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From Michael MacFadden <>
Subject Re: Future of Apache wave [Was: Re: Advantages of P2P messaging?]
Date Fri, 14 Jun 2013 08:39:21 GMT
Bruno / Sam,

This is the tricky part.  You can abstract "some" parts of the operation
but not all.  The whole point of the OT Stack is to adjust the parameters
of you operations so that they have the same meaning in multiple contexts.
 We can't abstract away all of those parameters because the transformation
functions must define rules to transform those parameters.

That said, in an object oriented language you typically have two types of
entities.  Object Types and Primitive Types.  You may need operations than
handle both.  For example, the things you may do to an int, may be
different than what you would do with a "Person" object.  The things you
do with an Array may be different than that things you do with a Map.

Correctly defining this set of operations is tricky and, as I said, part
of ongoing research.  But the approach is sound from an idealistic
standpoint.  Whether it is practical or not is another story.


On 6/13/13 9:15 PM, "Bruno Gonzalez (aka stenyak)" <>

>I assume the "path" or "index" would be abstracted too. This way, OT can
>also handle the (x,y) position of a pixel in an image, or any other kind
>position or range in which the operation must be applied.
>On Thu, Jun 13, 2013 at 10:06 PM, Sam Nelson <> wrote:
>> Hi Michael,
>> I'm trying to wrap my head around this too.
>> Say you have some JSON object:
>> {
>>   "i" : 5
>>   "s" : "string"
>>   "c" : { "i" : 2 }
>>   "a" : [ { "i" : 3 } ]
>> }
>> What would the parameters be to delete "s" since a path is really
>> isn't it, rather than an index? (i.e. parameters are specific to the
>> they operate on)  And further, what would a delete operation do in this
>> case?  remove the "s" member of the object, or just set its value to
>>  That decision could be application implementation specific, sure, but
>> the application needed both concepts, how can you now define two
>> delete operations, in order for the application to implement them both
>> each case?
>> -Sam
>> On 14/06/2013 07:45, Michael MacFadden wrote:
>>> Joseph,
>>> We are almost in sync now.  Lets go one step further.  Let's so you
>>> designing an application to be a rich text editor.  Forget OT, you just
>>> making an editor.  I assume your editor has to have some sort of model
>>> right?  Let's temporarily forget the persistence format.  You may save
>>> rich text to xml, or rtf, or whatever, but I am not worried about
>>>that.  I
>>> am saying what is the in memory model that your editor uses to interact
>>> with the document?  Build that.  Build it any way you like.
>>> Ok so now you have a rich text object model.  Your editor is going to
>>> interact with that though some sort of object model API.  When the user
>>> selects some text and presses the bold button, the editor makes some
>>> call to the model and says, make this part bold.  For the sake of
>>> conversation, I don't care how that internally happens in the object
>>> model.
>>> OK.  So now if we have a sufficiently powerful OT operation set can
>>> describe manipulating objects, we can manipulate the object model with
>>>   Really what OT services are, are robust message busses that describe
>>> one user is changing the objects to another user, and accounting for
>>> context transformations along the way.  So if you can build an
>>>abstract OT
>>> operation set that lets you mess with objects and objects structures,
>>> you have a shot at then adapting that operation set to a whole slew of
>>> applications.
>>> This is actually an ongoing area of research, that I presented a paper
>>> to the collaborative editing workshop at the ACM CSCW conference last
>>> year.
>>> ~Michael
>>> On 6/13/13 8:34 PM, "Joseph Gentle" <> wrote:
>>>  Interesting...
>>>> The abstraction I use is to have a bunch of data types. Each data type
>>>> defines what documents look like, what operations look like and they
>>>> define a set of OT functions (transform, compose, apply, etc). Eg,
>>>> Text documents are strings and their operations are lists of {skip:5},
>>>> {insert:'hi'}, {delete:10}, etc. JSON documents are JSON and their
>>>> operations are lists of path+what to do there. Eg, [{path: ['hi'],
>>>> delete list element 5}, ...]
>>>> It sounds like you're saying we should abstract over the ideas of
>>>> ot-for-lists, ot-for-sets and so on. Is that right?
