updated modified date in iso19139 import

[pvgenuchten]

Description

If a record is written using pycsw-admin utility, the modified date is updated
This value is later used when generating xml, overriding the timestamp value in xml
The xml is no longer similar to the one originally inserted

is it a bug or a feature?

in a use case we replace full catalogue content at intervals using pycsw-admin, and then harvest this content in another catalogue
We use a system in which we compare hash of a record to understand if a record has changed from previous harvest, for us this updated modified date is challenging

Some observations

pycsw/pycsw/core/metadata.py

Lines 1402 to 1403 in 4a27826

	_set(context, recobj, 'pycsw:Date', md.datestamp)
	_set(context, recobj, 'pycsw:Modified', md.datestamp)

Introduces modified date in 2 locations

pycsw/pycsw/core/metadata.py

Lines 1294 to 1301 in 4a27826

	if dt.date_type == 'modified':
	_set(context, recobj, 'pycsw:Modified', dt.date)
	elif dt.date_type == 'creation':
	_set(context, recobj, 'pycsw:CreationDate', dt.date)
	elif dt.date_type == 'publication':
	_set(context, recobj, 'pycsw:PublicationDate', dt.date)
	elif dt.date_type == 'revision':
	_set(context, recobj, 'pycsw:RevisionDate', dt.date)

introduces a modification and revision date, what is the difference?

https://catalogue.ejpsoil.eu/collections/metadata:main/items/doi.org-10.15454-LV9ZRW?f=xml and https://soilwise-he.containers.wur.nl/cat/collections/metadata:main/items/https---doi.org-10.15454-lv9zrw?f=xml have quite different behaviour, in one case modifued is updated in other also publication, difference may be explained in different versions

relates to #1033

is it an option to set a parameter on pycsw-admin not to override modified date, but use the one from original record?