Another must-read for any serious OO practitioner. Object-Oriented Modeling and Design Rumbaugh, James et. A must-read, even if you are looking at the Unified Model documents. A Manager's Guide Taylor, David. The single, best introduction to OO thinking on the market.
New focus is on business objects and components.
Still the single, best introduction to OO thinking on the market. Object Technology Revolution, The Guttman, Michael, Jason R. Matthews. John Wiley 1995 Focus is on why objects should be important to you from a business perspective, rather than just a technical view. Unique in its approach and every bit as accessible as David Taylor's books. Very broad in its coverage without getting bogged down in the minutiae of the notation.