Samples XSLT Transformations

openHAB allows you to post HTTP queries over the internet, and to put the received data in items that you can use in your rules. In most cases, you will get the information you need into a XML structured document, and you need a way to extract only the value you want: here is where XSLT transformations come in our help. XSLT is a standard method to transform an XML structure into a document with the structure you want. You can find a very good tutorial here: XSLT tutorial at W3Schools

In the following examples:

• the directive xsl:output says that the incoming document must be transformed into another XML-like document, without XML header (the part)
• the directive template specify a rule to apply when a specific XML node type is found. The template to match is contained in the match="/" clause, where "/" means "any type of node", so the whole document.
• inside the template directive we find the rule, in this case a value to extract from the selected node. In the first example, we want to extract the value temp from the node yweather:condition. Indeed, if we look at the syntax of the Yahoo Weather service, we can see that the weather conditions are returned into a XML document that contains a string like that:

<yweather:condition  text="Mostly Cloudy"  code="28"  temp="50"  date="Fri, 18 Dec 2009 9:38 am PST" />

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Once you have defined your transformations, you can bind them with items in the items definition file.

The binding has the syntax:

{ http="<[URL:INTERVAL:XSLT(FILENAME)]" }

where URL is the url where the relevant data can be retrieved, INTERVAL is the interval in milliseconds between two queries, and FILENAME is the name of the related transformation file.

Don't forget the initial 'less than' symbol !!

Here is an example:

Number Weather_Temperature "Outside Temperature [%.1f °C]" <temperature> (Weather_Chart) { http="<[http://weather.yahooapis.com/forecastrss?w=638242&u=c:60000:XSLT(yahoo_weather_temperature.xsl)]" } 

Here below you can find various examples of transformation files for the Yahoo Weather Forecast service.

---

Yahoo Weather - temperature

<?xml version="1.0"?>
<xsl:stylesheet 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
   <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
    
   <xsl:template match="/">
      <xsl:value-of select="//yweather:condition/@temp" /> 
   </xsl:template>
    
</xsl:stylesheet>

Yahoo Weather - feels like temperature

<?xml version="1.0"?>
<xsl:stylesheet 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
   <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
    
   <xsl:template match="/">
      <xsl:value-of select="//yweather:wind/@chill" /> 
   </xsl:template>  
    
</xsl:stylesheet>

Yahoo Weather - humidity

<?xml version="1.0"?>
<xsl:stylesheet 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
   <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
    
   <xsl:template match="/">
      <xsl:value-of select="//yweather:atmosphere/@humidity" />
   </xsl:template>
    
</xsl:stylesheet>

Yahoo Weather - sunrise

<?xml version="1.0"?>
<xsl:stylesheet 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
   <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
    
   <xsl:template match="/">
      <xsl:value-of select="//yweather:astronomy/@sunrise" />
   </xsl:template>
    
</xsl:stylesheet>

Yahoo Weather - sunset

<?xml version="1.0"?>
    <xsl:stylesheet 
            xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
            xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
            <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
    
            <xsl:template match="/">
                    <xsl:value-of select="//yweather:astronomy/@sunset" />
            </xsl:template>
    
    </xsl:stylesheet>

Yahoo Weather - weather text

<?xml version="1.0"?>
    <xsl:stylesheet 
            xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
            xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
            <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
    
            <xsl:template match="/">
                    <xsl:value-of select="//item/yweather:condition/@text" />
            </xsl:template>
    
    </xsl:stylesheet>

Yahoo Weather - wind speed

<?xml version="1.0"?>
    <xsl:stylesheet 
            xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
            xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
            <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
    
            <xsl:template match="/">
                    <xsl:value-of select="//yweather:wind/@speed" />
            </xsl:template>
    
    </xsl:stylesheet>

Yahoo Weather - forecast tomorrow

<?xml version="1.0"?>
<xsl:stylesheet 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
   <xsl:output indent="yes" method="text" encoding="UTF-8" omit-xml-declaration="yes" />
    
   <xsl:template match="/">
      <xsl:value-of select="//item/yweather:forecast[1]/@text" />
      <xsl:text>, Low: </xsl:text>
      <xsl:value-of select="//item/yweather:forecast[1]/@low" /> 
      <xsl:text>°C, High: </xsl:text>
      <xsl:value-of select="//item/yweather:forecast[1]/@high" /> 
      <xsl:text>°C</xsl:text>
   </xsl:template>
       
</xsl:stylesheet>

Yahoo Weather - forecast day after tomorrow

<?xml version="1.0"?>
<xsl:stylesheet 
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
   xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0" version="1.0">
    
   <xsl:output indent="yes" method="text" encoding="UTF-8" omit-xml-declaration="yes" />
    
   <xsl:template match="/">
      <xsl:value-of select="//item/yweather:forecast[2]/@text" />
      <xsl:text>, Low: </xsl:text>
      <xsl:value-of select="//item/yweather:forecast[2]/@low" /> 
      <xsl:text>°C, High: </xsl:text>
      <xsl:value-of select="//item/yweather:forecast[2]/@high" /> 
      <xsl:text>°C</xsl:text>
   </xsl:template>
    
</xsl:stylesheet>

Relay board from "Progetti HW SW" but also a good example for XSLT transformation.

XML file:

<response>
  <led0>1</led0>
  <led1>1</led1>
  <led2>1</led2>
  <led3>1</led3>
  <led4>0</led4>
  <led5>0</led5>
  <led6>0</led6>
  <led7>0</led7>
  <btn0>up</btn0>
  <btn1>up</btn1>
  <btn2>up</btn2>
  <btn3>up</btn3>
  <btn4>dn</btn4>
  <btn5>up</btn5>
  <btn6>up</btn6>
  <btn7>up</btn7>
</response>

Translation:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output indent="yes" method="xml" encoding="UTF-8" omit-xml-declaration="yes" />
  <xsl:template match="/">
     <xsl:apply-templates select="response/led1"/>
   </xsl:template>
   <xsl:template match="*">
     <xsl:choose>
        <xsl:when test="self::node()[node()=1]">ON</xsl:when>
        <xsl:when test="self::node()[node()=0]">FALSE</xsl:when>
        <xsl:when test="self::node()[node()='up']">UP</xsl:when>
        <xsl:when test="self::node()[node()='dn']">DOWN</xsl:when>
        <xsl:otherwise><xsl:value-of select="@service"/></xsl:otherwise>
     </xsl:choose>
  </xsl:template>
</xsl:stylesheet>