External References. Basic concepts
Data sets in AutoCAD are a collection of all files that are needed to produce graphic output for an entire project or its subsets.
It may contain various file types: drawing files, image files, font files, shape files, plot style files and other types of linked files.
Drawing files (.DWG) of the same data set are usually linked to each other forming a hierarchical XREF structure.
To understand and be able to manipulate the dataset structure you need to know the properties of XREF links.
Attachment VS Overlay
AutoCAD uses two types of DWG references: attachments and overlays
All XREFs that are linked (attached or overlaid) directly to the parent file are visible in that file.
The second (and any subsequent) tier XREFs are only visible if they are attachments. In the schema below you will only see XREF1, XREF2, XREF3 and XREF5 from the PLOT file.
An easy way to remember: attachments are babies – they follow their parents. Overlays are teenagers – they never go with their parents.
Full Path, Relative Path and No Path.
XREFs and image files can be linked to master files using full path, relative path or no path.
Full path can be compared to a street address; it is an exact location of the XREF or attached image on your system. It includes server name or mapped drive name.
Relative path is like point-to-point directions from the parent file to its reference. It finds the reference based on the location the parent file. The relative path says: go several levels up the directory tree (usually to where the directory tree starts branching) then from that point go to the location indicated after the last “..”
In the following example the parent file is plot.dwg. The location of plot.dwg in the folder structure is shown on the picture on the left. All references (XREFs and images) are stored at ..EX4drawingsrefarch folder.
The relative path to REF1 and REF2 from the location of plot.dwg takes us two levels up to the EX4drawings folder, then from there to ..refarch.
This method makes the data sets portable because the path does not contain server name or mapped drive name.. In other words, if I copy the entire EX4drawings folder to any other location (CD, DVD or any network location), plot.dwg finds its references.
If no path is selected, AutoCAD will first look for XREFs and images in the same folder as the parent file, then in the search path folders. The support search paths, working search paths and project search paths are user profile specific and can be set up in Options->Files. The search path folders could vary for different systems and profiles.