XML Mapping Additions Ratio
This metric asks the question “How many fields are in the intended schema that are not in the original schema?” It can be used to judge whether adopting a standard schema unchanged will have the (possibly unintended) consequence of adding extra elements or attributes to support.
The metric is two numbers; the absolute values are of at least as much interest as the relative values, so we express them as a ration not a percentage. The ratio is formed using the following method:
- For the left-hand side, in the “from” schema count all “fields” (as defined earlier) which have adequate mappings to fields in the “to” schema. (This is the same as the right-hand side of the XML Mapping Completeness Ratio above.)
- For the right-hand side, count all fields of the “to” schema.
For example, the address examples above have a ratio of 6:8. The elements alley and street are additions with no equivalent in the “from” schema. This result indicates that there are extra elements or attributes that need to be coped with.
A project manager can easily ask for technical staff to derive these metrics. If both are 1:1, there is a perfect match. If the XML Mapping Completeness Ratio is not 1:1, then the new schema is not suitable; a check also should be made whether in fact the unmapped elements are actually used of course. The further that the
XML Mapping Additions Ratio diverges from 1:1, the more extra capability is being added that is not required for mere mapping purposes; if these extra capabilities and attendant costs do not correspond to a business requirement, the “to” schema should be pruned if possible or otherwise is probably not suitable.