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Operational Transformation Engine API

About

This project contains the JavaScript source for the operational transformation (OT) engine. The OT engine is exposed as a library for application programmers who wish to build collaborative groupware applications.

The OT API is built using Asynchronous Module Definitions (AMD) so that it can easily be used with any toolkit that supports AMD loading (eg. Dojo). The OT API can also be used with Node.js with the requirejs module for loading the OT library.

Getting started

System requirements

Currently, the OCW OT API supports Unix-like systems with the following tools.

  • JavaScript platform - for running the OT code itself
  • Node.js, npm (optional, for using the OT API with Node.js)
  • sphinx docs (optional, for building documentation)

Getting the code

Application programmers wishing to use the OT API can checkout this project as a git repository (or submodule into an already existing git repository), or download the code as a tarball and extract into their project.

The code is available as a Node.JS module accessible via npm, module name coweb-jsoe.

Development

This section describes how to setup a development environment to for coweb-jsoe development.

Code organization

  • /src The source code lives here.
    • /src/coweb/jsoe coweb-jsoe OT Engine JavaScript source code
    • /src/org/requirejs Contains the i18n requirejs library. See NOTICES.
    • /src/npm Source for Node.JS module.
  • /docs Sphinx documentation.
  • /examples Example code using the OCW OT API.
  • /bin Scripts to build release versions of the OCW OT API.
  • /dist Release versions.

Building

See /bin/README for building release versions of coweb-jsoe.

Usage

Operational Transform

To get started with operational transform, make sure you understand the basics of operational transform. At the very least, read the last paragraph entitled "A final word".

The most important concept to understand is that the API guarantees convergence of local data structures as long as the local application 1) sends remote peers all local operations and 2) honors all remote operations. The details of the operational transform algorithm are hidden entirely from the application developer.

In this library, the two requirements coorespond to the OTEngine.localEvent and OTEngine.removeEvent methods, respectively. To fulfill the requirements, all local data structure changes must call localEvent and send the returned object to all other peers, and all received remote operations must be passed to removeEvent. The transformed operation returned by removeEvent must be applied exactly to the local data structure.

API usage

Each participating peer has its own instance of an operation engine. Each peer maintains its own local copy of the collaborative data (there is no centrally located copy of the data).

The engine is exposed through the use of two primary mechanisms: applying local/remote operations and sending/retrieving engine internal data structures. Each API call returns a data structure (eg. JSON) that should be forwarded to other remote peers exactly as is. Remote peers then send this data structure through another API call, which returns an operation that should be applied to a local copy of the data.

Documentation

To build the docs, change directory to docs/ and run a make html. The documentation relies on Sphinx to build.

A work-in-progress version of the documentation exists online here.

Support

Please report any issues on the GitHub issue tracker.

OpenCoweb

This library was initially started as a part of the OpenCoweb project. OpenCoweb provides a Java-based server and uses cometd techniques to allow remote peer communication and exchange of remote events. OpenCoweb incorporates the OT API to allow developers to write collaborative groupware web-based applications.

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