Data Conversion - Information Systems Reengineering, Integration and Normalization - page 145

Fig. 4.5 A sample hierarchi-
cal schema

DNO MGR BUDGET

ENO JOB PJNO LEADER

ITEMNO DESC

Its DEFINE statements can be described in the following where for each DEFINE
statement, code is generated to allocate a new subtree in the internal buffer.

GROUP DEPT:
OCCURS FROM 1TIMES;
FOLLOWED BY EOF;
PRECEDED BY HEX '01';
:
ENDEMP;
GROUPPROJ:
OCCURS FROM 0TIMES;
PRECEDED BY HEX'03';

:
ENDPROJ;
ENDDEPT;

For each user-written CONVERT statement, we can produce a customized pro-
gram. Take the DEPT FORM from the above DEFINE statement:

T1 = SELECT (FROM DEPT WHERE BUDGET GT '100');

will produce the following program:

/* PROCESSLOOPFOR T1 */
DO WHILE(notend of file);
CALL GET(DEPT);
IF BUDGET > '100'
THEN CALL BUFFER_SWAP(T1,DEPT);