### choiceSource

This type of seismogram source allows for a choice to be made between several seismogram sources based on characteristics of an event and channel. It goes through each of the choices in order, and if the subsetter inside of a choice matches, it uses it. If no choice matches, the seismogram source in the otherwise is used. The example gets data from the POND from half a year ago up until 8 weeks ago. For anything more recent, it gets data from the BUD. Other uses for this are to switch seismogram sources based on the preferred seismogram sources for a station, or to use the POND (IRIS_PondDataCenter) to retrieve data if an event meets the POND criteria but use the IRIS mass store (IRIS_DataCenter) otherwise.

### Example

    <choiceSource>
        <choice>
            <originTimeRange>
                <startTime>
                    <earlier>
    <timeInterval>
      <value>26</value>
      <unit>WEEK</unit>
    </timeInterval>
                    </earlier>
                </startTime>
                <endTime>
                    <earlier>
    <timeInterval>
      <value>8</value>
      <unit>WEEK</unit>
    </timeInterval>
                    </earlier>
                </endTime>
            </originTimeRange>
            <fdsnDataSelect>
                <name>Local Caching server</name>
                <host>myserver.myuniversity.edu</host>
            </fdsnDataSelect>
        </choice>
        <otherwise>
            <fdsnDataSelect>
                <name>IRIS Server</name>
            </fdsnDataSelect>
        </otherwise>
    </choiceSource>

### This consists of

<choiceSource>

<choice> At least once
eventChannelPlus
seismogramSource
</choice>
<otherwise>
seismogramSource
</otherwise>
</choiceSource>

### Places this can be found

In seismogramSource there is a choice between all of the following

- fdsnDataSelect
- choiceSource
- tryInOrder
- winstonWaveServer
- fixedDataCenter