HP Neoview Release 2.5 Software - Manual (Page 97)

Operator Groups
Each operator is identified in the query tree by an icon that identifies the group type. These are
the operator groups:
File Scan
Root
Exchange
Insert
Split Top
Partition Access
Tuple
ESAM Subset
Group By
Merge Union
Default
ESAM Unique
Join
Sort
Data Mining
The default icon (question mark) is used for operators not represented by a group.
Query Workbench Query Details 97