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ordered_members vs. members and their interactions
# How do ordered_members and members behave and interact
# Setup
col1 = Hydra::Works::Collection.new(id: 'c1')
wrk1 = Hydra::Works::Work.new(id: 'w1')
wrk2 = Hydra::Works::Work.new(id: 'w2')
wrk3 = Hydra::Works::Work.new(id: 'w3')
wrk4 = Hydra::Works::Work.new(id: 'w4')
# 1. adding to members does NOT add to ordered members
col1.members << wrk1
col1.members.size # => 1 -- w1
Array(col1.ordered_members).size # => 0
# 2. adding to ordered_members does add to members
col1.ordered_members << wrk4
col1.members.size # => 2 -- w1, w4 (order unimportant)
Array(col1.ordered_members).size # => 1 -- w4
# 3. adding the same object again to ordered_members does NOT add to members
col1.ordered_members << wrk4
col1.members.size # => 2 -- w1, w4 (order unimportant)
Array(col1.ordered_members).size # => 2 -- w4, w4 (precise order)
# add a few more to work with for deletes
col1.ordered_members << wrk2
col1.ordered_members << wrk3
col1.members.size # => 4 -- w1, w2, w3, w4 (order unimportant)
Array(col1.ordered_members).size # => 4 -- w4, w4, w2, w3 (precise order)
# 3. deleting from members does NOT effect ordered_members
col1.members.delete(wrk3)
col1.members.size # => 3 -- w1, w2, w4 (order unimportant)
Array(col1.ordered_members).size # => 4 -- w4, w4, w2, w3 (precise order)
# 4. deleting from ordered_members does NOT effect members
col1.ordered_members.delete_at(2)
col1.members.size # => 3 -- w1, w2, w4 (order unimportant)
Array(col1.ordered_members).size # => 2 -- w4, w4, w3 (precise order)
@elrayle
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elrayle commented Dec 2, 2015

Blend of Approach 2 and 3

Approach 2 could become more intuitive with some adjustments to the API. Currently, it seems like there are two lists (members and ordered_members) being kept for one aggregation. They seem to effect each other in a non-intuitive way. There aren’t actually two lists, but the API treats them in a way that implies they are separate. Trey pointed out in another email that "#ordered_members is a convenience method for returning the proxyFor objects, in order, pointed at from the ordered list.”

A potential change to the API could strengthen the concept that members is a single aggregation. Method changes to support this could be a blend of Approach 2 and 3. Keep the infrastructure currently in place with Approach 2. Change the public methods to be those of Approach 3 where all changes are made to members to effect set operations and ordered list operations. col1.ordered_members would not be a valid call anymore. Instead views into the aggregation as a set or list would be handled by the following methods. NOTE: col1 is an example PCDM:Collection that has aggregation members.

  • col1.members.set - returns each unique member which represents the set
  • col1.members.ordered - returns only members that have proxies which implies ordering (under the covers, this can still be the code run in the current convenience method ordered_members for returning the proxyFor objects)
  • col1.members - by itself returns all members whether they have a proxy or not. This will be a set if no ordering was ever added, a fully ordered list if ordering was always added, or a partially ordered list if some members were added with and some without ordering.

@barmintor
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@tpendragon is that actually specified in PCDM?

@elrayle
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elrayle commented Dec 3, 2015

Actual triples created in Fedora

NOTE: These examples only include triples related to PCDM, ORE, and LDP. Fedora keeps additional triples and each object has additional rdf types that aren't shown here.

Set: Add one work to a collection without order

Code to create set:

col1.members << work1
col1.members << work2
col1.members << work3

Triples in Fedora necessary to represent a set using ORE:

@prefix pcdm:    <http://pcdm.org/models#> .
@prefix ore:     <http://www.openarchives.org/ore/terms/> .

<http://localhost:8983/fedora/rest/dev/col-1> a pcdm:Collection ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-1> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-2> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-3> .

Triples in Fedora for LDP and ORE: (includes the ORE triples from above)

@prefix ldp:     <http://www.w3.org/ns/ldp#> .
@prefix pcdm:    <http://pcdm.org/models#> .
@prefix ore:     <http://www.openarchives.org/ore/terms/> .

<http://localhost:8983/fedora/rest/dev/col-1> a pcdm:Collection, ldp:Container, ldp:RDFSource ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-1/members> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-1> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-2> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-3> .

