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JSON-LD Telecon Minutes for 2012-02-07

From: Manu Sporny <msporny@digitalbazaar.com>
Date: Mon, 13 Feb 2012 08:52:02 -0500
Message-ID: <4F391582.7080309@digitalbazaar.com>
To: Linked JSON <public-linked-json@w3.org>
Thanks to Dave Lehn for scribing! The minutes for last week's call are
now available here:

http://json-ld.org/minutes/2012-02-07

Full text of the discussion follows, as well as a link to the complete
audio transcript:

--------------------

JSON-LD Community Group Telecon Minutes for 2012-02-13

Agenda:
    http://lists.w3.org/Archives/Public/public-linked-json/2012Feb/0002.html
Topics:
    1. ISSUE-46: Absolute IRI detection
    2. @list - type coercion
    3. ISSUE-54: Arrays of IRIs
Resolutions:
    1. If a key in a JSON-LD document contains a colon, it is a
       CompactIRI if the prefix is defined as a term in the active
       context, otherwise it is an AbsoluteIRI. The only exception to
       this rule is if "//" follows the first colon, and in that case,
       the value is an AbsoluteIRI.
    2. If a key in a JSON-LD document contains a colon and the
       first colon is not followed by "//", it is a CompactIRI if the
       prefix is defined as a term in the active context, otherwise it
       is an AbsoluteIRI.
    3. Adopt "@container": "@list" syntax to specify container
       coercion to an ordered list when specified via the @context.
Chair:
    Manu Sporny
Scribe:
    David I. Lehn
Present:
    David I. Lehn, Manu Sporny, Gregg Kellogg, Niklas Lindström

David I. Lehn is scribing.
Manu Sporny:  Any additions to the agenda?
Manu Sporny:  I read through every issue this weekend and tried
    to understand where issue logger was coming from and come up with
    solution that might get consensus. Some proposals worked out and
    some did not. We'll handle those as we go.
Manu Sporny:  Would anyone have time next week for a 2 hour super
    session?
Gregg Kellogg:  yes
Niklas Lindström:  maybe
Manu Sporny:  Alternative is to go through issues and say which
    proposals you agree with. Can ask Markus to do the same and make
    some headway.
Manu Sporny:  Maybe we can get people to put comments on the
    mailing list.
Gregg Kellogg:  My talk was accepted at SemTechBiz in San
    Francisco in June.
Manu Sporny:  Awesome! Very cool. Great, the first mention of
    JSON-LD at a conference.
Gregg Kellogg:  Should be timeline, hopefully we get through more
    issues by then!
Manu Sporny:  Hopefully we get through them and no one raise any
    more!

