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 Connecting a Resource User section. A short example of how a response looks like is this:

<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.

<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:

<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.

        /**
         * <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;
        }