Error compiling w3c schemas with xmerl - erlang

Question

I was trying to get XForms going on my Ubuntu desktop. There does not
appear to be much activity on XForms at the moment and I was trying to
get Backplanejs running. It did not work, and upon examining the javascript
I found it relied Microsoft libraries and activex.
Rather than learn javascript I decided to continue my erlang education and
struggled with xmerl instead. I created a directory for schemas with an
index file. The contents of this directory is:
tony#blessing:~/workspace/myXformProject$ ls schemas
SchemaList.txt XForms-Schema.xsd xhtml-lat1.ent xml-events.xsd
SchemaList.txt~ xhtml1-strict.dtd xhtml-special.ent
These schema's have been downloaded from w3c. However these schemas would
not compile yielding the error wfc_PEs_In_Internal_Subset. I would have
expected these well established w3c schemas to compile with xmerl.
What am I doing wrong?
Tony Wallace
6> B.
[{"http://www.w3.org/1999/xhtml",
"schemas/xhtml1-strict.dtd"},
{"http://www.w3.org/2001/xml-events",
"schemas/xml-events.xsd"},
{"http://www.w3.org/2002/xforms",
"schemas/XForms-Schema.xsd"}]
9> {ok,S1} = xmerl_xsd:process_schemas(B).
3450- fatal: {error,{wfc_PEs_In_Internal_Subset}}
** exception exit: {fatal,{{error,{wfc_PEs_In_Internal_Subset}},
{file,"schemas/xhtml1-strict.dtd"},
{line,628},
{col,89}}}
in function xmerl_scan:fatal/2
in call from xmerl_scan:scan_entity/2
in call from xmerl_scan:scan_markup_decl/2
in call from xmerl_scan:scan_ext_subset/2
in call from xmerl_scan:scan_document/2
in call from xmerl_scan:file/2
in call from xmerl_xsd:process_schemas/2
The 3450 refers to the code line in xmerl_scan:
scan_entity_value("%" ++ _T,S=#xmerl_scanner{environment=prolog},_,_,_,_,_) ->
?fatal({error,{wfc_PEs_In_Internal_Subset}},S);
And the error appears to be associated with line 628 of xhtml1-strict.dtd
The column of 89 would appear suspect as line 628 is not that wide:
621 <!--
622 param is used to supply a named property value.
623 In XML it would seem natural to follow RDF and support an
624 abbreviated syntax where the param elements are replaced
625 by attribute value pairs on the object start tag.
626 -->
627 <!ELEMENT param EMPTY>
628 <!ATTLIST param
629 id ID #IMPLIED
630 name CDATA #IMPLIED
631 value CDATA #IMPLIED
632 valuetype (data|ref|object) "data"
633 type %ContentType; #IMPLIED
634 >
635
If you got this far down the post, many thanks!
Tony

Answer 1

You seem to be invoking xmerl_xsd:process_schemas on a collection of schema documents some of which are XSD schema documents and one of which is not an XSD schema document at all, but a document type definition file (xhtml1-strict.dtd). The process_schemas function expects XSD schema documents, which are XML document instances, but DTD files are not XML document instances. You will need to acquire an XSD schema for XHTML, not the DTD, if you want to do what you appear to want to do. Unfortunately, the XHTML WG's XSD schema documents are not the easiest things in the world to use; good luck.
If you want to work with XForms, you might find it easier to get XSLTForms or Orbeon or BetterForms or EMC Formula working than you did to get backplane.js to work.