WebTree Logic

It's called a "tree" because the selection from looks vaguely like one.

The WebTree Process
Registration—or, more properly, submission of course preferences—has since the mid 1970s used priorities that allow all students a chance at one course before any student has a chance at a second. Within each choice, seniors come first, then juniors, and so on; within each class, a random number establishes the order. (Because all original course selections must be processed together, it is not possible to show whether a class is full at the time you select it. When you make your selections, all classes are empty. They start filling only when the batch program runs to process everyone’s selections.)
The second key is that WebTree allows alternatives for each selection you make rather than forcing you into the situation in which you list eight courses (for instance) without any chance to specify what groupings might go well together.  The program goes through the whole student body to assign one course to each person, then again to assign the second course to each person, and so forth.  On each pass, you have the chance to specify at least one alternative, one either-or.

How It Works

 The registration program looks at the top level of each tree first, and the successful selection determines where the computer goes later for the second and third choices. So: your first-choice course goes in Tree 1, slot #1. Your alternate for that course goes in Tree 2, the top slot = slot #2; your second alternate in the top slot of Tree 3, slot #3. When the program seeks first choices, if you don’t get the course in #1, the program tries #2; if you do get #2, then “Tree 2” will be the source for the program’s next steps. If you get neither “1” nor “2,” the program goes to #3; if you get #3, then "Tree 3" will be the source for the program's next steps. (If you get neither 1, 2, nor 3, the program will go to tree 4, starting at the left.)

Think of it this way: let's say that the most important course for you to get is BIO 111, which is offered at different times.  Your preference is for the one that meets at 9:30 MWF, with a lab on Tuesday afternoon.  That is BIO 111B; you put it first (slot 1, the top of Tree #1).  But if it's full, you'd like to get the BIO 111 that meets at 8:30 MWF with its lab on Thursday afternoon.  That's BIO111D; you put it in slot #2 (the top of Tree 2).  If you don't get either,  you want the BIO 111 that meets at 8:30 MWF and has its lab at 8:30 on Thursday mornings; that's BIO 111C, so you put it in slot #3 (the top of Tree 3).  If luck is really against you and you get none of the three, you might even put another section -- class at 11:30 MWF, lab at 1:30 on Wednesdays, BIO 111E in 4A.  The same principle applies if you want not BIO 111B or D or C or E, but you want some W-course as your first choice, and you have alternates to it; or you have any other list of alternates for your first-choice course.

Confused yet?   We really recommend using the "Web Tree Visual" guide and remembering where "and" and "or" can occur: you get 1 OR 2 OR 3, but 1 AND (1A OR 1B) -- and the same principle on down through 1AA, etc.  Tree 4, remember, is different: it's the supply for the fourth course, certainly, but also for any time the program runs out of options.

 On the second pass: if you’ve been assigned to your first choice—#1—the program will try to assign 1A; if it can’t, the program will try 1B. If neither 1A nor 1B is available, the program goes to Tree 4, which is where the program turns whenever it hits a dead end. (Remember that what you get first determines which tree the program uses for the next steps.  If you got course #2 or course #3, the program will try 2A and 2B, or 3A and 3B, as appropriate.  There's one exception: if your first course comes from Tree 4, on the second pass, the program will come back to tree 1 and attempt 1A, then 1B.)

Going back to the earlier  first-choice BIO examples: if you get choice #1 (BIO 111B), the next time the program comes back to you it will know that you have a class at 9:30 MWF and that your Tuesday afternoon is committed to a Biology lab.  The course you have in 1A (with an alternate in 1B) is one you selected to go along with the Biology at those hours: let's say either German 101A (12:30 MWF) or Russian 101 (also 12:30 MWF).  Put those courses at 1A and 1B.  If the program doesn't assign the German (in slot 1A), it will try the Russian (in Slot 1B).  Since those times also fit with your #2 -- BIO 111D, which you hoped to get if 111B was full -- you may use those same choices for 2A and 2B.

On the third pass: if you’ve been assigned, for example, your #2 and #2B, the program will look at 2B.A, then at 2B.B. If neither is successful, the program goes to tree 4.  (If you got #1 and #1A, the program will attempt 1A.A, then 1A.B.  Remember: once you start on a branch of the tree, the program stays in that branch -- using Tree 4 as the last resort whenever it hits a dead end.)

On the fourth pass, the program starts with anything left in tree 4. If unsuccessful in giving you a course from that line, it will look at the whole form and assign you to any course listed for which there’s no time conflict and which hasn’t yet been assigned. NOTE:  The WebTree program won’t give you two different sections of the same course. It also will process only the courses and sections you list: if, for instance, you don't get the section of MAT 130 you wanted, the program will not put you in a different section unless you have listed that section as a possibility.