<http://localhost:8983/fedora/rest/dev/col-1/members> a ldp:Container, ldp:IndirectContainer, ldp:RDFSource ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-1/members/2aa40a84-8011-4bcd-8167-15f115b55d06> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-1/members/62fc559f-641a-43dc-9951-8425ed690037> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-1/members/9cfcdcdd-ab10-4822-9293-c4e100fc96e8> ;
    ldp:hasMemberRelation pcdm:hasMember ;
    ldp:insertedContentRelation ore:proxyFor ;
    ldp:membershipResource <http://localhost:8983/fedora/rest/dev/col-1> .

<http://localhost:8983/fedora/rest/dev/col-1/members/2aa40a84-8011-4bcd-8167-15f115b55d06> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-2> .

<http://localhost:8983/fedora/rest/dev/col-1/members/62fc559f-641a-43dc-9951-8425ed690037> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-3> .

<http://localhost:8983/fedora/rest/dev/col-1/members/9cfcdcdd-ab10-4822-9293-c4e100fc96e8> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> .

Fully Ordered List: Add three works to a collection with order

Code to create fully ordered list:

col2.ordered_members << work1
col2.ordered_members << work2
col2.ordered_members << work3

Triples in Fedora necessary to represent a fully ordered list using ORE:

@prefix pcdm:    <http://pcdm.org/models#> .
@prefix ore:     <http://www.openarchives.org/ore/terms/> .
@prefix iana:    <http://www.iana.org/assignments/relation/> .

<http://localhost:8983/fedora/rest/dev/col-2> a pcdm:Collection ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-1> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-2> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-3> ;
    iana:first <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> ;
    iana:last <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> .

<http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-2> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638588660> .

<http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638588660> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-2> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> .

<http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-2> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638588660> .

NOTE: Each of the list_source proxies should have an rdf type of ore:proxy. Not sure why they don't.

Triples in Fedora for LDP and ORE: (includes the ORE triples from above)

@prefix ldp:     <http://www.w3.org/ns/ldp#> .
@prefix pcdm:    <http://pcdm.org/models#> .
@prefix ore:     <http://www.openarchives.org/ore/terms/> .
@prefix iana:    <http://www.iana.org/assignments/relation/> .
@prefix dct:     <http://purl.org/dc/terms/> .

<http://localhost:8983/fedora/rest/dev/col-2> a pcdm:Collection, ldp:Container, ldp:RDFSource ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-2/list_source> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-2/members> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-1> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-2> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-3> ;
    iana:first <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> ;
    iana:last <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> .

<http://localhost:8983/fedora/rest/dev/col-2/members> a ldp:Container, ldp:IndirectContainer, ldp:RDFSource ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-2/members/bac2feff-8010-4011-9192-de0a79dd13f7> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-2/members/e148c0f5-3038-4311-b39f-0dc4eb7d783a> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-2/members/fd47fa85-08b4-4b27-86d0-329d7d8bc371> ;
    ldp:hasMemberRelation pcdm:hasMember ;
    ldp:insertedContentRelation ore:proxyFor ;
    ldp:membershipResource <http://localhost:8983/fedora/rest/dev/col-2> .

<http://localhost:8983/fedora/rest/dev/col-2/members/bac2feff-8010-4011-9192-de0a79dd13f7> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> .

<http://localhost:8983/fedora/rest/dev/col-2/members/e148c0f5-3038-4311-b39f-0dc4eb7d783a> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-3> .

<http://localhost:8983/fedora/rest/dev/col-2/members/fd47fa85-08b4-4b27-86d0-329d7d8bc371> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-2> .

<http://localhost:8983/fedora/rest/dev/col-2/list_source> a ldp:Container, ldp:RDFSource ;
    dct:hasPart <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> ;
    dct:hasPart <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> ;
    dct:hasPart <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638588660> ;
    iana:first <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> ;
    iana:last <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> .

<http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-2> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638588660> .

<http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638588660> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-2> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099634570060> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> .

<http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638308040> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-2> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-2/list_source#g70099638588660> .

Partially Ordered List: Add three works to a collection with order and 3 without order

Code to create partially ordered list:

col3.members << work1
col3.ordered_members << work2
col3.ordered_members << work3
col3.members << work4
col3.ordered_members << work5
col3.members << work6

Triples in Fedora necessary to represent a partially ordered list using ORE:

@prefix pcdm:    <http://pcdm.org/models#> .
@prefix ore:     <http://www.openarchives.org/ore/terms/> .
@prefix iana:    <http://www.iana.org/assignments/relation/> .

