OK. It sounds like you want to start with a continuous line that is one branch, that is, just an ordinary line that is not a branched object. You then want to delete part of the middle of the line, so what you have left is one line object that consists of two branches with a gap between those two branches where the deleted, middle part of the line used to be. Is that correct?
1. Is the part you want to delete a section of the line from one existing vertex to another vertex? or...
2. Is the part you want to delete some section of the line that is not both begun and ended at an existing vertex? If this is the case, how would you indicate what part of the line is to be deleted?
One more question:
How would you do what you want to do either in Arc or in Release 8?
A third way to do this in 9 today:
Suppose we have a line with six vertices: A B C D E F . We want to remove the C D segment, leaving two branches that consist of ABC and DEF.
1. Ctrl-click the line to select it. Ctrl-C to copy it. Shift-ctrl-click the line to deselect it.
2. Shift-Alt-click the line to choose it for editing in the Coordinates tab.
3. Select the A, B and C rows. Delete them. Update the record.
4. Back in the drawing, Ctrl-V to paste the line previously copied.
5. Alt-click that line on the A side to choose it for editing in the Coordinates tab.
6. Select the D, E and F rows. Delete them. Update the record.
You now have two lines that are the ABC and the DEF parts of the original line. Merge them if you like to make one line with two branches.
A fourth way that seems easy to implement: add the ability to double-click into the rightmost cell of a row in the Coordinates tab list to turn on the "new branch" symbol. You could then in one go simply denote new branches at the coordinates where you want first to delete a middle part of the line and then to have the remaining branch left, and then you could just delete the middle branch as I mentioned in my first post.
However, I'm curious as to what the work flow would be for this in other systems, such as Arc. Why invent a new wheel if there is already a good wheel to copy, right?
I'd also be curious to hear what the scenario is for why you would like to do this. It's not something I've seen before so I'm curious if perhaps there is an even better way of going about the ultimate task than looking at the lower level of how this could be implemented.
Aha... a late edit: yet another way to do this with 9 today:
1. Start with your ABCDEF line.
2. Draw two helper lines that intersect that ABCDEF line, one with a vertex in C and one with a vertex on D.
3. Run normalize topology. That breaks the ABCDEF line into branches at the intersections, with one branch being the segment CD.
4. In the normalize topology result, delete the two helper lines.
5. You can now delete the central CD branch as in my first post.
The normalize topology topic shows an illustration with a single long line broken into branches at intersections with other lines.