3 Managing Filters

3.1.1 Device- and Device Group-Level Filtering

Filters can be attached to either a specific device or to a device group. Some filters are written as group-level filters and can only be attached to a device group. Likewise, some filters are written only for device-level filtering and only function if they are attached to a specific device. The filter object implements three levels of filtering:

• Pre-Device Filtering

• Post-Device Filtering

• Device Group Filtering

Pre-Device Filtering

Pre-device filtering provides filtering against a batch of pass-in events before they are routed to the Oracle Sensor Edge Server device.

Post-Device Filtering

Post-device filtering provides any filtering against the events before they are merged up to a device group.

Device Group Filtering

Device group filtering provides filtering against events before they are delivered to an edge client.

The Oracle Sensor Edge Server enables you to add filters that provide pre-device and post-device filtering. For more information on device group- and device-level filtering, refer to Section 3.3.1.

3.2.1 Configuring the Check Tag ID Filter

A Check Tag is any normal tag used to test if the device (in this case, a reader) is reading tags. Because the Check Tag itself should be physically located within the field of the reader, it should always be read; when other tags move through the field of the reader, the device also reads the Check Tag in conjunction with them.

The Check Tag ID Filter ensures that the device reads a Check Tag periodically. Using this filter enables you to check the status of a driver, its corresponding reader, and attached antennae. Because the Check Tag ID Filter is used solely for diagnostic purposes, it does not provide any events for dispatching to client devices. Instead, this filter generates an event if it does not detect that the device has read a Check Tag for a specified period of time.

Table 3-2 describes the parameters (and associated values) of the Check Tag ID filter.

To define the parameters for the Check Tag ID Filter, you must note the ID of the Check Tag itself (which must be placed within the field of the reading device). Enter this ID as the String value of <CheckTagId>. If the filter does not detect that a device has read a Check Tag bearing the specified ID for the period defined in the <TagCheckTimeWindow> parameter, it generates an event. Table 3-3 describes the signature of the generated event. Refer to Section 1.1.2 for more information on the Event type.

3.2.2 Using the Cross-Reader Redundant Filter

The Cross-Reader Redundant Filter blocks redundant events that are sent from the devices of a device group and does not generate any events. This filter considers events redundant if it finds they have the same tag ID.

The Cross-Reader Redundant Filter is for group-level filtering only; it performs no functions if applied to a device. This filter has no parameters to configure.

3.2.3 Using the Debug Filter

The Debug Filter traces events passing through the system. Upon receiving events from its associated device, this filter writes events to a log file. This filter has a single parameter called <EventOutputFile>. To define this parameter, enter the full path of the log file to which the Debug Filter writes events. (The server must make this file writable.) The format of the Debug Filter's output is:

"Devicename: <devicename> Type: <type> Subtype: <subtype> EventTime: <time>TagIds:<tagid(,tagid)*>Data:<dat(,data)*>\n"

Each event is on a separate line; each line is separated by a newline character (LF or CRLF, depending on the operating system). The <time> value is a long as returned by the time(2) call.

This filter can only be attached to a device, not to a device group.

3.2.4 Configuring the Pass Filter

When a tag passes through the range of transmission, or through the gateway of a device reader, it generates a series of "tag is seen" events. The device reports these events periodically, starting when the tag enters the transmission field. The reporting stops when the tag moves out of the reader field.

Applications often do not require the series of events that a device reader generates; instead, these applications only need to know that a tag has passed through a device's gateway or range of transmission. The Pass Filter applies to such situations, as it reduces all of the "tag is seen" events into single events for each unique tag that passes through the field of a reader device.

The Pass Filter has one parameter, <ExitEventThresholdTime>. To define this parameter, enter the time (an int value), in milliseconds, since the device last read the tag before it is considered to have moved out of the device's transmission field. The parameter settings, which range from 50 milliseconds to under two seconds, dictate the frequency (that is, the reader cycle) in which the device reports these "tag is seen" events. If you set this frequency too high, such as to two seconds, then the device may miss the tag altogether.

When the device first reads a tag, the Pass Filter caches the tag's ID (tagid), notes the time that the tagid was read into the cache, and then immediately sends the pass-through event. The filter blocks subsequent reads for this cached tagid. Each time the filter receives a new read from the device, it updates the time that it read the tagid into the cache. If the sum of the caching time and the value set for <ExitEventThresholdTime> is less than the current time, then the Pass Filter clears the tagid from the cache. The next time the device reads this tag, the filter considers it a new event, caches its tagid and sends out a new pass-through event. Refer to Section 1.1.2 for more information on the Event type.