Topic: ISSUE-46: Absolute IRI detection

Manu Sporny: https://github.com/json-ld/json-ld.org/issues/46
Manu Sporny:  Issue related to how you figure out what a relative
    IRI is and what an absolute IRI is. The proposal is if key
    contains a colon then it's a compact IRI if the prefix is in the
    active context, otherwise it's an absolute IRI. Basically saying
    there are no relative IRIs on the left hand side. Hopefully
    that's in line with discussion from last week. Anyone opposed to
    that proposal?
Gregg Kellogg: SemTechBiz in San Francisco this June
Niklas Lindström:  Did you say anything about keys defined?
Manu Sporny:  Yeah. If the key has a colon in it then you split
    on the colon and look up the prefix in the context. If that's
    there then you expand it, or rather you say it's an CURIE and the
    prefix is defined in the context. If the prefix is not defined in
    the context then it is an absolute IRI. mailto: would be a good
    example of that.
Niklas Lindström:  I'd really like that safety mechanism that we
    did in RDFa as well, the double slash.
Manu Sporny:  I'm wondering if we need that safety mechanism is
    JSON-LD. The reason I don't think we need it is I don't think
    someone is going accidentally put in http:// and need it to be
    anything other than an absolute IRI in JSON-LD in the key
    position.
Niklas Lindström:  But that's an argument for because not meaning
    it to be an absolute that's the intent of preventing the
    expansion of anything that begins with double slash. Most of this
    is theoretical but there the case where you create JSON-LD from
    RDFa and that RDFa would be careless about using old http prefix.
    Same thing goes for any other protocol. It's the same reasoning
    as in RDFa. My argument here was that we don't know how the
    JSON-LD is going to be created so if you use external definitions
    for prefixes and also since we don't differ between prefixes and
    terms we will have a lot more definitions which might
    accidentally collide with some scheme. The risk might be greater
    than with RDFa.
Manu Sporny:  I could go either way on it. I think it's a valid
    argument but I don't know how high the risk is. I'm concerned
    with putting in features that prevent things that are not a high
    risk. Anyone have input on this?
Gregg Kellogg:  If you were to take an RDFa document and
    transform it to JSON-LD where there was confusion in the RDFa
    document that prevented the thing from being interpreted as a
    CURIE would it now look like a CURIE because of the environmental
    prefixes. Would you end up with a different interpretation? I'm
    not sure if that would happen or not.
Manu Sporny:  The RDFa processor would probably convert it to
    JSON-LD from the triples not from the raw text. In RDFa you would
    emit an IRI not a text string.
Gregg Kellogg:  You would tend to pull over your same prefixes so
    you can output a document that looks good. So if you pull over
    your prefixes and use them to define CURIES you might have an
    issues. We probably need a concrete use case to see how that
    would work. It seems at this point is the lifecycle of JSON-LD it
    would add some more complication which might make it more
    difficult to get people to adopt it. The advantage of your
    proposal is that it is very simple.
Manu Sporny:  There is an argument here that I can see this
    happening during Last Call just like it did for RDFa.
Niklas Lindström:  The thing is that it will go unnoticed until
    it appears and then there is no way to stop it. I've been scared
    of this potential risk since last summer because it looks so
    innocent until it really corrupts your data. And Shane also
    discovered the widget URI scheme, which is called "widget", and
    it's not inconceivable for someone to define at least a term
    called widget. Given that we have those intermingled, there is no
    different between terms and prefixes. It feels uncomfortable to
    me.
Manu Sporny:  The proposal would change that says that any key
    that contains "://", where two slashes are after the first colon,
    would be an absolute IRI. Any issues with that?
Gregg Kellogg:  I'm fine with it.

PROPOSAL:  If a key in a JSON-LD document contains a colon, it is
    a CompactIRI if the prefix is defined as a term in the active
    context, otherwise it is an AbsoluteIRI. The only exception to
    this rule is if "//" follows the first colon, and in that case,
    the value is an AbsoluteIRI.

Manu Sporny: +1
Gregg Kellogg: +1
Niklas Lindström: +1
Niklas Lindström:  We should change the contains a colon in
    either case because it could contain more than one colon.
Niklas Lindström: If a key in a JSON-LD document contains a colon
    and the first colon is not followed by "//"...
Manu Sporny:  I was going to say we could just edit the document
    and put the right thing in and people will complain if it's not
    right.
Gregg Kellogg:  Do we have wording from RDFa?
Manu Sporny:  We do.
Gregg Kellogg:  Is it worse?
Manu Sporny:  How about this, I can resolve the proposal and then
    we can clarify.
Gregg Kellogg:  Maybe we can define a regex for it.
Manu Sporny:  Yeah we need ABNF or something.
Niklas Lindström:  We're going to get that for RDFa so we can
    piggyback on that.
Manu Sporny:  I don't know if JSON-LD is more forgiving than
    RDFa. The intent was for it to be but we might not need to do
    that. And we might as well get two languages that have CURIES
    aligned.
Gregg Kellogg:  I wonder if would could reference RDFa? We've
    avoided doing that by not even calling it a CURIE but in the API
    document maybe it isn't so bad to have it more closely aligned.
    This is a place I imagine Markus not entirely agreeing with the
    reasoning here.
Manu Sporny:  Let's go ahead and resolve this issue and if Markus
    thinks there's an issue we can open or discuss it again. There's
    still consensus and unless he's a -1 we'll still end up doing it.
    I'll go ahead and resolve this and then we can clarify it.

RESOLUTION: If a key in a JSON-LD document contains a colon, it
    is a CompactIRI if the prefix is defined as a term in the active
    context, otherwise it is an AbsoluteIRI. The only exception to
    this rule is if "//" follows the first colon, and in that case,
    the value is an AbsoluteIRI.

