http://www.upu.int has the format standards for international addresses. Publication 28 at http://usps.com has the U.S. format standards. CASS software like http://semaphorecorp.com validates and standardizes U.S. addresses.
The USPS wants the following unpunctuated address components concatenated on a single line:
* house number
* predirectional (N, SE, etc)
* street
* suffix (AVE, BLVD, etc)
* postdirectional (SW, E, etc)
* unit (APT, STE, etc)
* apartment/suite number
Eg, 102 N MAIN ST SE APT B.
If you keep the entire address line as a single field in your database, input and editing is easy, but searches can be more difficult (eg, in the case SOUTH EAST LANE is the street EAST as in S EAST LN or is it LANE as in SE LANE ST?).
If you keep the address parsed into separate fields, searches for components like street name or apartments become easier, but you have to append everything together for output, you need CASS software to parse correctly, and PO boxes, rural route addresses, and APO/FPO addresses have special parsings.
A physical location with multiple addresses at that location is either a multiunit building, in which case letters/numbers after units like APT and STE designate the address, or it's a Commercial Mail Receiving Agency (eg, UPS store) and a maildrop/private mailbox number is appended (like 100 MAIN ST STE B PMB 102), or it's a business with one USPS delivery point and mail is routed after USPS delivery (which usually requires a separate mailstop field which the company might need but the USPS won't want on the address line).
A contact with more than one physical address is usually a business or person with a street address and a PO box. Note that it's common for each address to have a different ZIP code.
It's quite typical that one business transaction might have a shipping address and a billing address (again, with different ZIP codes). The information I keep for EACH address is:
* name prefix (DR, MS, etc)
* first name and initial
* last name
* name suffix (III, PHD, etc)
* mail stop
* company name
* address (one line only per Pub 28 for USA)
* city
* state/province
* ZIP/postal code
* country
I typically print mail stops somewhere between the person's name and company because the country contains the state/ZIP which contains the city which contains the address which contains the company which contains the mail stop which contains the person. I use CASS software to validate and standardize addresses when entered or edited.