"/>
  </p:output>
  <p:xinclude name="included">
    <p:input port="source">
      <p:pipe step="xinclude-and-validate" port="source"/>
    </p:input>
  </p:xinclude>
  <p:validate-with-xml-schema name="validated">
    <p:input port="source">
      <p:pipe step="included" port="result"/>
    </p:input>
    <p:input port="schema">
      <p:pipe step="xinclude-and-validate" port="schemas"/>
    </p:input>
  </p:validate-with-xml-schema>
</p:declare-step>

XProc Example - A validate and transform pipeline

<p:pipeline xmlns:p="http://www.w3.org/ns/xproc" version="1.0">
  <p:choose>
    <p:when test="/*[@version &lt; 2.0]">
      <p:validate-with-xml-schema>
        <p:input port="schema">
          <p:document href="v1schema.xsd"/>
        </p:input>
      </p:validate-with-xml-schema>
    </p:when>
    <p:otherwise>
      <p:validate-with-xml-schema>
        <p:input port="schema">
          <p:document href="v2schema.xsd"/>
        </p:input>
      </p:validate-with-xml-schema>
    </p:otherwise>
  </p:choose>
  <p:xslt>
    <p:input port="stylesheet">
      <p:document href="stylesheet.xsl"/>
    </p:input>
  </p:xslt>
</p:pipeline>

XProc Processors

  • XML Calabash (not to be confused with Android/iOS-Calabash)

  • Calumet

  • Tubular

  • xmlsh

XML Calabash

Resource on XML Pipeline