Niklas Lindström:  Did you see my potential folding in of the not
    followed by double slash note?
Manu Sporny:  Is that for the beginning of the resolution?
Niklas Lindström:  Exactly, because instead of having to deal
    with the exception in the second sentence we could have that.
Manu Sporny: Clarification - you always split on the first colon.
    The rule only applies to the first colon detected in a CURIE, all
    subsequent colons are allowed.

PROPOSAL:  If a key in a JSON-LD document contains a colon and
    the first colon is not followed by "//", it is a CompactIRI if
    the prefix is defined as a term in the active context, otherwise
    it is an AbsoluteIRI.

Manu Sporny: +1
Gregg Kellogg: +1
Niklas Lindström: +1

RESOLUTION: If a key in a JSON-LD document contains a colon and
    the first colon is not followed by "//", it is a CompactIRI if
    the prefix is defined as a term in the active context, otherwise
    it is an AbsoluteIRI.

Topic: @list - type coercion

Manu Sporny: https://github.com/json-ld/json-ld.org/issues/60
Manu Sporny:  This particular issue has to do with changing the
    list syntax from "@list":true to something else. What was
    suggested "@container":"@list". The proposal is specify that
    @list type coercion occurs when in the @context,
    "@container":"@list" is specified for a particular for a compact
    or absolute IRI. Markus raised something that was pretty
    interesting. He suggested lets not have an @container keyword and
    use @type with @list.
Gregg Kellogg:  This was actually one of the things we considered
    back when we went to @list. There were a number of different
    options and one was to include it in the @type. At the time we
    decided to not do that. We'd have to go back in the minutes and
    see where that discussion occurred. My thinking was the reason we
    didn't do that was that @list isn't a type. @type really relates
    to coercion of plain strings and @list relates to coercion of
    arrays. They are different things and this is an example of
    revisiting something we already determined.
Manu Sporny:  Good point.
Niklas Lindström:
    https://github.com/json-ld/json-ld.org/issues/44
Niklas Lindström:  This is also discussed in ISSUE-44 which is
    specifically about sets. We intended this to supported by the
    same syntax or at least in the future be allowed to use the same
    syntax. Markus raise the same point as well. My three last
    comments there go into details. There is a question if this
    property for a term definition should also be a part of the
    identity of a term. That is, if you have multiple terms how do
    you select one of them. For instance, you could have one term
    called creator and one called creators. If you have multiple
    creators you use one term otherwise use creator. But that is
    specifically for sets because in lists that wouldn't apply. I
    noticed that if we used @type for lists instead of @container it
    would follow the fact that type is considered when we determine
    which term to use.
Gregg Kellogg: We discussed this in issue 40:
    https://github.com/json-ld/json-ld.org/issues/40
Manu Sporny:  I think what Gregg mentioned resonates with me. Do
    we want to be that accurate/pedantic or will we allow a bit of
    leeway. Right now we're already doing that with @type and are a
    bit fuzzy. It's used to set the coercion type, the RDF type, and
    the data type of a value.
Manu Sporny:  Where's the fuzzy gray line? Is using list in set
    going to far?
Niklas Lindström:  If you want to use coerced values you either
    would use Markus example with the value of a type being a list,
    with the values being @list and the coercion type. If we go that
    way, I this notation would be clearer.
Niklas Lindström: .. "@type": {"@list": "xsd:date"}
Manu Sporny:  The array notation?
Niklas Lindström:  No the object notation.
Gregg Kellogg: 1) "foo": {"@iri": "http://uri.foo", "@coerce":
