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" />

---

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>