Essential Database Objects

As objects are created in AutoCAD, they are added to their appropriate container object in the database. Entities are added to the records in the block table. Symbol table records are added to the appropriate symbol tables. All other objects are added to the named object dictionary or to objects that are owned by other objects (and, ultimately, by the named object dictionary), or to an extension dictionary. The scenario in the following section, "Creating Objects in AutoCAD," details this process. Extension dictionaries are discussed in the "Extension Dictionary" section.

To be usable, a database must have at least the following set of objects:

• A set of nine symbol tables that includes the block table, layer table, and linetype table. The block table initially contains three records: a record called *MODEL_SPACE, and two paper space records called *PAPER_SPACE and *PAPER_SPACE0. These block table records represent model space and the two predefined paper space layouts. The layer table initially contains one record, layer 0. The linetype table initially contains the CONTINUOUS linetype.
• A named object dictionary. When a database is created, this dictionary already contains four database dictionaries: the GROUP dictionary, MLINE style dictionary, layout dictionary, and plot style name dictionary. Within the MLINE style dictionary, the STANDARD style is always present.

These objects can be automatically created in a new database by passing kTrue in for the AcDbDatabase constructor's buildDefaultDrawing argument. Passing in kFalse creates an empty database into which a DWG or DXF ^™  file can be loaded.