>>>> ... But rich text isn't quite a list or a set. You can make annotation
>>>> markers or something, but then they take up space. Maybe its possible
>>>> to ignore the final document space that an annotation takes up for the
>>>> purpose of transformation?
>>>> Another architecture I've thought about using is making all documents
>>>> use the JSON OT code. Specialized type like rich text can exist as
>>>> leaves in the JSON structure - and let you embed a rich text operation
>>>> inside a JSON operation.
>>>> -J
>>>> On Thu, Jun 13, 2013 at 12:05 PM, Michael MacFadden
>>>> <> wrote:
>>>>> As a follow up.  The reason you are struggling with the concept is
>>>>> you have tied the operation language directly to a specific data
>>>>> in
>>>>> much the way wave did.  They created a conversation model and a
>>>>> set of operations that act on that model.  When you do that your
>>>>> operations a making assumptions on how the object model works.  This
>>>>> coupling is not a good idea.  Much of the OT community strongly
>>>>> recommends
>>>>> avoiding this.
>>>>> Rather great a generic set of operations that manipulate things in an
>>>>> abstract way, and then let the application sort out what to do with
>>>>> operations when it receives it.  The OT stack only needs to
>>>>> how
>>>>> the parameters of the operations interact; such as positional
>>>>> for insert and delete style operations.  The OT Stack doesn't need to
>>>>> know
>>>>> that the thing you are inserting is a character, a contact card, a
>>>>> database record, or an object in a list.  It doesn't care.  It just
>>>>> knows
>>>>> that if one insert happens before another it has to increment the
>>>>> of
>>>>> the second operation.
>>>>> If things are decoupled in this way, the whole OT stack becomes much
>>>>> more
>>>>> flexible.  As one of the founders of OT says almost every time I see
>>>>> him,
>>>>> "Let OT focus on what it is good at, and let it ignore everything
>>>>> ~Michael
>>>>> On 6/13/13 7:54 PM, "Joseph Gentle" <> wrote:
>>>>>  So you're imagining storing rich text like this?
>>>>>> {doc: 'hi there!', annotations: [{from:0, to:2, bold:true}]} or
>>>>>> something?
>>>>>> Every change to the document is going to need to manually update
>>>>>> single annotation which has start / end points after the edit. But
>>>>>> wouldn't work - if you insert some text and I edit an annotation
>>>>>> in the document, my annotation will float forwards / backwards when
>>>>>> get your op because I don't know how I should change it.
>>>>>> This idea comes up about every 6 months on the sharejs mailing list.
>>>>>> Several solutions have been proposed, but none of them work
>>>>>> I think we just need a separate set of transform / apply / ...
>>>>>> functions for rich text.
>>>>>> -J
>>>>>> On Thu, Jun 13, 2013 at 1:19 AM, Michael MacFadden
>>>>>> <> wrote:
>>>>>>> Joseph,
>>>>>>> I disagree.  The annotations themselves are just another data
>>>>>>> structure.
>>>>>>> You add them, remove them and modify them like anything else.
>>>>>>> manage annotations as another structure within the blip model.
>>>>>>> is
>>>>>>> no reason why you can interface them though a JSON Style operations
>>>>>>> structure.
>>>>>>> ~Michael
>>>>>>> On 6/13/13 12:11 AM, "Joseph Gentle" <>
>>>>>>>  The conversation *model* yes, but not the rich text documents
>>>>>>>> themselves. You can't really make text annotations work properly
>>>>>>>> top of JSON operations. We should keep something like the
>>>>>>>> system for actual blips.
>>>>>>>> -J
>>>>>>>> On Wed, Jun 12, 2013 at 4:06 PM, Michael MacFadden
>>>>>>>> <> wrote:
>>>>>>>>> Actually I just went and took a look at your operations.
>>>>>>>>> OT
>>>>>>>>> type
>>>>>>>>> is probably the closest to what I would suggest we use.
>>>>>>>>> Objects
>>>>>>>>> are
>>>>>>>>> not just for javascript.  They define arbitrary objects
>>>>>>>>> We
>>>>>>>>> don't need a specific wave XML type, we could use the
>>>>>>>>> operations
>>>>>>>>> to
>>>>>>>>> modify the conversation model
>>>>>>>>> Potentially.
