The Spark sound engine uses five types:
 

spark_Sample	Spark sample type
spark_Preset	Spark preset type
spark_Source	Spark sound source type
spark_Listener	Spark listener type
smpload_SampleInfo	Spark sample information type

The dependency-tree of the types is shown on the picture below:

A  sample can be played even if no source is associated with it. However, sound source features (position, velocity, etc.) are not available in this case.