== Resource Access Interface ==

There is no single resource access interface in the SENSEI architecture, instead each resource description published by a REP includes information about the interface(s) available to access it, for example the URL and interface description. In order for Resource Users to easily access resources, a set of well-known resource interfaces have been defined for sensor, parameter, actuator and code-update resource types. 

How to connect to these URLs using REST is described in the [[RuConnecting| Connecting a Resource User ]] section.
A short example of how a response looks like is this:

{{{
#!xml
<rdf:RDF>
   <nmib:Location mo:direction="B" mo:hasTimeStamp="17 Oct 2010 12:57:00" 
         mo:latitude="44.8300183" mo:line="24" mo:longitude="20.4559783" 
         mo:nextStationDistance="42.11" mo:nextStationID="B14" 
         mo:nextStationName="Dorcol" 
         rdf:about="http://www.resource-provider-456.com/resources#location"/>
</rdf:RDF>
}}}

All responses are in the XML-RDF format so that the Semantic Query Analyser can work with them. 
How a Resource User gets this reference is by either querying an SQR or an RD. (see [[RuRli| the
RLI Interface). Of course another way would be to browse an RD directly (/rd url) and to read all
resources available, but this works well only for small systems.

The URL is provided by the Rep-Locator entry of the Resource Directory Description. 

A resource may have one or more such urls, and even publish URL behind company proxies.
{{{
#!xml
<REP-Locator>
http://195.178.44.184/rephandler/gps/358278005846910
</REP-Locator>
}}}

It is up to the client to detect if it will use IPv6 or IPv4 addresses and to select 
the best connected resource.

The whole RD entry looks like this:
{{{
#!xml
<Resource-Description>
−
<Resource-ID>
urn:sensei:ericsson.com:EnvironmentalSensors:busgps:358278005846910
</Resource-ID>
<Name>Bus Location Sensors in Belgrade</Name>
<Storage-ID>6</Storage-ID>
<Expiration-Time>11-01-01T00:00:00+00:00</Expiration-Time>
<Tag>Bus</Tag>
<Tag>GPS</Tag>
<Tag>Sensor</Tag>
<Tag>Belgrade</Tag>
<Tag>24</Tag>
<Tag>358278005846910</Tag>
−
<RAI-Description>
<RAI-ID>0</RAI-ID>
<Description>GET returns sensor values (RDF)</Description>
−
<REP-Locator>
http://195.178.44.184/rephandler/gps/358278005846910
</REP-Locator>
</RAI-Description>
</Resource-Description>
}}}

By using URLs to get sensor data, you can enforce AAA and Billing easily and you can use any language to query the resource. Ofcouse, you have to parse XML. A small example of a RAI Client is the monitoring plugin of the WP4 Check Service.

{{{
#!java
	/**
	 * <p>res:hasDecimalValue="26.80"</p>
	 * 
	 * @see lia.util.DynamicThreadPoll.SchJob#doProcess()
	 */
	@Override
	public Object doProcess() throws Exception {
		if (configGet == null) {
			return null;
		}
		
		Vector<Result> results = new Vector<Result>();
		HashMap<String,URL> sensors = configGet.getSensorUrls();
		for (String name : sensors.keySet()) {
			URL url = sensors.get(name);
			String sResult = configGet.post(url, null);
			
			String sPattern = "res:hasDecimalValue=\"((.)*)\"";
			Pattern pattern = Pattern.compile(sPattern,
				Pattern.UNIX_LINES | Pattern.DOTALL);
			Matcher matcher = pattern.matcher(sResult);
		
			try {
				if (matcher.find()) {
					String data = matcher.group(1);
					
					if (data != null) {
						Double value = new Double(data);

	                                        //Store Result					
						Result result = new Result(Node.getFarmName(), 
								Node.getClusterName(), 
								name, ModuleName, ResTypes);
						result.time = System.currentTimeMillis();
						result.param[0] = value;
						
						results.add(result);
						if (logger.isLoggable(Level.INFO)) {
							logger.info("" + result.toString());
						}
					}
				}
			} catch (NumberFormatException e) {
				
			} catch (NullPointerException e) {
				
			}
		}
		
		return results;
	}
}}}