XML schema invalid

[lexknuther]

The XML schema is currently invalid W.R.T. to the link element. The link uses an xs:all element with some unbounded elements. The XML standard only allows zero or one for the bounds. I'd recommend changing it to a sequence. Changing this would trade off correctness for possible invalidating some existing URDFs.

[dljsjr]

I'm also encountering this issue. I would like to use the standard xjc tooling that comes with JAXB to generate some Java classes for parsing URDF, and the xjc compiler errors out on the "unbounded" value on maxOccurs for link visuals and collisions.

[scpeters]

So the link allows an arbitrary number of collision and visual tags. If we change it to a sequence, I wonder if each type of tag have to be adjacent or can they be mixed? Reading...

[dljsjr]

@lexknuther You seem to know a bit more about XML than I do, what about using choice instead of sequence? Something like this:

  <!-- link node type -->
  <xs:complexType name="link">
    <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="inertial"
                  type="inertial" minOccurs="0" maxOccurs="1" />
      <xs:element name="visual"
                  type="visual" minOccurs="0" maxOccurs="unbounded" />
      <xs:element name="collision"
                  type="collision" minOccurs="0" maxOccurs="unbounded" />
    </xs:choice>
    <xs:attribute name="name" type="xs:string" use="required" />

    <!-- FIXME: undocumented but used by PR2 -->
    <xs:attribute name="type" type="xs:string" />
  </xs:complexType>

[scpeters]

Oh, maybe the sequence could contain both collision and visual definitions...

[scpeters]

Ok, I don't know what I'm talking about at all.

[dljsjr]

@scpeters From my limited understanding, an xs:all doesn't enforce an ordering whereas a xs:sequence does. An xs:choice with an unbounded maxOccurs lets the choice show up as many times as you want and you can have additional bound constraints on the possible choices but in the case of code generators it can generate code that isn't type-safe.

For validation purposes, though, I think it should work.

[scpeters]

Could the inertial tag remain in an xs:all block?

[dljsjr]

xs:complexType can only have a single child element.

[scpeters]

choice seems like the right thing to me

[dljsjr]

Using a sequence of choices might make things look nicer for code generators. I'm going to keep playing with it.

[dljsjr]

The plot thickens.

@scpeters Okay so, apparently, using unbounded in the xs:all is actually valid in XSD 1.1…

It's just that almost nothing out in the wild supports XSD 1.1.