    ["xsd:date", "@list"] }
Gregg Kellogg: 2) "foo": {"@iri": "http://uri.foo", "@coerce":
    "xsd:date", "@list": true}
Gregg Kellogg: 3) "foo": {"@iri": "http://uri.foo", "@datatype":
    "xsd:date", "@list": true}
Gregg Kellogg: 4) "foo": {"@iri": "http://uri.foo", "@list": {
    "@datatype": "xsd:date" } }
Gregg Kellogg: 5) "foo": { "http://uri.foo": { "@list":
    "xsd:date" } }
Gregg Kellogg:  Those are Markus variations he specified in
    ISSUE-40. You'll have a lot of different types of syntaxes
    depending upon the combinations of things that you might do. What
    if list is specified for one term for another term and both terms
    map to the same IRI. Then you've got more complications when you
    do expansion vs compaction. You expand and merge two things. When
    you compact, which term you select is going to determine if there
    is list compaction or not. Yet another reason why that should be
    done on the expanded IRI rather than the original term. In any
    case there's a lot of different semantic variations that you
    could go through. So when you are parsing you look for type is
    list, type is date, type is an array of list and date, or type is
    an object of list and date. I think we're just making some real
    potential problems in implementing the algorithms when we
    increase these variations.
Manu Sporny:  The one fear I have here is that we're heading down
    the same path that RDFa went down which is that all these things
    seems simple on the surface but when you get to the final
    processing rules it's incredibly difficult to figure what's going
    on. You can't keep it in your head and have to run it against a
    processor to see what pops out. I'm concerned were getting close
    to that. You need something that you can just look at and tell
    what's going on.
Niklas Lindström:  The syntax variations is only on the surface.
    If you use @container or a complex value for @type they mean
    semantically the same. Therefore I reasonable favor @container
    over a structured @type value since you have to do a lot of
    checking to parse it and it's not as immediate as looking at
    something and seeing @container.
Gregg Kellogg:  I think the @container syntax makes sense when
    you've got something other than @list that you might want to use.
    So "@container":"@list" allows for more options when we go
    forward. So if we were to add set we possibly could piggyback on
    that for a mechanism that indicates that things are always in an
    array notation.
Niklas Lindström:  I need some way to do that, and if I don't
    have support for sets I have to do it in the API documentation
    and the consumers won't readily be able to see it from the
    context.
Gregg Kellogg:  If we were to combine that with @type, then it
    might be something like @type would be @set and date, and the
    combination of list and set would be illegal if we were to
    combine these together.
Manu Sporny:  What do you mean by combine?
Gregg Kellogg:  Use the array notation that was originally
    suggested on this issue.
Niklas Lindström:  The array or object notation would have to
    restrict what you are allowed to write in a non obvious way. I
    think @container is better. It's clearer and flatter.
Manu Sporny:  Sounds like we have consensus around that. At least
    I agree. It sounds like you all agree it would be better to use
    @container at this point?
[all: yes]
Manu Sporny:  So there would be two proposals.
Niklas Lindström:  That's for ISSUE-44 right?
Manu Sporny:  Yeah. The key thing here is that we're not saying
    that we won't support @set, we just haven't made a decision on
    that. We may not make a decision on that for JSON-LD 1.0 even
    once we revisit ISSUE-44. In that case we still don't want to
    prevent its use in the future. It could be we have something in
    the future like "@container":"@graph". But that's far in the
    future.

