As mentioned, you can't really do that with \unidirectionalassociation the way it is defined. It might be possible to redefine, but I think drawing those arrows using TikZ-macros instead is just as well. There will be several ways of doing this, I'll explain one here.
In the code below, the first thing I do, after the classes, is
\draw [umlcd style] (Factory.north) -- ++(0,2cm)
coordinate (tmp)
node[right,midway] {creates};
This draws a line using a style defined by pgf-umlcd, starting at the top of the Factory class, and ending 2cm higher. The ++ indicates that the coordinate, (0,2cm), is relative to the previous coordinate. Then I define a coordinate at that endpoint called tmp, which is used later.
I also add a node (used to place text) halfway along the line (that's what midway means), on the right side of it. If you don't want the word creates next to this line, remove node[right,midway] {creates}. (But don't remove the semicolon, that is required to end the path.)
Then I draw three lines starting at the tmp coordinate defined above, to each of the product classes:
\foreach \endpoint in {ProductA,ProductB,ProductC}
\draw [umlcd style,fill=none,->] (tmp) -| (\endpoint.south)
node[pos=0.75,right] {creates};
I used a loop here, you could also have three separate \draw statements. For these lines, I add fill=none,-> in addition to umlcd style. The first is needed because the style sets a fill colour, so filling must be disabled. The latter is needed to activate the arrow tip at the end of the lines.
The syntax (a) -| (b) means that instead of drawing a straight line, TikZ draws first horizontally from the point a, and then vertically up to b.
Again I add a node, and again, remove it if you don't want it. The pos=0.75 normally means that it should be placed at the point that is 75% of the way from a to b. For paths using -| (or |-) however, pos=0.5 is always at the corner, so pos=0.75 is halfway between the corner and the end of the path.
Output and complete code below.
\documentclass[border=5mm]{standalone}
\usepackage{pgf-umlcd}
\begin{document}
\begin{tikzpicture}
\begin{class}{Factory}{0,0}
\attribute{}
\attribute{}
\operation{}
\operation{}
\end{class}
\begin{class}{ProductA}{4,5}
\attribute{}
\attribute{}
\operation{}
\operation{}
\end{class}
\begin{class}{ProductB}{-2,5}
\attribute{}
\attribute{}
\operation{}
\operation{}
\end{class}
\begin{class}{ProductC}{-8,5}
\attribute{}
\attribute{}
\operation{}
\operation{}
\end{class}
\draw [umlcd style] (Factory.north) -- ++(0,2cm)
coordinate (tmp)
node[right,midway] {creates};
\foreach \endpoint in {ProductA,ProductB,ProductC}
\draw [umlcd style,fill=none,->] (tmp) -| (\endpoint.south)
node[pos=0.75,right] {creates};
\end{tikzpicture}
\end{document}
pgf-umlcd(not that it matters much, it's all TikZ anyway). A couple of examples I found: https://tex.stackexchange.com/questions/178603/ https://tex.stackexchange.com/questions/50780/ https://tex.stackexchange.com/questions/280521/ If you're unable to figure it out, add a complete code example to your question with what you've tried, and someone will surely be able to fill in the blanks. – Torbjørn T. Oct 17 '17 at 18:02\unidirectionalassociationto one source to one target. But here is one source to multiple target. I edited my question. – alhelal Oct 18 '17 at 10:07\unidirectionalassociationonly draws a single straight line. That's it. You can still do what you ask for, but you'll need to use something else. But please post code, I don't feel like making up an example only to have to redo it three times afterwards because I didn't fully understand what you were after in the first place. – Torbjørn T. Oct 18 '17 at 10:15