Using BPEL to Build Composite Services and Business Processes - Oracle SOA Suite 11g R1 Developer's Guide - page 145

Assigning values to variables
In our previous step, we created the variable QuoteInput , which we pass to our
invocation of GetSingleQuote . However, we have yet to initialize the variable or
assign any value to it.
To do this, BPEL provides the <assign> activity, which is used to update the values
of variables with new data. The <assign> activity typically consists of one or more
copy operations. Each copy consists of a target variable, that is, the variable that you
wish to assign a value to and a source (this can either be another variable or an
XPath expression).
For our purposes, we want to assign the stock symbol passed into our BPEL process
to our QuoteInput variable.
To do this, drag an Assign activity from the Component Palette on to your BPEL
process at the point just before our Invoke activity. Then double-click on it to open
up the Assign configuration window. Click on the green plus sign and select
Copy Operation… .
This will present us with the Create Copy Operation window, as shown in the
following screenshot:
On the left-hand side, we specify the From variable (that is, the source). Here we
want to specify the stock symbol passed in as part of the input variable to the
BPEL process. So expand the inputVariable tree, and select /ns2:getQuote/ns2:
stockSymbol .