# Multi users considerations

BOUML attributes an identifier to the main objects to resolve the references to the not already read objects when you load a project. This identifier is establish during the object creation and will not change later, to allow several users to work simultaneously on the same project, this object identifier contains the identifier of the user creating the object. This explains why BOUML ask you to have an own identifier between 2 and 127 defined through the environment variable BOUML_ID (see Define an environment variable).

These identifiers are also used to name the files memorizing a project, refer to Project files. The plug-out API define the UmlBaseItem::supportFile to know whose file(s) support a given item.

When it loads a project, BOUML check the write permission, in the browser the writable objects are written in bold. When you are several to work on the same project under Linux, a good way is to use the write protection of the files, allowing only one to modify a given file. Even the Project files are Ascii files, I may be difficult to merge several version of the same file.

When you load a project, this one must be consistent, else the references to the unknown items are removed and these unknown items are considered deleted.

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