throw a Warning when namespace information are empty

[ymark]

Currently, when the information about a namespace is empty (prefix and URI) an error message is displayed and an exception is thrown.

This situation causes issues since already existing mappings (in 3M) contains empty namespace info in the source_schema block.

In order to remain backwards compatible and allow previous mappings to be managed from the latest X3ML engine, we will throw an error and exception only if one of the fields is missing (either the prefix or the URI).

If both values are empty then, we will simply display a Warning message and continue the execution normally.

[ymark]

The issue has been resolved. The update is available from the (extraordinary) release 1.8.5-1 onwards

[natuk]

This message is still not clear I think. It appears as if there is a problem with the mapping. It triggered me to look at my mapping on 3M for empty entries of namespaces. None was there, so I was left wondering what is going wrong.

[ymark]

Is it the message per se that confuses or the type of the message (Warning) ?

[natuk]

From what I understand, the user can do nothing about the empty prefix and namespace. Also, this does not affect the transformation, correct? So why show a message?

[ymark]

Technically, this should be an error and not a warning. I will explain why.

The empty declarations for namespaces under source_info are the default behaviour of exporting x3ml mappings from 3M editor (https://www.ics.forth.gr/isl/3M).
3M editor assists mapping experts with the definition of the mappings using a user-friendly UI.

X3ML engine is a totally different component, in charge of the transformation and the generation of identifiers and labels for the transformed resources. This means that the engine can use X3ML mappings wherever they come from (3M editor, manually written mappings, etc.). So it validates the mappings wrt the X3ML schema(https://github.com/isl/x3ml/blob/master/resources/X3ML%20Schema/info.xsd). The schema defines that if a namespace element exists, it should contain a prefix and a URI.

After discussing with the engineer of 3M editor (he explained to me why he creates empty namespaces for source_info), we decided to reduce the severity of the message (from error to warning) instead of hiding it completely (which is not correct).