A collaborative editor is a form of collaborative software application that allows several people to edit a computer file using different computers. There are two types of collaborative editing: real-time and non-real-time. In Real-time collaborative editing (RTCE), users can edit the same file simultaneously, where as in Non-real-time collaborative editing, the users do not edit the same file at the same time. (similar to revision control systems). Collaborative real-time editors generally permit both the above modes of editing in any given instance.
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The first instance of a collaborative real-time text editor was demonstrated by Douglas Engelbart in 1968, in The Mother of All Demos. Actual implementations of the concept took several decades to appear.
Instant Update was released for Mac OS in 1991 from ON Technology.[1] Later, a version for Microsoft Windows was released as well, allowing real-time collaboration across these two operating systems. Instant Update relied on a work group server to coordinate documents updated in real time on multiple clients.
More recently, SubEthaEdit is Mac-based, and leverages the Mac Bonjour communications platform. SubEthaEdit won numerous awards, and was initially offered free of charge. But later it became commercial because there were not enough voluntary donations to keep it free. The Gobby collaborative editor aims to be very similar to SubEthaEdit, and is cross-platform and open source.
The Web 2.0 phenomenon has caused an explosion of interest in browser-based document editing tools. In particular, a product called Writely saw explosive user growth and was bought by Google in March 2006 (now called Google Docs & Spreadsheets). It provides simultaneous edits on the entirety of a document, though changes from other users are only reflected after the client program polling the server (every half-minute or so). Another early web-based solution was JotSpotLive, in which line-by-line simultaneous editing was available in near-realtime.[2] However, after Google's purchase of parent company JotSpot in November 2006, the site was closed. Google Sites was launched in February 2007 as a refactoring of JotSpot,[3][4][5][6] but it lacks the multi-user real-time abilities of JotLive. The Synchroedit (rich text) and MobWrite (plain text) projects have since emerged as two open-source attempts to fill the in gap real-time browser-based collaborative editing, though still unable to achieve true real-time performance, especially on a large scale architecture. EtherPad was the first web editor to provide a smooth, character-by-character real-time performance, something that previously was only available in desktop editors.
In 2009, Google started beta testing Google Wave, a real-time collaboration environment which Google hoped would eventually displace email and instant messaging. EtherPad was subsequently acquired by Google, which allocated the EtherPad team to work within the Wave project. However, Google announced in August 2010 on its blog[7] that it had decided to stop developing Wave as a standalone project, due to insufficient user adoption.
The complexity of real-time collaborative editing solutions stems from communication lag. In theory, if communication were instantaneous, then creating a real-time collaborative editor would be no more difficult than creating a single-user editor, because a document could be edited using an algorithm similar to the following:
However, the speed of communication is limited by network lag. This creates a fundamental dilemma: users need their own edits incorporated into the document instantly, but if they are incorporated instantly, then because of communication lag, their edits must necessarily be inserted into different versions of the document.
An example illustrates this problem. Suppose Bob and Alice start with a document containing the word Mary. Bob deletes 'M', then inserts 'H', to change the word into Hary. Alice, before she receives either edit from Bob, deletes 'r', then deletes 'a', to change it into My. Both Bob and Alice will then receive edits that were applied to versions of the document that never existed on their own machines.
Thus, the challenge of real-time collaborative editing is to figure out exactly how to apply edits from remote users, which were originally created in versions of the document that never existed locally, and which may conflict with the user's own local edits.[8]
The most sophisticated solutions solve this problem in a way that does not require a server, does not use locking (all users can freely edit all parts of a document at the same time), and supports any number of users (limited only by the resources of the computers). UNA and SubEthaEdit are examples of two programs that take this approach.
While these sophisticated approaches enable the best user experience, a basic collaborative editor can also be created in a client–server model. In a client–server scenario, one of the editor instances is assigned the role of collaboration server when the document is opened. This server ensures that other editors are kept in sync by determining network latency and acting as a time synchronization server. The server receives timestamped notifications of changes made to the document by other users. It determines how those changes should affect its local copy, and broadcasts its changes to the collaboration pool. In some models, the changes are not reflected on a client until an official response is returned from the server, even if those changes were made locally.
This approach, while significantly less powerful, allows for basic collaboration at a relatively low cost. This makes it preferable in situations where processing resources are limited, such as on Apple's iPhone platform. NetSketch is an example of a program that uses this model.
In the past, Microsoft and IBM have worked to add collaboration facilities to their existing architectures.[9] Although marketed as real-time collaboration, these 'workspace' approaches require either document locking (so only one person can edit it at a time), or 'reconciliation' of conflicting changes, which is generally found by users to be unsatisfactory.
With advances in internet capacity, collaborative video editing is also becoming mainstream. Collaborative TV production is possible, in which the directors, producers and editors, all of whom contribute to the post-production process, are able to work together remotely. Web-based non-linear editing systems allow collaborative editing of video, similar to the way in which collaborative text editors have worked for text. See Comparison of video editing software and Real-time video editing.
The increasing popularity of WiFi enabled mobile devices, such as Apple's iPhone, has also driven the development of collaborative tools. While simplistic in comparison to real-time video editing software, these applications allow users of mobile devices to create and edit documents over the wireless network. NetSketch was the first collaborative application for the iPhone, and focused on real-time collaborative drawing.[10]
Relevant documents include: