TAILIEUCHUNG - Oracle Built−in Packages- P6

Oracle Built−in Packages- P6: Ah, for the good old days of Version of PL /SQL! Life was so simple then. No stored procedures or functions and certainly no packages. You had your set of built−in functions, like SUBSTR and TO_DATE. You had the IF statement and various kinds of loops. With these tools at hand, you built your batch−processing scripts for execution in SQL*Plus, and you coded your triggers in SQL*Forms , and you went home at night content with a good day's work done. | Appendix A What s on the Companion Disk PROCEDURE capture IS BEGIN last_timing END PROCEDURE show_elapsed IS BEGIN - last_timing END END tmr The program is a function from the built-in package DBMS_UTILITY which returns the number of hundredths of seconds that have elapsed since an arbitrary point in time. DBMS_OUTPUT is another built-in package its PUT_LINE procedure displays output from a PL SQL program to your screen. Notice that there is another code element defined inside the package body besides the capture and show_elapsed procedures the last_timing variable. This variable holds the timing value from the last call to . Since last_timing does not appear in the package specification an external program . one that is not defined in this package cannot directly reference that variable. This restriction is illustrated in the Booch diagram 2 Figure . 2 This diagram is named after Grady Booch who pioneered many of the ideas of the package particularly in the context of object-oriented design. Figure Booch diagram of tmr package So if I try to access the last_timing variable from outside the tmr package I get an error. This is shown as follows SQL exec 100 begin 100 end ERROR at line 1 ORA-06550 line 1 column 14 PLS-00302 component LAST_TIMING must be declared Why should you or anyone else care about where you define the last_timing variable Because it illustrates a critical aspect of a package s value integrity. If I had placed the variable in the specification then a user of the package could write over the value of last_timing and completely invalidate the integrity of the package. Suppose my package specification looked like this PACKAGE tmr IS last_timing NUMBER PROCEDURE capture PROCEDURE show_elapsed Controlling Access with Packages 16 Appendix A What s on the Companion Disk END tmr The package compiles and seems .

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