COLLABORATIVE TEXT EDITOR• Multiple users distributed

geographically can access the same document simultaneously.

• CHARACTERISTICS– high concurrency– hidden latency– consistency

SCOPE• EDITOR– distributed– 1D text only editor

• OPERATIONS– character-wise operation– insert a character– update• delete at index i • insert at index i

SCOPE• Can be shared between any number

of users.• Achieves convergence– Temporary divergence is acceptable.

• Preserves causality of operations

CHALLENGES• NO GLOBAL TIME–Distributed users.

• LATENCY– Latency is never zero.

• DIVERGENCE– Text at multiple site should converge.

SOLUTION• LATENCY– document is replicated– each client/site gets a copy– PROBLEM• consistency issues• all the documents should converge to the same state.

• NO GLOBAL TIME– vector timestamps

TERMINOLOGY• OPERATION– every action by user.– <INDEX, TYPE, CHAR, CID, VECTOR-TIMESTAMP>

ex: document is shared by three clients

CLIENT-1 INSERTS ABC

•<1,i , ‘A’, 1, (1,0,0)>•<2,i , ‘B’, 1, (2,0,0)>•<3,i , ‘C’, 1, (3,0,0)>

TERMINOLOGY

DIVERGENCE• initially documents

are identical

• executing independent operations causes the replicas to diverge

OPERATIONAL TRANSFORMATION• Applying remote operations directly

makes the document inconsistent• Operational Transformation (OT) –

guarantees convergence.

• Initially documents are identical.

• Transform remote operations to ensure convergence of documents.

ARCHITECTURE

ENTITIES

SERVER/CLIENT COMPONENTSSERVER

CLIENTClient maintains client-Id, local cache, History Buffer, site’s vector timestamp.

NEW DOCUMENTCREATE + RETRIEVE

SYNC

TECHNOLOGY STACK• FRONT END–HTML, CSS, JAVASCRIPT–BOOTSTRAP, jQuery, CODE MIRROR

• BACK END– JAVA– JERSEY FRAMEWORK

• COMMUNICATION– JSON

DEMO

REFERENCES• Chengzheng Sun and Clarence Ellis. 1998. Operational

transformation in real-time group editors: issues, algorithms, and achievements. In Proceedings of the 1998 ACM conference on Computer supported cooperative work (CSCW '98). ACM, New York, NY, USA, 59-68. DOI=10.1145/289444.289469 http://doi.acm.org/10.1145/289444.289469

• Chengzheng Sun, Xiaohua Jia, Yanchun Zhang, Yun Yang, and David Chen. 1998. Achieving convergence, causality preservation, and intention preservation in real-time cooperative editing systems. ACM Trans. Comput.-Hum. Interact. 5, 1 (March 1998), 63-108. DOI=10.1145/274444.274447 http://doi.acm.org/10.1145/274444.274447

Thank you!!By

Ambika BabujiMalinipriya Goppannan Ravi

For COMP 512