Rules for working with schema locks

A schema is the structure or design of a database or database object such as a feature class or table. A schema lock means that another application is accessing a database, and you are not allowed to alter its structure by adding or removing fields. The most common cause for a schema lock is displaying a dataset in ArcMap.

There are four rules that summarize the behavior of geoprocessing tools and scripts when using data that may also be accessed simultaneously by other applications.