This page is a subpage of [[CMDI 1.2]]

= MdType instance header element = 

[[PageOutline(1-4)]]

== The issue ==

Originally described in [[CmdiCollectionsIdentification]]

Due to the difference in granularity it might be good to be able to select CMD records of a specific granularity, e.g., collection or item level.

==== Discussion ====

[[schiel|Florian]]: Why restrict this to a a two-level granularity 'collection' and 'part_of_collection'? Most of us agree that relations between MD instances are necessary and should be made possible (see for instances the discussions in the VLO task force group). The very first relations that all MD providers using hierarchical MD structures will apply are 'is_part_of' and 'has_part'. Once these relations are encoded, you don't need any rigid two-level granularity as proposed here: just the fact that a relation 'is_part_of' is present indicates that this MD cannot be the root of a resource. In fact both relations are already used in CMDI 1.1: namely the header element 'isPartOf' (= relation 'is_part_of') and the ResourceProxyLink of type 'Metadata' (= relation 'has_part').
To my knowledge even in IMDI unrestricted hierarchies have been used. In the current CMDI at least the centers BAS and IDS uses relations like above. Relations will make MdType obsolete.

== Proposed solutions ==

=== First solution: MdType header element ===

A new header element that indicates the type.

==== Pros ====

Easy

==== Cons ====

There can be a tendency to keep on extending the header instead of using CMDI's flexibility.

==== Centre impact ====

* Affected tools
* Impact on instances

==== Implementation examples ====

* Implementation on model level
* Implementation on instance level

==== Discussion ====

[[herold|Axel]]: This would work if we agreed on a fixed set of types, ideally with just two elements (collection, part_of_some_bigger_collection). But as always there is no sharp line to be draw between even those two values. E.g. for the Deutsches Textarchiv (a collection of digitalized complete printed book) one could argue that each part is also a complete and self-contained resource in its own right -- it just happens to have been arbitrarily chosen for inclusion in the Deutsches Textarchiv. Maybe we would need to introduce a third type 'archive' for cases like those?

=== Second solution: the one and only collection profile ===

One collection profile to be used by all.

==== Pros ====

Easy

==== Cons ====

Inflexible

==== Centre impact ====

* Affected tools
* Impact on instances

==== Implementation examples ====

* Implementation on model level
* Implementation on instance level

==== Discussion ====

[[herold|Axel]]: We shouldn't go this route. It's so inflexible that it is hard to imagine such a catch-all profile will ever stabilize. We would end up with a whole family of profiles anyway once profile versioning is in place.

=== Third solution: a mandatory collection component for collection profiles ===

Any collection level profile should contain a specific CLARIN collection component.

==== Pros ====

Easy, may have low impact if the component is optional (but can be detected in the schema)

==== Cons ====

What should be in the component?

==== Centre impact ====

* Affected tools
* Impact on instances

==== Implementation examples ====

* Implementation on model level
* Implementation on instance level

==== Discussion ====

Discuss this solution proposal in this section

=== Fourth solution: the profile root uses a data category from a collection relation set ===

The profile root should use one of the data categories from a specific collection relation set in RELcat.

==== Pros ====

Easy, low impact

==== Cons ====

Data category might be unintentionally used 

==== Centre impact ====

* Affected tools
* Impact on instances

==== Implementation examples ====

* Implementation on model level
* Implementation on instance level

==== Discussion ====

Discuss this solution proposal in this section

=== Fifth solution: collection level instances are harvested from a specific OAI-PMH set ===

Like done for web services collection CMD records can be explicitly requested by harvesting a center specific OAI-PMH set.

==== Pros ====

No need to touch CMD profiles or instances

==== Cons ====

VLO currently doesn't use endpoint information, i.e., the facet mapping can't select based on the OAI-PMH endpoint or set.

==== Centre impact ====

* Affected tools
* Impact on instances

==== Implementation examples ====

* Implementation on model level
* Implementation on instance level

==== Discussion ====

[[herold|Axel]]: No, this is a dirty hack, i.e. a tailor made solution for VLO harvesting outside of the CMDI framework proper. Collection information must be expressed within the CMDI framework so that it is available not only at harvest time but also within MD instances.

== Tickets ==
{{{#!comment
Below replace the word 'keyword' in both the the text and the ticket query
}}}
Tickets in the CMDI 1.2 milestone with the keyword ''mdtype'':
[[TicketQuery(keywords=~mdtype,milestone=CMDI 1.2,format=table,col=summary|owner|component|priority|status)]]

== Discussion ==

Discuss the topic in general below this point