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Levels in DGN Libraries

The term "level library" refers to a component of a DGN library that contains a level structure — that is, one or more level definitions. They can be filtered at any time to make only specific levels within a level library available during the design process. New level libraries can be created, and new and existing level libraries can be attached, detached, imported, and exported using the Level Manager dialog.

Note: Level structures are not hierarchical but level library filters are. Level filters are used to combine level definitions into groups.

Attaching and Detaching Level Libraries

The level library's Attach and Detach utility is valuable for setting up seed files. CSV files can be manually attached to drive levels, however they cannot be used in the MS_DGNLIBLIST variable.

When a level is copied from an attached library or from a library specified by the MS_DGNLIBLIST configuration variable, it is considered to be coming from an external source. If a library containing the level is no longer available, either because it is not attached or because it is no longer specified by MS_DGNLIBLIST, "**External**" appears in the level's Library column in the Level Manager dialog. This indicates that the level is a library level and is not subject to certain modifications.

If you update the level, it will no longer be considered as coming from an external source and the **External** designation will be removed. If the level is unused and if MS_UPDATE_KEEP_UNUSED_LIBRARY_LEVELS is not set and you click the Update Levels from Library icon, the level will be deleted.

Note: A level definition does not technically attach from a level library to a DGN file until it is used. This is analogous to attaching a cell from a cell library. After attaching a cell library, the cells are not present in the DGN file until they are placed.

Importing and Exporting Level Libraries

The level library's Import utility is valuable for copying levels from a DGN or CSV file into an active file.

Note: Level files (*.LVL) from previous versions of the product can be imported; however, any previous group structure will not follow.

The level library's Export utility is valuable for creating a new DGN or CSV file containing levels that are defined by individual administrators. After defining and establishing levels and optional level filters, the administrator would export the levels to the users as a project standard. Users would then attach or import the levels. It is recommended that the administrator use the file extension *.dgnlib when exporting a level library. For more information on the mechanics of creating levels and level filters see the Level System.

Administrators can export level libraries as CSV files by selecting Levels > Export in the Level Manager dialog. Once exported, the *.CSV file can be opened in Microsoft Excel where the level definitions can be modified. The modified *.CSV file can then be made available to the users to import into their DGN files.

Furthermore, administrators can achieve ultimate control of level libraries by connecting Microsoft Excel to a database via ODBC, whereby using the database to drive level usage.