PROPOSAL:  Adopt "@container"

Niklas Lindström: +1
Gregg Kellogg: +1
Manu Sporny: +1
David I. Lehn: +0
Niklas Lindström:  That solves ISSUE-60 right?
Manu Sporny:  I've got two proposals that addresses ISSUE-60,
    this is the other one.
Niklas Lindström:  ISSUE-60 is only about list coercion. ISSUE-44
    mentions sets.

RESOLUTION: Adopt "@container": "@list" syntax to specify
    container coercion to an ordered list when specified via the
    @context.

PROPOSAL:  Do not support "@container"

Manu Sporny:  The other proposal that comes along with this is
    that we're not going to support "@container":"@set" at preset.
    Niklas, you think that we should save that proposal until we
    discuss ISSUE-44?
Niklas Lindström: -1 for the first part, +1 for the second...
Niklas Lindström:  My vote for this proposal looks like that. I'm
    against not supporting "@container":"@set" at present because I
    want to support it. That implies that I don't want to prevent it
    in the future.
Manu Sporny:  I confused myself while looking at ISSUE-44 and
    copy & pasted the proposal. That resolves ISSUE-60 as well.
    ISSUE-60 is off the table and we'll talk about ISSUE-44 at some
    point in the future.

Topic: ISSUE-54: Arrays of IRIs

Manu Sporny: https://github.com/json-ld/json-ld.org/issues/54
Manu Sporny: {"@id": ["a", "b"]}
Manu Sporny:  Markus has said what do we do when you have an @id
    and an array of text strings that are basically IRIs? What do you
    output? We had interesting suggestions on what kind of triples we
    could output. Markus and Gregg got into a long discussion about
    what we could do. I think in the end I have a concern that we may
    be shooting ourselves in the foot allowing this syntax. We had
    considered this syntax, but the way we considered it was that you
    would be allowed to set properties for multiple IRIs. Let's say
    you had a huge document database and wanted set the copyright for
    all documents, you would use @id and list all the IRIs in an
    array and the next item would be the property like license or
    copyright. But we've since backed away from that and don't
    support it in JSON-LD now. But we do allow an array of multiple
    objects, which is how we do disjoint graphs.
Gregg Kellogg:  There were a couple of proposals put out there.
    When I was going through and looking at lists originally, we were
    looking at the double array paradigm. A double array in this
    circumstance would make it clear you were making a list. We could
    also say that list coercion is implied on @id so that the use of
    that in and @id would create a list of these subjects. So in the
    case where this is part of a block which is an object with
    properties, it would be defining the subject as a list and
    properties on that list. In the case where there were no
    properties you would basically be defining a list. Which is
    pretty much equivalent to how you would do those things in
    turtle.
Manu Sporny:  I'm having a hard time following.
Gregg Kellogg: ("a" "b") a rdf:LIst
Gregg Kellogg:  I think you can do that in turtle. You can do it
    in N3, but it's possible it's been restricted since then. That
    would be equivalent to saying
Gregg Kellogg: {"@id": ["a", "b"], "@type": "rdf:List"}
Gregg Kellogg:  If list coercion was implied, that's what this
    statement would be. Of course saying it's an RDF list is
    redundant, but there's other things like provenance information
    you might use in there too. It reconciles the use of an array in
    this term in a way we already deal with.
Manu Sporny:  There are multiple ways we could interpret that and
    it's not clear to me what the best way of interpretation is. I
    don't think we necessarily have a use case for the example you
    mentioned. I don't think we have a use case from what Markus is
    suggestion. I think we should just try and do something that is
    somewhat future proof. So we throw an exception if somebody puts
    a string value in an @id array. If that array doesn't consist
    entirely of objects we either pick the first string in the @id
    array or we throw an exception and say not to use this syntax
    yet. I think it would be easy to add some sort of feature but it
    is premature because we don't have anyone screaming for the
    feature and it adds complexity to the processing rules.
Gregg Kellogg:  This does sort of relate to Markus thought about
    having a document that implements a list that you can then
    reference. By doing it with this form you can have an @id with a
    list of elements and it can have a URL that can be refereed from
    another document.
Niklas Lindström: .. referencing lists:
    https://github.com/json-ld/json-ld.org/issues/75
Niklas Lindström:  That was related to what I was thinking about
    and tried to shake out in a turtle document. I'm not sure if
    that's possible in turtle and may only be in N3. I thought it
    wasn't because RDF lists are special creatures. I comment on
    ISSUE-75 about provenance and lists at the top level. It's an
    edge case. The entire list is a special structure and annotating
    it itself is saying something about an expression which is itself
    abstract and technical and low level.
Gregg Kellogg:  You can say this in turtle because the production
    is a blank node, a blank node property list, or a collection. And
    the subject can be an IRI or blank. The difference between turtle
    and N3, in N3 you can declare a list without having a predicate
    on it. In turtle there must be a predicate if it's in the subject
    position.
Manu Sporny:  I feel we're getting into esoteric territory here.
    My concern is this adds some amount of complexity. There's also
    complexity that they have to understand this new mechanism. I'd
