Forum OpenACS Development: Re: XML to XoTCL Object

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12: Re: XML to XoTCL Object (response to 10)
Posted by Gustaf Neumann on
me:
Do you say that you have implemented an XML Schema validator?

Tom:

I'm not sure of the terminology.

An XML Schema validator is a program that accepts an XML Schema (as defined by w3c) and a schema instance (an XML document), analyzes both and determines if the XML document is a valid instance of the schema (well-formed by XML rules and obeying the structural and datatypes constraints by the XML Schema).

If i understand correctly, your implementation parses the XML-schema (from the WDSL document) into the namespace-structure and auto-generates the type-checkers for the primitive and derived XML datatypes (terminology of http://www.w3.org/TR/xmlschema-2/).

Does your implementation cover the full set of built-in datatypes of XML Schema, the full set of built-in derived datatypes, and the full set of simple type definitions (section 4)? I understand, that you have not implementd complex type checking (yet).

This is certainly an interesting addition to a tcl based xml processing environment, complementing tdom.

Concerning introspection: The term introspection is used in computer science for the ability of a program to query at runtime its own structure and behavior (and optionally to modify it; using terms "read introspection" and "write introspection"). Another term for this is "reflection". This ability is particular important for dynamic languages, where the structures (e.g. object-class relationships, class-class relationships, adding methods or variables dynamically, ...) might change during runtime. By this meaning of the term, tdom has read and write introspection; i would call you usage of the term rather xml structure browsing.

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13: Re: XML to XoTCL Object (response to 12)
Posted by Tom Jackson on

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).