>>>>>>>>> On 6/12/13 10:55 PM, "Joseph Gentle" <>
>>>>>>>>>  Really?
>>>>>>>>>> My method for ShareJS was to simply have a JSON OT
type and a
>>>>>>>>>> plaintext OT type. I'd like to add a rich text OT
type as well.
>>>>>>>>>> Then
>>>>>>>>>> people can just pick which one based on what kind
of data they
>>>>>>>>>> have.
>>>>>>>>>> For Wave I'd like to be able to do something similar
- JSON is
>>>>>>>>>> obviously useful for storing application data. It'd
be nice to
>>>>>>>>>> some sort of hybrid for wavelets where we can put
>>>>>>>>>> different
>>>>>>>>>> kinds of data inside a wavelet. One option is to
use a JSON OT
>>>>>>>>>> as
>>>>>>>>>> the root of all wavelets and support subdocuments
at arbitrary
>>>>>>>>>> paths
>>>>>>>>>> (so the object could be:
>>>>>>>>>> {projectName:"ruby on rails", files:[{name:'foo/bar.rb',
>>>>>>>>>> documentation:{_type:richtext, _data:"<Rich text
>>>>>>>>>> Or wavelets could simply each have a type (defaulting
to the
>>>>>>>>>> current
>>>>>>>>>> wavey XML type).
>>>>>>>>>> -J
>>>>>>>>>> On Wed, Jun 12, 2013 at 2:41 PM, Michael MacFadden
>>>>>>>>>> <> wrote:
>>>>>>>>>>> You have stumbled upon one of the weaknesses
of wave OT.  Best
>>>>>>>>>>> practices
>>>>>>>>>>> would say to NOT bind your OT directly to the
data type,
>>>>>>>>>>> then
>>>>>>>>>>> you
>>>>>>>>>>> don't have an extendable model. For example if
you have all of
>>>>>>>>>>> your
>>>>>>>>>>> operations figured out and validated, and then
you need to
>>>>>>>>>>> your
>>>>>>>>>>> data model, you have to go back and mess with
>>>>>>>>>>> functions.  Not good.  Or you have to try to
bend new data
>>>>>>>>>>> in
>>>>>>>>>>> to
>>>>>>>>>>> the existing one, also not good.
>>>>>>>>>>> Best practice is to create a generic OT model
and operate on
>>>>>>>>>>> There
>>>>>>>>>>> is debate as to what the model should be, but
most agree on the
>>>>>>>>>>> concept.
>>>>>>>>>>> For example in wave they tried to create a map
like collection
>>>>>>>>>>> that
>>>>>>>>>>> OT
>>>>>>>>>>> could operate on. Essentially though that had
to implement the
>>>>>>>>>>> as
>>>>>>>>>>> if
>>>>>>>>>>> its underlying model was a bunch of XMLish type
tags.  This we
>>>>>>>>>>> very
>>>>>>>>>>> convoluted.
>>>>>>>>>>> ~Michael
>>>>>>>>>>> On 6/12/13 10:26 PM, "Joseph Gentle" <>
>>>>>>>>>>>  Yeah exactly. The google wave OT code uses special
>>>>>>>>>>>> that
>>>>>>>>>>>> can
>>>>>>>>>>>> understand the XML structure. It doesn't
just edit the
>>>>>>>>>>>> Formatting annotations are stored in a special
way -
>>>>>>>>>>>> can
>>>>>>>>>>>> say something like "At position 10 add bold.
At position 20
>>>>>>>>>>>> adding bold".
>>>>>>>>>>>> -J
>>>>>>>>>>>> On Wed, Jun 12, 2013 at 1:56 PM, Bruno Gonzalez
(aka stenyak)
>>>>>>>>>>>> <> wrote:
>>>>>>>>>>>>> I suspected something like that. I assume
it also correctly
>>>>>>>>>>>>> handles
>>>>>>>>>>>>> variable-length UTF8 characters, so it's
not necessarily
>>>>>>>>>>>>> patches?
