Collateral Damage U.S. Covert Operations and the Terrorist Attacks on September 11 2001 This page contains general information on the collection and presentation of U.S. Federal Highway Administration Research and Technology Coordinating, Developing, and Delivering Highway Transportation Innovations. Operational transformation - Wikipedia, the free encyclopedia. Operational transformation (OT) is a technology for supporting a range of collaboration functionalities in advanced collaborative software systems. Malaria Prevention: Lessons Learned be carefully evaluated before an intervention method is adopted. Lesson Two: Methodological approaches for assessing. Doing Business in Missouri: Basics is designed to provide information to new or existing business owners on the skills needed to operate a small business and some. 3 Neither will we duplicate the dialog of previous articles that have provided excellent commentary on segments of this same topic. Articles such as the one. OT was originally invented for consistency maintenance and concurrency control in collaborative editing of plain text documents. Two decades of research has extended its capabilities and expanded its applications to include group undo, locking, conflict resolution, operation notification and compression, group- awareness, HTML/XML and tree- structured document editing, collaborative office productivity tools, application- sharing, and collaborative computer- aided media design tools (see OTFAQ). In 2. 00. 9 OT was adopted as a core technique behind the collaboration features in Apache Wave and Google Docs. History. Several years later, some correctness issues were identified and several approaches. In 1. 99. 8, a Special Interest Group on Collaborative Editing (SIGCE) was set up to promote communication and collaboration among CE and OT researchers. Since then, SIGCE holds annual CE workshops in conjunction with major CSCW (Computer Supported Cooperative Work) conferences, such as ACM CSCW, GROUP and ECSCW. System architecture. The shared documents are replicated at the local storage of each collaborating site, so editing operations can be performed at local sites immediately and then propagated to remote sites. Remote editing operations arriving at a local site are typically transformed and then executed. The transformation ensures that application- dependent consistency criteria are achieved across all sites. The lock- free, nonblocking property of OT makes the local response time not sensitive to networking latencies. As a result, OT is particularly suitable for implementing collaboration features such as group editing in the Web/Internet context. The basic idea of OT can be illustrated by using a simple text editing scenario as follows. Given a text document with a string . Suppose the two operations are executed in the order of O1 and O2 (at site 1). After executing O1, the document becomes . To execute O2 after O1, O2 must be transformed against O1 to become: O2' = Delete. However, if O2 is executed without transformation, it incorrectly deletes character . The basic idea of OT is to transform (or adjust) the parameters of an editing operation according to the effects of previously executed concurrent operations so that the transformed operation can achieve the correct effect and maintain document consistency. Consistency models. A number of consistency models have been proposed in the research community, some generally for collaborative editing systems, and some specifically for OT algorithms. The CC model. The causal relationship between two operations is defined formally by Lamport's . When two operations are not causally dependent, they are concurrent. Two concurrent operations can be executed in different order on two different document copies. Convergence: ensures the replicated copies of the shared document be identical at all sites at quiescence (i. Since concurrent operations may be executed in different orders and editing operations are not commutative in general, copies of the document at different sites may diverge (inconsistent). The first OT algorithm was proposed in Ellis and Gibbs's paper. The intention of an operation O is defined as the execution effect which can be achieved by applying O on the document state from which O was generated. The CCI model extends the CC model with a new criterion: intention preservation. The essential difference between convergence and intention preservation is that the former can always be achieved by a serialization protocol, but the latter may not be achieved by any serialization protocol if operations were always executed in their original forms. Achieving the nonserialisable intention preservation property has been a major technical challenge. OT has been found particularly suitable for achieving convergence and intention preservation in collaborative editing systems. The CCI model is independent of document types or data models, operation types, or supporting techniques (OT, multi- versioning, serialization, undo/redo). It was not intended for correctness verification for techniques (e. OT) that are designed for specific data and operation models and for specific applications. The consistency model proposed in these two approaches consist of the following formal conditions: Causality: the same definition as in CC model. Single- operation effects: the effect of executing any operation in any execution state achieves the same