Re: [office-collab] Additional use case for change tracking (MCT Solution)

[Svante Schubert <svante.schubert@gmail.com>]

Here the MCT representations of the two cases that Patrick proposed.
Please excuse the delay, I had been working on an MCT prototype based on the Apache (Incubating) ODF Toolkit and had been distracted from this task.

CASE 1
1. Original saved by 1st author
<text:p>This is the original paragraph, created with change tracking on so seen as an added paragraph.</text:p>

2. 2nd author changes text:
<text:p>This is the second version of the paragraph, created with change tracking on so seen as a modifed paragraph.</text:p>

<text:p>This is the original paragraph, created with change tracking on so seen as a paragraph.</text:p>


// FILEPATH "./content.xml"
// DESCRIPTION:  The following is part of a content.xml file, similar abbreviated as Robin did before

<xmlns:text="urn:oasis:names:tc:opendocument:xmlns:text:1.0" xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0">
    <!-- ... -->
    <office:text >
        <text:p>This is the second version of the paragraph, created with change tracking on so seen as a modifed paragraph.</text:p>
    </office:text>
    <!-- ... -->


// FILEPATH "./meta.xml"
// DESCRIPTION:  Store all metadata of changes in the metadata file.

<office:document-meta office:version="1.3"
    xmlns:meta="urn:oasis:names:tc:opendocument:xmlns:meta:1.0"
    xmlns:office="urn:oasis:names:tc:opendocument:xmlns:office:1.0"
    xmlns:dc="http://purl.org/dc/elements/1.1/">
    <office:meta>
        <meta:generator>ODFApp/1.0$Win32/123m1$Build-007</meta:generator>
        <meta:creation-date>20120618T145700+0100</meta:creation-date>
        <meta:initial-creator xml:id="User1">1st author</meta:initial-creator>
        <dc:creator xml:id="User2">2nd author</dc:creator>
        <dc:date>20120618T145922+0100</dc:date><!-- time of change the ODF XML is related to -->
        <dc:language>en-US</dc:language>
        <meta:editing-cycles>2</meta:editing-cycles>
    <office:meta>
</office:document-meta>

 
// FILEPATH "./changes/undo.xml"
// DESCRIPTION:  Undo change operations are being stored in this file. The directory is useful for keeping changed binary data

<undo xmlns="http://docs.oasis-open.org/ns/office/1.3/merge/ct#" meta-file="../meta.xml">
    <add type="text" time="23s"        by="User1" s="/1/1">This is the original paragraph, created with change tracking on so seen as an added paragraph.</add>
    <del type="text" time="1m58s"  by="User2" s="/1/12" e="/1/20"/>
    <add type="text" time="2m01s"  by="User2" s="/1/12">second version of the</add>
    <del type="text" time="2m17s"  by="User2" s="/1/89" e="/1/96" />
    <add type="text" time="2m22s"  by="User2" s="/1/89">modified</add>
</undo>


The creation time is of the time, when the empty document is being loaded. All following editing operations are relative to this origin time.
The various users/editors are written in the meta.xml and referenced by the undo.xml file.
The start and end parameter of each operation is relative to state of the content.xml just before the operations occurs.

The problem of (real-time) collaboration is similar to the problem of the shell game (or thimblerig). In a shell game you have one marble under several shells and you have to take track of the shell with the marble.
In collaboration others are changing the content and someone has to take track of the own changes.
This magic of the solution is enabled by operations and their relative references, but is happening during run-time and is hidden from the specification. It is called Operational Transformation (OT) [1][2][3].
Basically OT is about adapting the existing operations to compensate the influence of other users. For instance, incrementing the reference, if a component was inserted before. For example, if you work on the third paragraph and someone is inserting a new second parameter, you still want to work on the same paragraph, but it is no longer the third, but the forth..

PS: The second example will be answered tomorrow, I will have to focus on the soccer game..

[1] http://en.wikipedia.org/wiki/Operational_transformation
[2] http://www.heise.de/developer/artikel/Synchronisationsalgorithmen-verstehen-1562877.html?artikelseite=1 (German - e.g. use Chrome browser context menu to translate)
[3] http://www.codecommit.com/blog/java/understanding-and-applying-operational-transformation