I am pretty new to circuit/PCB design and have noticed something that confuses me. Let's take a logic gate as an example.

In my circuit design software, the schematic symbol for a logic gate has 3 pins: A, B, and Y. But when I look at the datasheet, I see that the actual component has 5 pins: A, B, Y, Vcc, and GND.

Why wouldn't Vcc and GND be included in the schematic? Do I only add those connections once I transfer my schematic to a PCB?

 

Many PCB layout software omit or do not show the power common and power pins, they are noted and processed automatically however when the PCB layout is carried out.
Max.

 

Some simulation and schematic software only show the active pins (or have an option to suppress showing the power and ground) in logic circuits since power and ground are an implied requirement and showing all of them tends to clutter the schematic. But of course they must be connected when the PCB is made.

Edit: It was a dead heat but Max beat me by a nose..