effect as in its generation state. Multi- operation effects: the effects relation of any two operations is maintained after they are both executed in any states. The CA model. Effectively, the specification is reduced to new objects introduced by insert operations. However, specification of the total order entails application- specific policies such as those to break insertion ties (i. Consequently, the total order becomes application specific. Moreover, in the algorithm, the total order must be maintained in the transformation functions and control procedure, which increases time/space complexities of the algorithm. Alternatively, the CA model is based on the admissibility theory. All cooperating sites converge in a state in which there is a same set of objects that are in the same order. Moreover, the ordering is effectively determined by the effects of the operations when they are generated. Since the two conditions also impose additional constraints on object ordering, they are actually stronger than convergence. The CA model and the design/prove approach are elaborated in the 2. One established strategy of designing OT systems. The correctness responsibilities of these two layers are formally specified by a set of transformation properties and conditions. Different OT systems with different control algorithms, functions, and communication topologies require maintaining different sets of transformation properties. The separation of an OT system into these two layers allows for the design of generic control algorithms that are applicable to different kinds of application with different data and operation models. The other alternative approach was proposed in. There is no need to enforce a total order of execution for the sake of achieving convergence. Their approach is generally to first identify and prove sufficient conditions for a few transformation functions, and then design a control procedure to ensure those sufficient conditions. This way the control procedure and transformation functions work synergistically to achieve correctness, i. In their approach, there is no need to satisfy transformation properties such as TP2 because it does not require that the (inclusive) transformation functions work in all possible cases. OT data and operation models. Different OT systems may have different data and operation models. For example, the data model of the first OT system. The basic operation model has been extended to include a third primitive operation update to support collaborative Word document processing. A data adaption process is often required to map application- specific data models to an OT- compliant data model. In this approach, the OT operation model is generic, so transformation functions can be reused for different applications. Application- specific operation model approach: which is to devise transformation functions for each pair of application operations. In this approach, transformation functions are application- specific and cannot be reused in different applications. OT functions. OT functions used in different OT systems may be named differently, but they can be classified into two categories: For example, suppose a type String with an operation ins(p, c, sid) where p is the position of insertion, c the character to insert and sid is the identifier of the site that has generated the operation. We can write the following transformation function. T(ins(p. 1,c. 1,sid. The complexity of OT function design is determined by various factors: the functionality of the OT system: whether the OT system supports do (consistency maintenance), undo, locking. These properties can be maintained by either the transformation control algorithm. The specifications of these properties and preconditions of requiring them are given below. Convergence properties. CP1/TP1 precondition: CP1/TP1 is required only if the OT system allows any two operations to be executed in different orders. CP2/TP2: For every three concurrent operations op. CP2/TP2 stipulates equality between two operations transformed with regard to two equivalent sequences of operations: the transformation of op. CP2/TP2 precondition: CP2/TP2 is required only if the OT systems allows two operations op. They are: IP1: Given any document state S and the sequence op. This property is required in an OT system for achieving the correct undo effect, but is not related to IT functions. IP2: The property IP2 expresses that the sequence op. The transformation functions satisfy IP2 if and only if: T(opx,op. IP2 precondition: IP2 is required only if the OT systems allows an operation opx. The transformation functions satisfy the property IP3 if and only if op. IP3 precondition: IP3 is required only if the OT system allows an inverse operation op. The complexity of OT control algorithm design is determined by multiple factors. A key differentiating factor is whether an algorithm is capable of supporting concurrency control (do) and/or group undo. However, it was well known that concurrency condition alone cannot capture all OT transformation conditions. Their approaches differ from those listed in the table. They use vector timestamps for causality preservation. The other correctness conditions are . Those conditions are ensured by the control procedure and transformation functions synergistically. There is no need to discuss TP1/TP2 in their work.
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