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ACE (editor)
Encyclopedia
ACE - a collaborative editor is a platform-independent, collaborative real-time editor. It is a real-time cooperative editing system that allows multiple geographically dispersed users to view and edit a shared text document
at the same time.
with standard features such as copy/paste and load/save. Multiple documents can be edited at the same time. Furthermore, ACE can share documents with other users on different computers, connected by communication networks (LAN
, Internet
). ACE also discovers users and their shared documents automatically in a local area network. Users can opt to join any discovered shared document. For all this, no configuration is necessary because it is based on zero-conf networking.
Once a user has joined a shared document, he can freely edit the document at the same time with all participants as a virtual team. So-called awareness information helps to avoid unnecessary conflicts (that is, two users editing at the same time and text location). Awareness information includes the cursor and the currently selected text of the other users marked with the color of the respective user.
The heart of the application is a concurrency control algorithm based on the innovative concept of operational transformation
, which allows for lock-free editing of a document by multiple users. It imposes no editing constraints and resolves all conflicts automatically. The algorithm overcomes one of the most significant challenges in designing and implementing real-time collaborative editing systems, namely consistency preservation. That is to ensure that at quiescence (that is, when no messages are in transit) the shared document is identical for all participants.
ACE builds upon open technologies such as BEEP
(RFC 3080) and zero-conf networking. All this leaves the possibility open to communicate even with different applications that understand the public protocol of ACE.
ACE runs on all major operating systems such as Windows
, Mac OS X
or Linux
and is free software
.
OS, whereas Scott uses Mac OS X
and Sam Linux
OS. Note that the blue color always denotes the text written by the local user of the ACE instance. The color to matching a participant is depicted in the participants view of the GUI
.
The last point reveals some more potential for cooperative editing systems: Groups of two to three students can write essays together. On the one hand, they teach each other how to use the written language, and on the other hand, they can have fun together using a hands-on application on the computer, thus losing fear of contact with the computer, which is essential in today's education.
The following requirements have been identified for such systems:
A real-time cooperative editing system consists of n instances, each instance run by a different user. All instances are connected by a network. One of the most significant challenges in designing and implementing real-time cooperative editing systems is consistency maintenance among the different document replicas (one for each site). A cooperative editing system is said to be consistent if it always maintains the following properties:
One solution to achieve consistency control is provided by Operational Transformation
(OT) algorithms. The OT algorithm approach consists of two main components:
The theory on consistency maintenance stems from the research field called Computer Supported Cooperative Work
, for short CSCW.
Document
The term document has multiple meanings in ordinary language and in scholarship. WordNet 3.1. lists four meanings :* document, written document, papers...
at the same time.
Introduction
ACE is a simple text editorText editor
A text editor is a type of program used for editing plain text files.Text editors are often provided with operating systems or software development packages, and can be used to change configuration files and programming language source code....
with standard features such as copy/paste and load/save. Multiple documents can be edited at the same time. Furthermore, ACE can share documents with other users on different computers, connected by communication networks (LAN
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....
, Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
). ACE also discovers users and their shared documents automatically in a local area network. Users can opt to join any discovered shared document. For all this, no configuration is necessary because it is based on zero-conf networking.
Once a user has joined a shared document, he can freely edit the document at the same time with all participants as a virtual team. So-called awareness information helps to avoid unnecessary conflicts (that is, two users editing at the same time and text location). Awareness information includes the cursor and the currently selected text of the other users marked with the color of the respective user.
The heart of the application is a concurrency control algorithm based on the innovative concept of operational transformation
Operational transformation
Operational transformation is a technology for supporting a range of collaboration functionalities in advanced groupware systems. OT was originally invented for consistency maintenance and concurrency control in collaborative editing of plain text documents...
, which allows for lock-free editing of a document by multiple users. It imposes no editing constraints and resolves all conflicts automatically. The algorithm overcomes one of the most significant challenges in designing and implementing real-time collaborative editing systems, namely consistency preservation. That is to ensure that at quiescence (that is, when no messages are in transit) the shared document is identical for all participants.
ACE builds upon open technologies such as BEEP
BEEP
In computer networking, BEEP is a framework for creating network application protocols. It includes an application protocol kernel for connection-oriented asynchronous interactions, and can be used both for binary and text messages within the context of a single application user identity.BEEP is...