<http://localhost:8983/fedora/rest/dev/col-3> a pcdm:Collection ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-1> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-2> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-3> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-4> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-5> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-6> ;
    iana:first <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> ;
    iana:last <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> .

<http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-2> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-3> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159013851360> .

<http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159013851360> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-3> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-3> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> .

<http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-5> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-3> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159013851360> .

NOTE: Each of the list_source proxies should have an rdf type of ore:proxy. Not sure why they don't.

Triples in Fedora for LDP and ORE: (includes the ORE triples from above)

@prefix ldp:     <http://www.w3.org/ns/ldp#> .
@prefix pcdm:    <http://pcdm.org/models#> .
@prefix ore:     <http://www.openarchives.org/ore/terms/> .
@prefix iana:    <http://www.iana.org/assignments/relation/> .
@prefix dct:     <http://purl.org/dc/terms/> .

<http://localhost:8983/fedora/rest/dev/col-3> a pcdm:Collection, ldp:Container, ldp:RDFSource ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/list_source> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/members> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-1> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-2> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-3> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-4> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-5> ;
    pcdm:hasMember <http://localhost:8983/fedora/rest/dev/work-6> ;
    iana:first <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> ;
    iana:last <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> .

<http://localhost:8983/fedora/rest/dev/col-3/members> a ldp:Container, ldp:IndirectContainer, ldp:RDFSource ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/members/b362baa2-f803-4c6b-b8e8-44a25d64ea71> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/members/be70870b-54c1-4632-8347-d685ec756d44> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/members/c845ffbd-cdc3-42ca-8334-6f61cc20b9c3> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/members/d74e2ea1-dd0d-48b9-a5d7-942d732fc06b> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/members/e0ffc9a7-8934-4ce0-995f-a9ac8d93f554> ;
    ldp:contains <http://localhost:8983/fedora/rest/dev/col-3/members/e1bf5600-860d-47cb-bad4-0326a9376c0a> ;
    ldp:hasMemberRelation pcdm:hasMember ;
    ldp:insertedContentRelation ore:proxyFor ;
    ldp:membershipResource <http://localhost:8983/fedora/rest/dev/col-3> .

<http://localhost:8983/fedora/rest/dev/col-3/members/b362baa2-f803-4c6b-b8e8-44a25d64ea71> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-1> .

<http://localhost:8983/fedora/rest/dev/col-3/members/be70870b-54c1-4632-8347-d685ec756d44> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-3> .

<http://localhost:8983/fedora/rest/dev/col-3/members/c845ffbd-cdc3-42ca-8334-6f61cc20b9c3> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-2> .

<http://localhost:8983/fedora/rest/dev/col-3/members/d74e2ea1-dd0d-48b9-a5d7-942d732fc06b> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-4> .

<http://localhost:8983/fedora/rest/dev/col-3/members/e0ffc9a7-8934-4ce0-995f-a9ac8d93f554> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-6> .

<http://localhost:8983/fedora/rest/dev/col-3/members/e1bf5600-860d-47cb-bad4-0326a9376c0a> a ore:Proxy, ldp:Container, ldp:RDFSource ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-5> .

<http://localhost:8983/fedora/rest/dev/col-3/list_source> a ldp:Container, ldp:RDFSource ;
    dct:hasPart <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> ;
    dct:hasPart <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159013851360> ;
    dct:hasPart <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> ;
    iana:first <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> ;
    iana:last <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> .

<http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-2> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-3> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159013851360> .

<http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159013851360> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-3> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-3> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159014522900> ;
    iana:next <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> .

<http://localhost:8983/fedora/rest/dev/col-3/list_source#g70158983424840> a  ;
    ore:proxyFor <http://localhost:8983/fedora/rest/dev/work-5> ;
    ore:proxyIn <http://localhost:8983/fedora/rest/dev/col-3> ;
    iana:prev <http://localhost:8983/fedora/rest/dev/col-3/list_source#g70159013851360> .

@elrayle
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elrayle commented Dec 3, 2015

The set of triples that are being generated in Fedora do not appear to match the concept of Resource Map described in the ORE spec. If you see this differently, can you explain how you understand this implementation to match ORE Resource Maps?

@tpendragon
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@scherztc
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scherztc commented Dec 3, 2015

What is a use case for a partial_ordered list?

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