Earlier this year I wrote about hitting some scala limitations:

Scala supports only up to Tuple22.

This means that Scala can define case classes only up to 22 parameters. I've implemented workarounds to use schema that includes complex types that has more than 22 particles within the sequence.

First, when a sequence contains more than MaxParticleSize (20) particles, it will split up the sequence into chunks of ChunkParticleSize (10). For example, a sequence that has 30 elements would be split into three chunks of 10 elements:

XML Schema Part 0: Primer:

XML Schema provides a mechanism, called substitution groups, that allows elements to be substituted for other elements. More specifically, elements can be assigned to a special group of elements that are said to be substitutable for a particular named element called the head element. (Note that the head element as well as the substitutable elementsmust be declared as global elements.)

The following demonstrates substitution group:

<complexType name="GH6Usage">
  <sequence>

XML Schema Part 0: Primer:

The enumeration facet limits a simple type to a set of distinct values. For example, we can use the enumeration facet to define a new simple type called USState, derived from string, whose value must be one of the standard US state abbreviations:

<xsd:simpleType name="USState">
  <xsd:restriction base="xsd:string">
    <xsd:enumeration value="AK"/>
    <xsd:enumeration value="AL"/>
    <xsd:enumeration value="AR"/>
    <!-- and so on ... -->
  </xsd:restriction>

scalaxb-appengine is a RESTful API to run scalaxb over the web. It's implemented using n8han/Unfiltered and the full source is available on eed3si9n/scalaxb.

compile

URL:

http://scalaxb.appspot.com/compile/{output}.{format}

Formats:

scala, zip

HTTP method:

POST

HTTP encoding:

multipart/form-data

Parameters:

- arg: Optional, multiple allowed. URL of the schema file.
- argf: Optional, multiple allowed. Uploaded schema file.
- defaultPackageName: Optional. Name of the target package.
- namespaceURI: Optional, multiple allowed. URI of namespace to be packaged.
- packageName: Optional, multiple allowed. Name of the target package for the namespaceURI.
- classPrefix: Optional. Prefixes generated class names.
- paramPrefix: Optional. Prefixes generated parameter names.
- wrapContents: Optional, multiple allowed. Wraps inner contents into a seperate case class.

Notes:

- At least one arg or argf must be present.
- The n-th packageName specifies the target package for the n-th namespaceURI.

• Implements support for <group>, <attributeGroup>, and <all>.
• Fixed round trip of complex types containing sequences.
• Generates toXML into the companion objects to simplify the case class.

For example,

<xs:complexType name="Address">
  <xs:sequence>
    <xs:element name="name"   type="xs:string"/>
    <xs:element name="street" type="xs:string"/>
    <xs:element name="city"   type="xs:string"/>
  </xs:sequence>
</xs:complexType>

turns to

case class Address(name: String,

From XML Schema Part 1:

The XML representation for a model group definition schema component is a <group> element information item. It provides for naming a model group for use by reference in the XML representation of complex type definitions and model groups.

The <group> construct allows the schema designers to reuse part of the content model without resorting to type derivation. This comes in handy when dealing with complicated schema. Suppose we have a group named head.misc and an element named head.

• Implements parsing of content models using parser combinators.
• Implements support for xsi:nillable (GH-3).

The following code is an example of a generated parser:

object Address extends rt.ElemNameParser[Address] {
  val targetNamespace = "http://www.example.com/IPO"

  def parser(node: scala.xml.Node): Parser[Address] =
    (rt.ElemName(targetNamespace, "name")) ~ 
      (rt.ElemName(targetNamespace, "street")) ~ 

In XML, one can omit an element to express lack of value or use an empty element.

Sometimes it is desirable to represent an unshipped item, unknown information, or inapplicable information explicitly with an element, rather than by an absent element.

The trouble with using an empty element <foo></foo> is that the emptiness would no longer matches the specified type like xs:positiveInteger. It is possible to form a xs:union of xs:positiveInteger and an xs:enumeration with only empty string in it to allow either poistive integers or empty string. However, technically speaking, an empty string is different from pure emptiness. In terms of code, it's the difference between null and "", or in Scala, None and Some("").

XML Schema resolves this issue by introducing a special attribute called xsi:nil. By writing

<price xsi:nil="true" />

I've known the limitation of hand parsing for a while. Parsing that relies on token positions quickly gets out of hand when there are more complex grammars like repetitions, options, and choices of sequences. At some point, I decided to use scala's parser combinators to do the parsing of content types, but it's been a long way to implement it.

First let's look at a real-life example of such complex structure:

<complexType name="SubjectType">
    <choice>
        <sequence>
            <choice>
                <element ref="saml:BaseID"/>

Added support for mixed contents. in which text nodes are placed in conjunction with subelements within an element. Similar to the way I handled <any>, text nodes are placed in DataRecord[String] object along with other DataRecord objects under a member value called mixed.

Suppose we have a schema that looks like this:

<element name="Element3">
  <complexType mixed="true">
    <choice maxOccurs="unbounded">
      <element ref="ipo:Choice1"/>
      <element ref="ipo:Choice2"/>