Hi all,
The committers had a special topic meeting today covering Fedora's
relationship to web and semantic web architecture, inspired by some
discussion about Fedora support for Memento, but leading to much bigger
issues than that. I know there are folks who've been in the Fedora
community for a while who have thought about some of these bigger
architectural questions and would be interested, so I'm posting the notes
below and officially inviting anyone who's interested to participate here.
What are some old assumptions that should be challenged, and how do we see
ourselves fitting in with the web, semantic web, and linked data world in
the future? This level of discussion is particularly important for us as we
look toward 4.0. Today's meeting was only intended as a kick-off discussion
-- hopefully we can continue it right here on mailing list in the coming
weeks.
Thanks,
Chris
[Topic areas]
1. What are the major similarities/differences between Fedora and Web
Architecture? The object/resource model. Identifiers, Formats, And
Protocols.
2. Where does Fedora's architecture intersect with or diverge from Semweb
architecture?
3. Should Memento support be added directly to Fedora's REST API, or
considered as a higher-level service (extension) on top of it?
[Notes from Feb 23rd 2012 committer call]
Chris: Start with how Fedora fits/doesn't fit into web architecture. Dan
has called Fedora a "Resource Store" vs a "Content Store". How does this
concept of resource differ from web arch's concept?
Adam: CMA and dissemination architecture. A key distinction is that
Fedora's dynamic representations are highly specified, and the
specifications themselves are resources.
Chris: So is Fedora just filling in details, or does it actually go in a
different direction from web arch?
Adam: Fedora's object model is different. It's disseminations also look an
awful lot like member functions in OOP.
Steve: It's also about fundamental responsibilities. Fedora's about
curation and dissemination. Fedora makes a distinction about identifying
the representation as a thing to be preserved!
Dan: I believe Adam said "An archive needs to care how a representation is
created."
Adam: Sounds good, I'll take credit.
Dan: Hourglass design: push complexity to the edge and have simple stuff
(verbs, object models) in the "waist".
Adam: Fedora's dynamic disseminations haven't got a lot of uptake.
Chris: Complexity, approachability.
Dan: Maturity.
Adam: History…things have changed with Fedora. More emphasis now on the
graph of objects and relationships. Change ok.
Dan: Also CMA. And people haven't experimented with alternate ideas for
content modeling as much as we'd hoped.
Adam: ECM has. Others haven't in part because it's too hard.
Chris: What about the REST api? Where do we fight the web architecture &
REST?
Adam: Orchestration tools/APIs tend to be RPC-based, not resource-based.
Usually you talk about operations with SOAP. A REST API doesn't fit as well
there.
Dan: Gigantic strength in seeing Fedora as middleware and not as a
repository. Having different interfaces is important.
Chris: REST doesn't define Fedora, nor does SOAP. Still feel both are
important. Advantages of REST API over SOAP? Big one in my mind: ease of
integration with existing languages/tools. Success with SOAP tool interop
has historically been mixed, though it's getting better.
Adam: (agree on SOAP tool interop)
Frank: Also if you adhere to REST, you get some things for free. Caching on
top of Fedora via Apache. Can't do with SOAP API.
Dan/Chris: Method-for-method equivalence of REST api and SOAP is not
necessary. But overall capabilities should be comparable.
Dan: Fitting Fedora into a grand eventing architecture?
Chris: Steve has suggested that more generic, resource-oriented events
would be good to publish from Fedora. Advantage is integration with more
generic (non-Fedora-specific) tools. Today we have Fedora-specific
event-based messages coming out. Need for both approaches?
Steve/Others: Yes. Seems both have their place.
Adam: On any given interface to Fedora, it seems like we want to consider a
Fedora-event-oriented exposure and a more generic resource-oriented
exposure.
Chris: Now, where do things seem weird with semweb architecture and Fedora?
Frank: Having ids for all Fedora entities makes sense. Referencing via URI.
Chris: Use of the info: scheme seems to be one place we fight some accepted
semweb guidelines (linked data says http-only). The info-uri effort has
been discontinued, but thankfully, it wasn't designed with resolution in
mind so Fedora info: URIs will continue to be useful.
Adam: A fundamental difference: In Fedora, the only place where I can make
an RDF assertion is inside the object that the assertion is persisted.
Chris: I'd qualify that – you can make whatever RDF assertions you want
about Fedora object, but if you want them indexed by today's Fedora RI we
have certain restrictions on that.
Adam: Steve presentation at OR: Pattern we've seen with Fedora is that
public ids have been exposed through some other system, not Fedora. Fedora
has internal ids.
Steve: Was a "what if": Fedora as the curator of the public ids? Valid to
have an internal representation and a different public exposure of that
model, and a transformation between those things.
Adam: Community seems to prefer not to use info: uri as public identifier.
Dan: Nuanced conversation. Asking to potentially build some new core ideas.
Web arch. allows for private resolver systems. Was thinking of ideas that
came out of SOA community, notion of Fedora ecosystem providing a private
resolver system. A system for being an authority source for identifiers.
Dan: If we provided technology or specifications for the IFAPs (Interfaces,
Formats, And Protocols) for federating Fedora, we can facilitate
communities who are actually putting federations together.
Steve: Fedora has a role as registry repository.
Dan: Can act as resolver system, but can be made better.
Adam/Chris: Should Fedora's REST api endpoints be considered Durable or
Linked Data Friendly?
Dan/Chris/Adam: We should be very clear about that.
Dan: Also Fedora needs to re-address notion of versioning and migration.
Fundamental pattern of a bolt-on in Fedora to handle migration. Might not
be all of memento.
Chris: If REST API is not intended to provide durable ids for things,
memento doesn't belong there.
Dan: We often leave out the Federation of repos.
Steve: Believe it's very important that Fedora have an internal id.
Chris: Using URIs for internal ids works well today because we have
standards (rdf) to relate them.
Frank: What about UUIDs? Easy to generate.
Chris: Also URI-compatible. It's convenient in any case for Fedora to
continue allowing people to mint ids outside the repository.
Adam: Anti-pattern we see a lot of: putting semantics in ids. But human
nature.
Steve: From a long term preservation perspective, you'd want to isolate
yourself from current trends, standards.
Chris: Riding waves is good, but we're not defined by them.
--
Notes from
https://wiki.duraspace.org/display/FCREPO/2012-02-23+-+Special+Topic+-+Fedora%2C+Web%2C+and+SemWeb+Architecture
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