Version 5.8.0

# XPath Expressions

## What is XPath?

XPath is a language for navigating XML trees and querying data. Since the Publisher’s input data is in XML format, XPath is the central tool for accessing elements, attributes and text. Examples: “give me all articles with a certain attribute” or “how many articles are in this article group?”.

For a general introduction to XPath, see the tutorial at W3Schools.

## Where are XPath expressions used?

The Publisher accepts XPath expressions in two places:

1. In the attributes `select` and `test` — the value is interpreted directly as XPath.
2. In all other attributes — curly braces (`{` and `}`) force an XPath expression.

    <Textblock width="{ $width }">
      <Paragraph>
        <Value select="."/>
      </Paragraph>
    </Textblock>

The width is read from the variable `$width`, the paragraph content is the text value of the current data node.

## Supported expressions

- Numbers and text: `"5"`, `'hello world'` — returned directly.
- Arithmetic operations: `*`, `div`, `idiv`, `+`, `-`, `mod`. Example: `( 6 + 4.5 ) * 2`
- String concatenation: `||` concatenates strings. Example: `'Hello' || ' ' || 'World'` returns `Hello World`.
- Variables: `$column + 2`
- Current node (dot operator): `. + 2`
- Child elements: `productdata`, `*`, `foo/bar`, `node()`
- Parent node: `../`
- Attributes: `@a`, `foo/@bar`
- Filters: `article[1]` selects the first `article` child element.
- Comparisons: `<`, `>`, `<=`, `>=`, `=`, `!=`. Note: `<` must be written as `&lt;` in XML.
- If/then/else: `if (...) then ... else ...`
- For expressions: `for $i in (1,2,3) return $i * 2` or `for $i in 1 to 3 return $i * 2`
- Arrays: `[1, 2, 3]` or `array { 1 to 3 }`. Access via lookup: `$arr?2`. See Arrays and Maps.
- Maps: `map { 'name': 'value' }`. Access via lookup: `$map?name`. See Arrays and Maps.
- Axes: `preceding-sibling`, `parent`, `descendant-or-self`, `following-sibling` etc.

## XPath and namespaces

The speedata Publisher ignores XML namespaces by default. This is usually very helpful, as namespaces are not always easy to handle.

The XML file:

    <bar:data xmlns:bar="somenamespace">
        <bar:child>
            <bar:sub>sub</bar:sub>
        </bar:child>
    </bar:data>

can be addressed in the layout as follows:

    <Layout xmlns="urn:speedata.de:2009/publisher/en"
        xmlns:sd="urn:speedata:2009/publisher/functions/en">

        <Record element="data">
          ...

although the namespace of the root element is `somenamespace`.

With `<Options namespaces="strict" />` you can change this so that the namespace must be specified for `<Record>` and `<ProcessNode>`:

    <Layout xmlns="urn:speedata.de:2009/publisher/en"
        xmlns:sd="urn:speedata:2009/publisher/functions/en"
        xmlns:sn="somenamespace">

        <Options namespaces="strict" />

        <Record element="sn:data">
            <PlaceObject>
                <Textblock>
                    <Paragraph>
                        <Value select="local-name()"></Value>
                    </Paragraph>
                </Textblock>
            </PlaceObject>
        </Record>
    </Layout>

It is important that the namespace matches, the prefix (here: `sn`) is freely selectable as long as it is linked to the namespace.

`<ProcessNode>` works similar:

    <ProcessNode select="*:child" />
    <ProcessNode select="sn:child" />
    <ProcessNode select="sn:*" />
    <ProcessNode select="*" />

call the child element `bar:child`, as the namespaces of `sn` (from the layout) and `bar` (from the data) match. `*` is a ‘wildcard’ here, so it matches all names.

`<ProcessNode select="child" />` will not work in the above case, as the empty namespace from the layout is `urn:speedata.de:2009/publisher/en` and does not match the namespace from the data.

You must also use namespaces in the XPath queries if they are specified in the data:

    <Message select="count(sn:sub)" />

writes 1 to the log file. Without namespace a 0, as no element sub with the preset namespace is found.

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