Table 3-3 describes the signature of the pass-through event.

3.2.5 Configuring the Shelf Filter

The Shelf Filter is a device-level filter that generates events when a tag is detected within the field of a reader or when the tag has left the field. Like the Pass Filter, the Shelf Filter has a single parameter, <ExitEventThresholdTime>. To define this parameter, enter the time (an int value), in milliseconds, since the device last read the tag before it is considered to have moved out of the device's transmission field. Unlike the Pass Filter, however, the Shelf Filter silently clears its cache once the interval defined for the <ExitEventThresholdTime> parameter elapses and does not generate an event.

3.2.6 Configuring the Pallet Pass Thru Filter

The Pallet Pass Thru Filter collects all of the events received during a specified period and sends them out as a single event. When a pallet or container passes through a gateway or through the field of transmission of a reader device, this filter generates a single event for all of these tags. This filter enables you to see what items a container or pallet may hold.

The Pallet Pass Thru Filter includes the following parameters:

• <ExitEventThresholdTime>

• <EventCollectControlTime>

<ExitEventThresholdTime>

To define this parameter, enter the time (an int value), in milliseconds, since the device last read a tag before it is considered to have moved out of the device's transmission field. The parameter settings, which range from 50 milliseconds to under two seconds, dictate the frequency (that is, the reader cycle) in which the device reports these "tag is seen" events. If you set this frequency too high, such as to two seconds, then the device may miss the tag altogether.

<EventCollectControlTime>

To define this parameter, enter the time (an int value), in milliseconds, for a device to complete a reading cycle of the tags included in a pallet or container before starting a new reading cycle. When this time elapses, the reading cycle concludes (that is, the device has read all of the new tags) and the Pallet Pass Thru Filter then generates an event with the following signature (described in Table 3-6). Refer to Section 1.1.2 for more information on the Event type.

3.2.7 Configuring the Pallet Shelf Filter

The Pallet Shelf Filter collects all of the events received during a set interval and then sends them as a single event. This filter enables you to identify when new containers or pallets holding many items enters an area, or exits the field or gateway of a device reader.

The Pallet Shelf Filter has the following parameters:

• <ExitEventThresholdTime>

• <EventCollectControlTime>

<ExitEventThresholdTime>

To define <ExitEventThresholdTime>, enter the time (an int value), in milliseconds, from the last time that the device read the tag before it is considered to have moved out of the device's transmission field. The Pallet Shelf Filter silently clears its cache once the interval defined for the <ExitEventThresholdTime> parameter elapses and does not generate an event.

<EventCollectControlTime>

To define <EventCollectControlTime>, enter the time (an int value), in milliseconds, for a device to complete a reading cycle for the tags of a pallet or container before starting a new reading cycle. When this time elapses, the reading cycle concludes (that is, the device has read all of the new tags) and the Pallet Shelf Filter then generates an event.

3.3.1 Creating a Filter Instance

To create a filter instance:

1. Within the <DeviceGroups>, locate the <Device> to which to add the filter instance.

2. Add a <FilterInst> element to the device's <FilterInsts> section.

3. For the <Extension> element, specify the name of the filter for the class attribute, and the id of the filter for the reference attribute.

4. Set the <ParameterInsts> to match the attribute values set for the filter's <Parameters> element.

5. Save edgeserver.xml and then restart the Oracle Sensor Edge Server. For more information on starting and stopping the Oracle Sensor Edge Server, refer to Section 1.3.

   
   

   Note: You define device-level filters using the <FilterInsts> tag of the <Device> element. You define device group-level filters using the <Filterinsts> tag of the <DeviceGroup> element.

   
   

<FilterInsts>
      <FilterInst>
          <Sequence>1</Sequence>
          <FilterName>PalletPassFilter</FilterName>
          <Extension class="Filter" reference="50"/>
          <ParameterInsts>
            <ParameterInst>
              <ParameterMetaData reference="52"/>
              <Value>11</Value>
              <Name>ExitEventThresholdTime</Name>
            </ParameterInst>
            <ParameterInst>
              <ParameterMetaData reference="53"/>
              <Value>12</Value>
              <Name>EventCollectControlTime</Name>
            </ParameterInst>
          </ParameterInsts>
          <NeedReload>false</NeedReload>
          <Name>PalletPassFilter</Name>
        </FilterInst>
 </FilterInsts>