Open Operator

A library of common QTI custom operators and documentation to enable compatible cross-vendor and cross-language scoring implementations.

Actively seeking recommendations and review of operator design and implementation.

Implemented Operators

pointX

Retrieves the horizontal integer sub-value from values of the "point" base type.

pointY

Retrieves the vertical integer sub-value from values of the "point" base type.

distance

Calculates the total distance from one point to a next for a series of points.

parseFloat

Parses a single float from a single string.

parseInteger

Parses a single integer from a single string.

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Detailed operator documentation can be found in the class descriptions.

Stand-alone assessment item XML files demonstrating use of the custom operators may be found in the src/test/resources/openoperator/operators directory.

Planned

• More Operators:
• Advanced substring slicing (e.g. "string contents prior to first instance of substring within target string")
• Set manipulation and inspection
• QTI XML implementations of all custom operators not requiring fundamentally new primitives.
• Non-Java reference implementations of operations.
• Documentation
• Guiding practices for operation behavioral patterns
• Expand wiki documentation of operators to reduce the time people have to spend looking through the code files.
• Formalize (and automate) code style guidelines
• Describe collaboration guidelines
• XML item examples with non-dummy item bodies containing relevant interactions and making advanced use of the operators in nontrivial processing rules..

Documentation Expectations

Operator behavior should be clear. The documentation should provide guidance on how the operator will behave under a variety of conditions.

Answering the following questions should be a reasonable starting point for ensuring thorough operator design and implementation.

• How many sub-expression children (inputs) are permitted? Is it a range or a set number?
• What happens if there are more or fewer children than permitted?
• What cardinality and base type of sub-expression children (inputs) are permitted?
• If the order of child sub-expressions were changed, how would that affect the output?
• If the child sub-expressions must be in a particular order, do those sub-expressions have different allowed cardinality or base type?
• What is the cardinality and base type of the operator's result output?
• Does the output cardinality and base type depend on the base type or cardinality of the input sub-expression children?
• Does the output cardinality or base type depend on the number of input sub-expression children?
• What is the output if any one of the input sub-expression children is NULL?
• What is the output if all of the input sub-expressions are NULL?
• For numerical operators, what happens if any one of the input sub-expression children is "NaN"?
• Is it ever possible for the operator to produce a "NaN" result? (NaN is distinct from NULL)