Adobe Illustrator Artwork (AI) is a proprietary file format developed by Adobe Systems for representing single-page vector-based drawings in either the EPS or PDF formats. The .ai filename extension is used by Adobe Illustrator.

Early versions of the AI file format are true EPS files with a restricted, compact syntax, with additional semantics represented by Illustrator-specific DSC comments that conform to DSC's Open Structuring Conventions. These files are identical to their corresponding Illustrator EPS counterparts, but with the EPS procsets (procedure sets) omitted from the file and instead externally referenced using %%Include directives.

Recent versions of the AI file format, including the PDF-based formats and recent EPS formats, are based on a native format called PGF that is unrelated to both EPS and PDF. PDF compatibility is achieved not by extending the PDF format, but by embedding a complete copy of the native PGF data within the PDF file. The same kind of ?dual path? approach is also used when recent versions of Illustrator are saving EPS-compatible files.

Adobe Illustrator is not the only program that can edit .ai files. Both Inkscape (a GPL licensed program) and CorelDRAW (another Proprietary program) can natively edit this file format.

References

• Adobe Illustrator File Format Specification?the official specification for the original EPS-based formats

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