Exercise 2: Why COMP-3 and PIC Aren't the Same Kind of Thing — Possible Solution ==================================================================== The colleague's claim treats PICTURE and USAGE as if they answer the same question about a field, but this chapter's own real material shows they answer two genuinely different questions entirely. WHAT A PICTURE CLAUSE ACTUALLY DESCRIBES This chapter describes the PICTURE clause as defining a field's own logical shape - how many digits it holds, whether it's numeric, alphabetic, or alphanumeric, where an implied decimal point falls, and whether it's signed. A PICTURE clause answers the question "what kind of value, and what shape, does this field logically represent?" - it says nothing at all about how those bytes are actually arranged in real physical storage. WHAT A USAGE CLAUSE (LIKE COMP-3) ACTUALLY DESCRIBES This chapter describes USAGE as controlling a field's real, physical storage format - separate from what its PICTURE clause describes. COMP-3 specifically means the value is stored as packed binary-coded decimal, real, physically packing two digits into each byte rather than using one byte per digit. USAGE answers a completely different question: "how are these logical digits actually laid out in memory or on disk?" WHY BOTH CAN APPLY TO THE SAME FIELD AT ONCE This chapter's own worked example shows both clauses being used together on the very same field: WS-BALANCE is declared as PIC S9(7)V99 COMP-3 - the PICTURE clause (S9(7)V99) describes its logical shape (a signed 7-digit number with 2 implied decimal places), while the USAGE clause (COMP-3) separately describes how those same digits are physically packed into storage. If PICTURE and USAGE described the same thing, combining them on one field wouldn't make sense - but they combine precisely because they're describing two independent, complementary aspects of the same field. WHY THIS DISTINCTION MATTERS IN PRACTICE Two fields could share an identical PICTURE clause - the same logical shape - while using entirely different USAGE clauses, meaning they'd represent the same kind of value while being physically stored in completely different ways (one as plain human-readable digits, another as compact packed decimal). This is exactly the real reason this chapter's own table on mainframe storage efficiency exists as a separate topic from the PICTURE symbols table before it. ANSWER: COMP-3 and PIC are not the same kind of thing because they answer two genuinely different questions about a field: a PICTURE clause describes a field's logical shape (how many digits, what type, where the decimal point falls), while a USAGE clause like COMP-3 describes how that same logical value is physically stored (as packed binary-coded decimal, in COMP-3's case). This chapter's own worked example shows both being applied to the same field at once (PIC S9(7)V99 COMP-3), which only makes sense because they describe independent, complementary aspects of that field rather than the same thing twice. WHY THIS WORKS AS AN ANSWER ------------------------------ This distinguishes the specific question each clause answers (logical shape vs. physical storage), and uses the chapter's own worked example combining both on one field as direct evidence that they aren't redundant descriptions of the same property.