Issue - 2 - attribute versus element based subfunction invocations

["Yaron Goland" <ygoland@bea.com>]

Chris's mail brings up the issue of - should subfunctions (or subprocesses
as he calls them) be invoked using attributes or XML elements?

An attribution invocation would look something like "<scope
procedure="func(arg1, arg2, arg3)/>".

An XML element invocation would look something like:
<function functionName="func">
   <parameters>
      <parameter.../>
      <parameter.../>
      <parameter.../>
   </parameters>
</function>

I believe that subfunction invocations should be expressed as XML elements
for the same reason that the from and to XML elements in assign activities
are XML elements. Put another way, we should only be willing to have
subfunctions called using attributes if we are willing to throw away from
and to XML elements and replace them with attributes.

I think an example may help to illustrate the problem.

Imagine a function is to be called and passed in a static piece of XML such
as
"<poID><companyDiv><subdiv>32</subdiv><maindiv>14</maindiv></companyDiv><id>
14</id></poID>".

If the only way to call subfunction is via attributes then what the
programmer would have to do is specify:

<scope
procedure="func(&lt;poID>&lt;companyDiv>&lt;subdiv>32&lt;/subdiv>&lt;maindiv
>14&lt;/maindiv>&lt;/companyDiv>&lt;id>14&lt;/id>&lt;/poID>)"/>

I think we can all agree that the previous is unreadable and a nightmare to
type in. Realistically speaking I suspect the only reasonable way to pass in
a static value is something like:

<assign>
   <copy>
      <from>
         <poID>
            <companyDiv>
               <subdiv>32</subdiv>
               <maindiv>14</maindiv>
            </companyDiv>
            <id>14</id>
         </poID>
      </from>
      <to variable="dummyVariable"/>
   </copy>
</assign>
<scope procedure="func(dummyVariable)"/>

In other words, the programmer has to create a dummy variable, do a full
assign and then copy the dummy variable in. I believe it is both easier and
less error prone to take our lead from the "from" XML element used in
assigns and specify:

<function functionName="func">
   <parameters>
      <parameter>
         <poID>
            <companyDiv>
               <subdiv>32</subdiv>
               <maindiv>14</maindiv>
            </companyDiv>
            <id>14</id>
         </poID>
      </parameter>
   </parameters>
</function>

In fact we can use almost all of the 'from' syntaxes as parameter types on
the XML form of the function call. This will make the function call very
natural to a BPEL programmer. This also makes other common scenarios very
simple. For example, let us say that a function takes a string as an
argument and that string is in a message, in part P2 in an element
identified by the XPATH "/foo/bar/blah". The function call would look like:

<function functionName="func">
   <parameters><parameter variable="Message" part="p2"
query="/foo/bar/blah"/></parameters>
</function>