    argue this is different than the disjoint graph mechanism. Gregg
    you're proposing if they have an array of items with @id, then a
    list is implied. But if we have and @id with an array with
    objects in it then the implied type is that it's a disjoint
    graph. Now I'm wondering what if you add an property to that? Is
    it a property off of the list and property off of the disjoint
    graph or something else?
Gregg Kellogg:  My proposal is that if you have an @id that
    references an array then you are defining a list. So we have the
    current usage where you have an @id defining an array of objects
    that define ids that is used only for disjoint graphs. There has
    been some other discussion that the use of @id in that
    circumstance is confusing and perhaps we should consider
    replacing it with something such as @data. That would reconcile
    this thing. It's nice to be able to have a way to take legal JSON
    and provide a way it's interpreted in JSON-LD without restricting
    that form. There are cases where I disagree with that, for
    instance a literal who's value is an array but being able to make
    some sense of an @id that has an array does make the language
    more consistent. Just saying @id has an implied list coercion on
    it somewhat addresses that. That would allow you to override that
    to say a set by coercion of @id to "@collection":"@set" in a
    context, if that's something we choose to do.
Manu Sporny:  I still see a lot of complexity being added here.
    If we do remove the @id multiple object array syntax then we are
    simplifying the language which is positive. If we are making such
    that we allow that and do the simplification and have this extra
    complication and have "@id":["a","b"] and making that
    automatically coerce to a list, I do think that it makes the
    language more uniform but I don't know if adding that complexity
    is going to help the vast majority of people offering documents.
    I don't think I've ever seen any turtle that does what we're
    talking about. It may be in examples but I can't see anyone
    actually using it.
Niklas Lindström:  A reflection on what Gregg said, if the value
    for @id was allowed to be a list and by default it would be a RDF
    list, but if you coerced it to a set, it would be a set. I think
    that would imply that the original @id [...] regarding using
    multiple subjects for the same statement. In general I agree we
    should defer this and note it's a possibility somewhere so we
    don't forget this perspective. Is it a list as subject or a macro
    for creating multiple statements. I agree we should defer it at
    the moment since it's quite complicated.
Manu Sporny:  Markus agrees in the issue tracker without hearing
    Gregg's argument. What's he's suggesting we throw an exception if
    we detect an @id and it has list and any item in the list is a
    string.
Gregg Kellogg:  Is it constrained to just about items being
    stings? I've been interpreting this issue as any use of an array
    with @id. Presuming we address the top level issue of considering
    something like @data. Seems the issue is if it's a sting or not.
Niklas Lindström:  What happens if it is an object or a boolean?
Gregg Kellogg:  If it's objects its still the same problem. What
    is it you are declaring? I think the proposals were pick the
    first, pick the last, raise an exception. I'd be fine with
    raising an exception if we have a way to deal with this at the
    top level issue of a bush with a context.
Manu Sporny:  Yeah, the disjoint graph solution.
Gregg Kellogg:  It doesn't have to be a disjoint graph, it could
    be a tree. It's not represented as a tree but RDF generated could
    form a tree. Disjoint graph sounds to me like multiple graphs
    like trig. It's a use case I think we've agreed to defer until
    the RDF working group has made up their mind on that.
Manu Sporny:  I don't think we have enough to resolve this issue
    right now. Gregg, throwing an exception is fine for you as long
    as we figure out this top level bush mechanism. You would not
    want to resolve this issue until we resolve that other issue?
Gregg Kellogg:  If we don't resolve the other issue than we are
    in a no man's land. They have to be considered together. Maybe
    would should consider the bush declaration first otherwise we
    could be in a situation where we could not do some forms of
    compaction perhaps.
Manu Sporny:  Ok, I'll shift the agenda around so that we talk
    about graphs, provenance in JSON-LD, and how to express a graph
    and so on.
Niklas Lindström:
    https://github.com/json-ld/json-ld.org/issues/68
Manu Sporny:  Thanks for the discussion. Next week we'll try a
    super session and try to keep doing that until we clear out more
    issues. We started ball rolling on getting JSON-LD into a working
    group and people are ready but now we have many issues.
Niklas Lindström:  When a working group starts on it they might
    change it?
Manu Sporny:  Yeah, we have a much more solid proposal than most,
    and we'll pull people working on this into the working group so
    they can explain the decisions we've made. We're hoping for not
    that much change when going to a working group.
Niklas Lindström:  Perhaps additions but not changes?
Manu Sporny:  You never know what might get thrown in the sausage
    factory during the process.
Niklas Lindström:  I think we're fairly aligned.
Manu Sporny:  I think so.

-- manu

-- 
Manu Sporny (skype: msporny, twitter: manusporny)
Founder/CEO - Digital Bazaar, Inc.
blog: PaySwarm vs. OpenTransact Shootout
http://manu.sporny.org/2011/web-payments-comparison/
Received on Monday, 13 February 2012 13:52:40 GMT

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