Query Plan Sybase and Tree Datastructure - database

Question

This is regarding the query plan of sybase and how the tree is formed based on the query plan
1)
How this query plan is formed into proper tree?
Starting with emit.Insert is the child of Emit and Restrict is the child of Insert and so on. It doesnt tally with the explanation.
2)May I know how the actual processing takes and how the interim result is flown to achieve the final outcome? and what is the maximum number of child a node can have?
Sorry for such long example.
text delete operator
Another type of query plan where a DML operator can have more than one
child operator is the alter table drop textcol command, where textcol is the name
of a column whose datatype is text, image, or unitext. The following queries and
query plan are an example of the use of the text delete operator:
1> use tempdb
1> create table t1 (c1 int, c2 text, c3 text)
1> set showplan on
1> alter table t1 drop c2
QUERY PLAN FOR STATEMENT 1 (at line 1).
Optimized using the Abstract Plan in the PLAN clause.
5 operator(s) under root
The type of query is ALTER TABLE.
ROOT:EMIT Operator
|INSERT Operator
| The update mode is direct.
|
| |RESTRICT Operator
| |
| | |SCAN Operator
| | | FROM TABLE
| | | t1
| | | Table Scan.
| | | Forward Scan.
| | | Positioning at start of table.
| | | Using I/O Size 2 Kbytes for data pages.
| | | With LRU Buffer Replacement Strategy for data pages.
| |TEXT DELETE Operator
| | The update mode is direct.
| |
| | |SCAN Operator
| | | FROM TABLE
| | | t1
| | | Table Scan.
| | | Forward Scan.
| | | Positioning at start of table.
| | | Using I/O Size 2 Kbytes for data pages.
| | | With LRU Buffer Replacement Strategy for data pages.
| TO TABLE
| #syb__altab
| Using I/O Size 2 Kbytes for data pages.
The below is the explantion
Explanation:
One of the two text columns in t1 is dropped, using the alter table command.
The showplan output looks like a select into query plan because alter table
internally generated a select into query plan. The insert operator calls on its left
child operator, the scan of t1, to read the rows of t1, and builds new rows with
only the c1 and c3 columns inserted into #syb_altab. When all the new rows
have been inserted into #syb_altab, the insert operator calls on its right child,
the text delete operator, to delete the text page chains for the c2 columns that
have been dropped from t1. Post-processing replaces the original pages of t1
with those of #syb_altab to complete the alter table command.