[xsd-users] NoEntry exception from FrontendElements::Context

[Ray Lischner]

The exception is thrown from code I added to Code Synthesis, and I am trying to understand the circumstances in which the problem arises.

The schema is as follows:

<schema xmlns=http://www.w3.org/2001/XMLSchema>
 <complexType name="T">
  <sequence>
   <choice>
    <sequence>
     <element name="a" type="int"/>
     <element name="b" type="int"/>
    </sequence>
    <sequence>
      <element name="b" type="int"/>
    </sequence>
   </choice>
 </sequence>
</schema>

The schema is simplified from the real schema and seems to be the minimum needed to manifest the problem, which is that when traversing the semantic graph in xsd/cxx/tree/tree-header.cxx, I dispatch to a new class:

struct MyClass : Traversal::Element, // several other Traversal classes
{
  Void traverse (SemanticGraph::Element& e) {
    if (min (e) == 0) // throws FrontendElements::NoEntry when traversing the second "b" element
      do_something();
  }
};

If I change the name of the second "b" element to "c", the problem goes away and every element has a min and max. If I change the name of the first "b" to "c", the problem goes away.

I know this example schema can be rewritten without the <choice>, but the real schema from this is derived cannot. The branches of the <choice> are more complicated.

So my question is, in what circumstances does an element lack a "min" or "max" in its context? And what should I do about it?


Ray Lischner,
Distinguished Member of Technical Staff
133 National Business Pkwy, Ste 150     t. 443.539.3448
Annapolis Junction, MD 20701            c. 410.854.9787
rlischner at proteuseng.com                f. 443.539.3370