Forum OpenACS Development: Re: XML to XoTCL Object

Do you say that you have implemented an XML Schema validator? That sounds like a useful contribution! Can you explain more?

I'm not sure of the terminology. This code is all part of a type system which is relatively independent from the tWSDL/TWiST code. The type code can create types using the methods of restriction outlined in XML-Schema datatypes:

http://www.w3.org/TR/xmlschema-2/

and these can be combined into complexTypes, mostly limited to sequences:

http://www.w3.org/TR/xmlschema-1/

Once the types are defined, then instances can be created with the ::new proc (which supports full nesting to any depth).

The defined schema is part of the WSDL file, but could probably be pulled out as an independent document. Documents/instances can be validated using the ::validate proc. The validation does structural validation then type validation. Validation stops on the first error and backs out, marking a path (using internal variables). Right now the only use for this validation information is to create a SOAP fault indicating the reason for failure, but maybe you could go in and correct something and revalidate.

The best way to understand all of this is to just look at the auto-generated code for handling all of this:

http://junom.com/ws/mywebservice/

The entire auto-generated code is based upon the config:

http://junom.com/ws/mywebservice/index.txt

The auto-generated WSDL/schema:

http://junom.com/ws/mywebservice/?WSDL

The derivation of decimal types is complex to code, but very useful. The example operation is at:

http://junom.com/ws/mywebservice/?op=TestDecimalValueOperation&mode=display

The generated type validation procedure is here:

http://junom.com/ws/mywebservice/?ns=::wsdb::types::mywebservice::TestDecimal

In general, you can browse under either simpleTypes or complexTypes to see the various code for either type creation or type validation.

What is wrong about using appendFromList?

There is nothing wrong with it, however it would mean several inconveniences. The first is it would require tDOM. Second, during building the document, additional information is added which aids validation (see above examples). Also, invalid documents are marked with additional metadata which isn't part of the XML document. Another problem is that you can't easily introspect the document to figure out why you can't get something to work. I use a namespace browser to inspect documents and all code generated by the service description. Tracking down data errors in tDOM would be difficult (for me at least). Also, some documents are constructed in parts. This means they need to be created before their parents, even before the document. This is easy, since the creating proc only needs to return the location (namespace) of the new element. This name can be used as a reference to add the element.

So documents/elements are sometimes looked over more than once. One additional example is the problem of serialization. I'm using only document/literal, so there is minimum need to worry about it, but rpc/(encoded/literal) are only slightly different from document/literal. In many cases, only a type attribute needs to be added to elements. Since the SOAP layer is above the document creation layer, this decision cannot be made until after the document is filled with data. Some future RPC layer could use the schema and go back and add the type information, possibly adding prefixes, etc.

There are example Tcl reps of XML documents under the ::xml::instance namespace:

http://junom.com/ws/mywebservice/?ns=::xml::instance

Finally, there is nothing wrong with tDOM, I would never suggest that, but you can't get any better introspection than simply browsing the document. This type of introspection is aimed at finding errors and understanding what is going on. Point and click is easier on my brain.

Gustaf,

From the user's perspective, the xml component of tWSDL does document validation based upon a defined XML Schema. However, there is more going on, and there is not a single step which qualifies quite by this definition.

First, types are defined via a Tcl API and the XML Schema is generated based upon the definitions. If this were not the case, then all the xsd types would have to be hand coded, or would they not even exist until you parsed an xsd which defined them? The link below shows how the xsd types are derived:

http://junom.com/gitweb/gitweb.perl?p=twsdl.git;a=blob;f=packages/wsdl/ns/ns-xsd.tcl

The page needs some cleanup, but basically it outlines how the internal API generate the type system. I'll include a few lines here:

# Create xsd schema
::wsdl::schema::new xsd "http://www.w3.org/2001/XMLSchema"

# anySimpleType
::wsdl::types::primitiveType::new xsd anySimpleType {return 1} 

# string
::wsdl::types::primitiveType::new xsd string {return 1} 

# dateTime
::wsdl::types::primitiveType::new xsd dateTime "return \[::wsdb::types::tcl::dateTime::toArray \$value\]" 

# duration
::wsdl::types::primitiveType::new xsd duration "return \[::wsdb::types::tcl::dateTime::durationToArray \$value\]" 

# boolean
::wsdl::types::simpleType::restrictByEnumeration xsd boolean xsd::string {0 1 true false}

# Decimal Type
::wsdl::types::simpleType::restrictDecimal xsd decimal xsd::string {pattern {\A(?:([\-+]?)([0-9]*)(?:([\.]?)|([\.])([0-9]+))){1}\Z}}

::wsdl::types::simpleType::restrictDecimal xsd integer tcl::integer {fractionDigits 0}
::wsdl::types::simpleType::restrictDecimal xsd int tcl::integer {fractionDigits 0} 
::wsdl::types::simpleType::restrictDecimal xsd nonPositiveInteger xsd::integer {maxInclusive 0}
::wsdl::types::simpleType::restrictDecimal xsd negativeInteger  xsd::integer {maxInclusive -1}
::wsdl::types::simpleType::restrictDecimal xsd short xsd::integer {minInclusive -32767 maxInclusive 32767}
::wsdl::types::simpleType::restrictDecimal xsd byte xsd::integer {minInclusive -127 maxInclusive 127}

Structural types are supported as sequences. You can specify minOccurs, maxOccurs, type, default value, nillable, and implicitly, the order of child elements. Children can be either simpleType content or another complexType. You can also have a child element with a local name which refers to a global type. The code for creating and validating the type is in the global type, but the local element provides the name and reference to the global type.

The structural details are checked first during validation. If all children are present in the correct number, validation steps through the child elements until eventually children with only simpleType content are validated.

If there is a validation error, the validation checker marks the 'nodes' on the way back out so a client can get a complete path to the error and a pretty good error message indicating what failed. In tWSDL, this is used to return a SOAP fault message (client fault). However, any application could easily access the same information. The error information is stored with the document rep, but it isn't part of any serialized version of the document (at least with XML).