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Database Objects<br />
AutoCAD ® drawings consist largely of structured containers for database<br />
objects. Database objects each have the following:<br />
■ Handle whose value is unique to the drawing/DXF file, and is constant for<br />
the lifetime of the drawing. This format has existed since AutoCAD<br />
Release 10, but as of AutoCAD Release 13, handles are always enabled.<br />
■ Optional xdata table, just as entities have had since AutoCAD Release 11.<br />
■ Optional persistent reactor table.<br />
■ Optional ownership pointer to an extension dictionary, which in turn<br />
owns subobjects placed in it by an application.<br />
Symbol tables and symbol table records are database objects and, thus, have<br />
a handle. They can also have xdata and persistent reactors in their DXF<br />
records.<br />
Persistent Inter-Object Reference Handles<br />
A set of group code ranges permit objects to directly specify references to<br />
other objects within the same drawing/DXF file. Four ranges are provided for<br />
the four types of reference handles that you can specify:<br />
■<br />
■<br />
■<br />
■<br />
Soft-pointer handle<br />
Hard-pointer handle<br />
Soft-owner handle<br />
Hard-owner handle<br />
These handle types are manifested as entity names in AutoLISP ® , as<br />
ads_name values in ObjectARX and as like-named classes derived from<br />
ObjectARX. These values are always maintained in insert, xref, and wblock<br />
operations such that references between objects in a set being copied are<br />
updated to point to the copied objects, while references to other objects<br />
remain unchanged.<br />
Also, a group code range for “arbitrary” handles is defined to allow convenient<br />
storage of handle values that are not converted to entity names and<br />
then translated in insert, xref, or wblock.<br />
166 | Appendix B Advanced DXF Issues
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