1.TSTOCKPOSITION vs TRESERVATION - > how it is connected?
Answer:
TSTOCKPOSITION = (Stock on hand)
TRESERVATION = (Reservation/Booking)
->this connects through TRESERVATION
TSTOCKPOSITION (Physical Stock)
    ↓
RESERVEDQUANTITY (Increase)
    ↓
TRESERVATION (Reservation Record)

CONNECTION LOGIC:

UPDATE TSTOCKPOSITION
SET RESERVEDQUANTITY = RESERVEDQUANTITY + @Quantity  -- need to reserve in stock
WHERE OUID = @OUId
  AND ITEMID = @ItemId
  AND SKUID = @SKUId
  AND STOREID = @StoreId
  AND (QUANTITY - RESERVEDQUANTITY) >= @Quantity  -- need to check whether the needed stock is there 

2. how the reservation knows the how many stock are ther in position?

-- TSTOCKPOSITION haveing total quantity
SELECT 
    OUID, ITEMID, SKUID, STOREID,
    QUANTITY,                          -- Total physical stock
    RESERVEDQUANTITY,                  -- Already reserved
    (QUANTITY - RESERVEDQUANTITY) AS AVAILABLE  -- Available to reserve
FROM TSTOCKPOSITION
WHERE OUID = -1 AND ITEMID = -1 AND SKUID = -1 AND STOREID = -1;

Result:

QUANTITY = 8.0000 (Total)
RESERVEDQUANTITY = 8.0000 (Already booked)
AVAILABLE = 0.0000 (Nothing left to book)

3.Is Position table parent ?

No! Neither is parent. They are related but independent tables:

TSTOCKPOSITION (Stock Position)
    ↓ (update)
TRESERVATION (Reservation)

Not Parent-Child, but Reference relationship

Relationship:
TSTOCKPOSITION = Tracks physical stock (how many items physically exist)
TRESERVATION = Tracks commitments (how many are promised to customers)

Think of it like:
TSTOCKPOSITION = Bank Account Balance (8,000 rupees)
TRESERVATION = Cheques issued (2,000 rupees issued)
Available = 8,000 - 2,000 = 6,000 rupees left

4. Is Reservation table final stock ? or Is Position table final stock a?

Position table is the source of truth for physical stock.
TSTOCKPOSITION = Real physical stock (8 items in warehouse)
TRESERVATION = Only shows booked items (2 items booked)

Flow:

1.Physical stock enters → TSTOCKPOSITION

2.Customer orders → TRESERVATION (book from stock)

3.Stock decreases in TSTOCKPOSITION (RESERVEDQUANTITY increases)

4.When delivered → ISSUEDQUANTITY increases in TRESERVATION

Final stock is TSTOCKPOSITION:

Available Stock = QUANTITY - RESERVEDQUANTITY

┌─────────────────────────────────────────────────────────┐
│                   STOCK SOURCE FLOW                     │
├─────────────────────────────────────────────────────────┤
│                                                         │
│  1. TSTOCKPOSITION (Physical Stock)                    │
│     ┌──────────────────────────────────────────┐       │
│     │ OUID=-1, ITEMID=-1, SKUID=-1, STOREID=-1│       │
│     │ QUANTITY = 8.0000                         │       │
│     │ RESERVEDQUANTITY = 0.0000                 │       │
│     └──────────────────────────────────────────┘       │
│                    ↓                                    │
│  2. User Requests Reservation                          │
│     ReservedQuantity = 2.0000                         │
│                    ↓                                    │
│  3. Check Availability                                 │
│     (QUANTITY - RESERVEDQUANTITY) >= 2.0000          │
│     (8 - 0) >= 2                                    │
│                    ↓                                    │
│  4. UPDATE TSTOCKPOSITION                             │
│     RESERVEDQUANTITY = 0 + 2 = 2.0000                │
│                    ↓                                    │
│  5. INSERT TRESERVATION                               │
│     STOCKRESERVATIONID = 10                          │
│     RESERVEDQUANTITY = 2.0000                        │
│                    ↓                                    │
│  Final State:                                         │
│  TSTOCKPOSITION: QUANTITY=8, RESERVED=2, AVAILABLE=6  │
│  TRESERVATION: RESERVED=2, ISSUED=0                  │
└─────────────────────────────────────────────────────────┘