Addition by Subtraction by Addition (ASA) refers to modifying URLs to access information not normally accessible. ASA involves analyzing URL patterns to determine what can be added or subtracted to uncover new content. As an example, the document demonstrates how changing the year in a sports stats URL from 2009 to 2005 using ASA retrieves the stats for the 2005 season. The document encourages experimenting with adding or subtracting terms like "resume" or "bio" from URLs to discover hidden information on websites.

1. Addition by Subtraction by Addition (ASA)
ASA refers to the skill of adding to, or subtracting from a URL to gain access to
things that are not normally accessible by the normal URL. ASA is all about
patterns, what patters are used in the URL, and what do these patterns tell us, and
what can be substituted to find something not normally found. ASA is basically
reverse peeling. As we learned in an earlier blog, peeling is taking away from a
URL to uncover information. ASA is not just taking away, but adding to a URL,
substituting in a URL to uncover new things. For the purposes of an explanation I
am going to use a sports site called CBS Sportsline. Within CBS Sportsline you
can access a lot of information. Specifically you can see players stats during a
particular season. Who was the league leaders during a particular regular season.
However not every season is available. But if you look at the URL of the most
resent season they have available, you will notice a pattern. The URL has within it
4 characters of the URL that represent the year of that season. . So if you are
looking at stats for the 2009 season, and want the stats of the 2005 season, all you
should need to do is change 4 characters to show 2005 and hit enter and there you
go the 2005 stats. (see below example)
http://www.cbssports.com/nfl/stats/leaders/NFL/PYDS/2009/regular
The hyperlink above shows the regular season stats for 2009, now the site does not
show the regular season stats for 2005, but a simple change to the URL, changing
the year from 2009 to 2005 (see below), and presto you have the stats for 2005.
http://www.cbssports.com/nfl/stats/leaders/NFL/PYDS/2005/regular

2. Now you will notice the hyperlink says at the end regular. This means regular
season. Guess what would happen if you changed the word regular to post for
postseason (playoffs) or to pre for preseason. You are right you will get the post
season or pre season stats
This same premise can work for us as Sourcers. If you are looking at a site,
examine the URL, see what happens if you add things like; resume, bio, CV etc.,
or when you take part of it off, and add things like; resume, bio, CV etc.. You
might be surprised at what you find. I did this once and it was pretty amazing what
I found. I was looking at a particular company’s website (company name withheld)
and decided to take off part of the URL and input different things. Low and behold
next thing I know I had access to the bio of every person who worked at the
company. Now obviously I have utilized this method a lot, and was only
referencing this one time as an example. If you examine the URL right, though you
will figure out what words will work to get what you want. Like with anything
practice makes perfect, and sometimes examining the primary URL and any
connected URLs can help give you an idea of what words will work. As you are
using boolean searches (see past blog posts on sourcing and boolean search strings)
to find resumes, notice what words the URLs have in them and how they are used,
how they are formed, and soon you will become an expert in ASA.