IMS Question and Test Interoperability XML Binding

Version 2.0 Final Specification

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Document Name: IMS Question and Test Interoperability XML Binding
Revision: 24 January 2005

Date Issued:	24 January 2005
Latest version:	http://www.imsglobal.org/question/qti_v2p0/imsqti_bindv2p0.html
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1. Introduction
2. References
3. Binding of Complex Types
4. Binding of Simple Types
5. XML Binding Reference

1. Introduction

The information model defines a set of classes and data types in an abstract way. When faced with the real task of communicating data between systems these abstract concepts need to be bound to some physical representation, such as a stream of bytes in a computer file.

The document describes the required method of binding the information model when the physical representation is an XML Document. The binding rules are given primarily in the form of an XML Schema with the following target namespace: http://www.imsglobal.org/xsd/imsqti_v2p0. To assist developers who wish to check the validity of QTI XML documents using tools that support document type definitions (DTDs) the binding rules are also represented as a DTD, however, the DTD is not able to express all the constraints contained in the schema and document instances should validate against the schema. QTI document instances must validate against one of the schema or DTD.

2. References

MathML: Mathematical Markup Language (MathML), Version Version 2.0 (Second Edition); http://www.w3.org/TR/2003/REC-MathML2-20031021/; Published: 2003-10-21
XHTML: XHTML 1.1: The Extensible HyperText Markup Language

3. Binding of Complex Types

Complex types, those that contain other objects through composition and/or have attributes, are represented in the schema as elements with complex content in a straightforward way. Classes that are used as base classes (typically labeled abstract in the model) are used to define an element group consisting of a single choice listing all the non-abstract classes derived from them. Classes with attributes are used to define attribute groups and those that contain other objects (including through inheritance) are used to define element groups describing them.

Elements defined by [XHTML] are not imported directly from an external schema but are instead re-declared as part of the QTI schema. At the time of writing the use of schema for XHTML is at an experimental stage. However, the math element defined by [MathML] is imported from the MathML schema. Note that the use of the MathML schema excludes the use of the entity declarations for mathematical symbols defined in the original MathML DTD and therefore these should not be used for referring to characters within QTI document instances.

4. Binding of Simple Types

Simple datatypes are bound directly to the closest equivalent type in XML Schema, for example, boolean is bound directly to xsd:boolean. Enumerations are bound as enumerated restrictions of xsd:NMTOKEN.

The information model says nothing about how simple types are to be represented in text. For example, the boolean type is an abstract boolean which can be either logically true or logically false. By binding these simple types using XML Schema they automatically inherit the lexical bindings described there. A lexical binding is just a set of rules for representing the abstract type as a run of text characters. For example, XML Schema allows the following strings to represent the values of xsd:boolean: "true", "false", "1" and "0".

XML DTDs have a smaller vocabulary for defining simple types and is therefore not able to impose the same lexical constraints as the schema. Applications that generate QTI document instances that validate against the DTD must still use the same lexical bindings defined by schema even though these will not be checked automatically by the XML parser. For example, in the DTD the boolean type is bound only to NMTOKEN and therefore the XML parser will permit many more strings than the four listed above. However, strings such as "yes" and "no" are still forbidden.