(RFC 3080) and zero-conf networking. All this leaves the possibility open to communicate even with different applications that understand the public protocol of ACE.
ACE runs on all major operating systems such as Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
or Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
and is free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
.
Example Use Case
Consider a collaborative editing session with three participants, named Bill, Steve and Scott, as depicted by the figure. There is also a fourth user, named Sam, who does not participate in the session. The document which the users collaboratively edit is Collaboration.txt. User Scott is the owner and publisher of it. Note that users Steve and Bill work on Microsoft WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
OS, whereas Scott uses Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
and Sam Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
OS. Note that the blue color always denotes the text written by the local user of the ACE instance. The color to matching a participant is depicted in the participants view of the GUI
Gui
Gui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
.
Usage
Here is a list with a few examples on how ACE can be used:- group brainstorming
- source code development (XPExtreme ProgrammingExtreme programming is a software development methodology which is intended to improve software quality and responsiveness to changing customer requirements...
) - collective note-taking
- Write texts together (e-mails, letters, journals, etc.)
- educational purposes
The last point reveals some more potential for cooperative editing systems: Groups of two to three students can write essays together. On the one hand, they teach each other how to use the written language, and on the other hand, they can have fun together using a hands-on application on the computer, thus losing fear of contact with the computer, which is essential in today's education.
Technology background
A real-time cooperative editing system such as ACE allows multiple users to view and edit the same document at the same time from multiple geographically dispersed sites. The sites are connected by communication networks.The following requirements have been identified for such systems:
- Real-timeReal-time computingIn computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
: The response to local user actions must be quick, ideally as quick as a single user editor, and the latencyLatency (engineering)Latency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
for reflecting remote user actions is low (determined by external communication latency only). - Distributed: Cooperating users may reside on different machines connected by communication networks with nondeterministic latency.
- Unconstrained: Multiple users are allowed to concurrently and independently edit any part of the document at any time, in order to facilitate free and natural information flow among multiple users.
A real-time cooperative editing system consists of n instances, each instance run by a different user. All instances are connected by a network. One of the most significant challenges in designing and implementing real-time cooperative editing systems is consistency maintenance among the different document replicas (one for each site). A cooperative editing system is said to be consistent if it always maintains the following properties:
- Convergence: Guarantees when the same set of operations (for example, an operation can be an insert/delete of a character) have been executed at all sites, that all copies (also known as replicas) of the shared document are identical. That is, this property ensures the consistency of the final results at the end of a cooperative editing session.
- Causality-preservation: For any pair of operations Oa and Ob, if Oa -> Ob (that is, Ob is dependent on Oa), then Oa is executed before Ob at all sites. That is, this property ensures the consistency of the execution orders at all sites of dependent operations during a cooperative editing session.
- Intention-preservation: For any operation O, the effects of executing O at all sites are the same as the intention of O, and the effect of executing O does not change the effects of independent operations. That is, this property ensures that executing an operation at remote sites achieves the same effect as executing this operation at the local site at the time of its generation, and the execution effects of independent operations do not interfere with each other.
One solution to achieve consistency control is provided by Operational Transformation
Operational transformation
Operational transformation is a technology for supporting a range of collaboration functionalities in advanced groupware systems. OT was originally invented for consistency maintenance and concurrency control in collaborative editing of plain text documents...
(OT) algorithms. The OT algorithm approach consists of two main components:
- The integration algorithm which is responsible of receiving, broadcasting and executing operations. It is independent of the type of document replica and application.
- The transformation function is responsible for merging two concurrent operations. It is application dependent. For example, a text editor has different operations than a whiteboard application.
The theory on consistency maintenance stems from the research field called Computer Supported Cooperative Work
Computer supported cooperative work
The term computer-supported cooperative work was first coined by Irene Greif and Paul M. Cashman in 1984, at a workshop attended by individuals interested in using technology to support people in their work. At about this same time, in 1987 Dr...
, for short CSCW.
See also
- Collaborative real-time editor
- SubEthaEditSubEthaEditSubEthaEdit is a collaborative real-time editor designed for Mac OS X. The name comes from the Sub-Etha communication network in The Hitchhiker's Guide to the Galaxy series....
- GobbyGobbyGobby is a free software collaborative real-time editor available on Windows and Unix-like platforms. It was initially released in June 2005 by the 0x539 dev group....
- Computer Supported Collaborative Work
External links
- ACE Website - the official website of ACE