Limitations of the Data Model

We have described a data model and a distribution model which are oriented towards building a scalable distributed shared text editor. However, the data model and more importantly its distribution model impose a set of limitations on the functionality of the shared editor, or on the way this functionality is implemented.

Whilst a data model based on blocks and lines allows different blocks or lines to be modified simultaneously without any problem, the lock-free distribution model and the choice of a line as ADU mean that it is possible for more two or more users to attempt to modify the same line effectively simultaneously.

In addition, network partitions can result in more complex inconsistencies arising. We shall show below that a few simple choices can result in all such more complex inconsistencies becoming equivalent to a detectable case of effectively simultaneous insertion of lines into the same place, and that this can be resolved as all the alternative information is available at each site.