We now discuss the imperative portion of the AlarmActuator task. The complete code listing for the Java class corresponding to this task is shown in Figure 5.15. The declarative part of this ATaG program requires this task to be hosted on a root node with a fixed node ID, say, zero. This node will typically correspond to a supervisor station. All data items of type Fire will be routed to this node per the ATaG specification. The data item of type Fire is produced by the Monitor task only when a temperature gradient that exceeds the prespecified threshold is detected. Hence, a receipt of this data item at the supervisor nodes indicates that an abnormal condition exists somewhere in the sensor network. When the Monitor task produces the data item on a particular node where the abnormality is detected, it does not explicitly add the node information to the data item. However, the DART runtime system tags each data item with the location and time of its production. The functionality in lines 1-20 of Figure 5.15 has been discussed earlier for other abstract tasks. The r u n 0 method of the AlarmActuator is straightforward. This method is invoked whenever an instance of type Fire is added to the data pool of the node that hosts this abstract task-that is, the supervisor node. The semantics of any-data firing rule guarantee that whenever the run (1 method is invoked, a data item of type Fire exists in the data pool and the call to getData() in line 22 never returns null. The check for a null return

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package atag. application; import atag . runtime . * ; import atag.runtime.config.*; import visualizer . * ; public class AlarmActuator implements Runnable C DataPool m-datapool ; private Config m-mystate; private mCUI m-GUI; private GUIMessage m-guiklessage; public AlarmActuator (DataPool dp, Conf ig myconf ig , NetworkArchitecture t-networkArchitecture, mCUI t-CUI) I la-datapool = dp; m-mystate = myconfig; m-GUI = t-CUI;

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public void r u n 0 DataItem t-dataItem = m-dataPool.getData( IDConstants . T-ALARHACTUATOR , 1DConstants.D-FIRE); Fire t-fire = null; if (t-dataItem ! = null) t-f ire = (Fire) t-dataItem. core ( 1 ; int nodeOnFire = t-dataItem.originID0; m-guinessage = new C U I M e s s a g e ( m - m y S t a t e . m y I D 0 , CUIHessage. GUIH-NODEOUTPUT , m-guiMessage.setNodeOutput("Node," + nodeOnFire + "uisuONuFIRE! " ) ; m-CUI.send(m-guiMessage);

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value in line 26 is added as a precautionary measure to detect the correctness of the implementation of the data pool manager. When the data item is retrieved from the pool, its origin ID is determined by a call to originID0 of the data item. Note that this method is supported by the DataItem class and not by any application-specific data item such as F i r e . The origin information is automatically added to the data item in the DART runtime. Currently, the only result of receiving the data item is a notification to the visualization interface. The ID of the node "on fire" is passed to the

package atag. application; import java. io. Serializable; public class TargetAlert implements Serializable { private int m-targetDistance; private boolean acquired ; public void setAcquired (boolean flag) { acquired = f l a g ;

public boolean acquired (1 { return acquired;

public void setDistance(int d) { m-targetDistance = d;

public int d i s t a n c e 0 4 return m-targetDistance;

There are two types of data items in the ATaG program for object detection and tracking. The TargetAlert data item is produced by the sampler task whenever the reading of the acoustic sensor is above a certain threshold. This data item indicates that an object of interest has been detected in the vicinity of the node where this data item is produced. The code listing for the corresponding class is shown in Figure 5.16. This data item has two variables; one correspondingto the distance of the target from this node (line 6) and the other indicating whether this data item corresponds to the acquisition of a target or