>>>>>>>>>>>>> This starts to make sense. OT can only
compute conflict-free
>>>>>>>>>>>>> merges
>>>>>>>>>>>>> using
>>>>>>>>>>>>> the "character" primitive (because that's
how Wave was
>>>>>>>>>>>>> originally
>>>>>>>>>>>>> designed). As an unfortunate consequence,
you can then only
>>>>>>>>>>>>> OT-operate
>>>>>>>>>>>>> on
>>>>>>>>>>>>> plain text. Otherwise you could get conflict-free
xml text
>>>>>>>>>>>>> <loo<ks
>>>>>>>>>>>>> li<>ke>this>, and that of
course isn't legal xml.
>>>>>>>>>>>>> But we still want rich text in Google
Wave, therefore all the
>>>>>>>>>>>>> formatting
>>>>>>>>>>>>> stuff is stored some place else, specifically
in the blip
>>>>>>>>>>>>> annotations.
>>>>>>>>>>>>> The
>>>>>>>>>>>>> modifications to annotations are (sometimes)
simply derived
>>>>>>>>>>>>> the
>>>>>>>>>>>>> transformations that the plain text suffers
after merges?
>>>>>>>>>>>>> I suppose there could be other OT algorithms
that don't use a
>>>>>>>>>>>>> "character"
>>>>>>>>>>>>> primitive, but rather an "xml tag" primitive,
a json item, a
>>>>>>>>>>>>> "pixel",
>>>>>>>>>>>>> or
>>>>>>>>>>>>> anything else, right?
>>>>>>>>>>>>> (sorry for only contributing with questions...
>>>>>>>>>>>>> On Wed, Jun 12, 2013 at 10:27 PM, Joseph
>>>>>>>>>>>>> <>
>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>  On Wed, Jun 12, 2013 at 12:13 PM, Bruno
Gonzalez (aka
>>>>>>>>>>>>>> <> wrote:
>>>>>>>>>>>>>>> My assumption was that conflicts
were simply mathematically
>>>>>>>>>>>>>> inevitable
>>>>>>>>>>>>>> in a
>>>>>>>>>>>>>>> DVCSs, that's why your mention
about lack of conflict
>>>>>>>>>>>>>> sparked my
>>>>>>>>>>>>>>> interest... you mention conflicts
like they can be
>>>>>>>>>>>>>> If
>>>>>>>>>>>>>> so,
>>>>>>>>>>>>>> are
>>>>>>>>>>>>>>> conflicts "eliminated" by choosing
an arbitrary merging
>>>>>>>>>>>>>> strategy
>>>>>>>>>>>>>> when
>>>>>>>>>>>>>>> conflicts *do* happen (e.g. "choose
the last timestamped
>>>>>>>>>>>>>> patch
>>>>>>>>>>>>>> and
>>>>>>>>>>>>>> lose
>>>>>>>>>>>>>>> information on the way, we don't
care"), or can they be
>>>>>>>>>>>>>> prevented
>>>>>>>>>>>>>> from
>>>>>>>>>>>>>> ever
>>>>>>>>>>>>>>> happening in the first place?
>>>>>>>>>>>>>> They're inevitable in patch based
systems because patches
>>>>>>>>>>>>>> usually
>>>>>>>>>>>>>> have
>>>>>>>>>>>>>> a line level granularity. OT usually
uses individual
>>>>>>>>>>>>>> positions. In OT, if two operations
both delete the same
>>>>>>>>>>>>>> character,
>>>>>>>>>>>>>> the character gets deleted once.
If two clients insert a
>>>>>>>>>>>>>> character
>>>>>>>>>>>>>> at
>>>>>>>>>>>>>> the same position, one of the characters
will be first in
>>>>>>>>>>>>>> resultant document and one will be
second. Conflict markers
>>>>>>>>>>>>>> just
>>>>>>>>>>>>>> aren't necessary.
>>>>>>>>>>>>>> -J
>>>>>>>>>>>>>>  --
>>>>>>>>>>>>>>> Saludos,
>>>>>>>>>>>>>>>       Bruno González
>>>>>>>>>>>>>>> ______________________________**_________________
>>>>>>>>>>>>>>> Jabber: stenyak AT
>>>>>>>>>>>>> --
>>>>>>>>>>>>> Saludos,
>>>>>>>>>>>>>       Bruno González
>>>>>>>>>>>>> ______________________________**_________________
>>>>>>>>>>>>> Jabber: stenyak AT
>     Bruno González
>Jabber: stenyak AT

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