Originally Posted by Lux Flyer

"Sine" is essentially an identifier indicating a specific individual who is performing the action. I'd say think of it like their signature. Everyone at a location is assigned a unique "Sine" which is two characters long as a combination of numbers 1-9 and letters A-Z (Math wizzes can figure out how many each location can have then). "WEB" is a location identifer used for a sine, and mostly related to automation, but many other locations are also automated. WEB, obviously being something coming from the website. The different sines for web users likely indicate a different application doing the specific action. The other codes like SU, GS, PD, etc. are essentially permission levels which dictate what a specific user's identifier is allowed to do.



Not necessarily true that the airport agent's code will always be the airport code. Mentioned above, there is a limit to the number of unique sines for each location. So some of the larger airports (hubs) or other locations who have more employees needing access than available sines for a single city will also have a pseudo city code. I think when they get this large, they start dividing those with supervisor access to different city codes, so ORD might be standard gate agents whereas CHI might be a supervisor for ORD. That also allows them to ensure everyone still has a unique identifier even when using shared applications like Jet or Aero [they don't necessarily enter their sine anymore, but rather it is attached to their company profile and automatically gets entered through a SSO mechanism).

Also the city codes directory might not necessarily reflect the most current assignments of a code, since the software was from Continental's days. As I understand it, among other interesting city code assignments still in place, there is still one assigned that was originally for Northwest employees working in SHARES.

Edit: To also add, even though some systems may use a "WEB" or "HDQ" or other sine that doesn't identify a specific individual that may just be the agent using a web based interface to do the action. There is a different history section of the PNR (which this viewer apparently doesn't show) that records that data. So even though it might say the "WEB" did this, in the comments the web interface records into the history it will say it was requested by "ABC Q9". This also happens with things like actions you or I might take on the app or website. Instead of the web interface recording a sine (since we don't have one) it would record the MP number that was logged in when the action was done, or possibly a GUID which can identify a specific session and actions that were done during that session if there was no one logged in.