Within public relations research the book "Managing Public Relations" by Grunig and Hunt (1984) is perhaps the most cited piece of literature. In spite being more than 20 years old its takes on how to ensure high quality public relations work are still very relevant.
Grunig and Hunt (1984) highlights four models for how organizations can practice public relations:
1. The press agentry/publicity model
"...the press agents of the mid-19th century were the first full-time specialists to practice public relations. These press agents practiced the press agentry/ publicity model of public relations for such heroes as Andrew Jackson, Daniel Boone, Buffalo Bill Cody, and Calamity Jane. The most prominent of these practitioners was P.T. Barnum, who skilfully promoted his circus performers using the axiom, "There is a sucker born every minute."
2. The public information model
"At the beginning of the 20th century [...] a second model of public relations, the public information model, developed as a reaction to attacks on large corporations and government agencies by muckraking journalists. Leaders of these organizations realized they needed more than the propaganda of press agents to counter the attacks on them in the media. Instead, they hired their own journalists as public relations practitioners to write press "handouts" explaining their actions"
3. The two-way asymmetrical model
"Beginning with the Creel Committee during World War 1, however, some public relations practitioners began to base their work on the behavioral and social sciences. Foremost among these practioners was Edward L. Bernays. [...] ... the introduction of a scientific approach made the practice two-way: Practitioners both sought information from and gave information to publics. Sciences also are based on theories; and the theories introduced by Bernays were those of propaganda, persuasion, and the "engineering of consent.""
4. The two-way symmetrical model
"J. Grunig and Hunt (1984) identified many of the assumptions of the fourth model of public relations, the tw-way symmetrical model, in the writings of practitioners such as Lee, Bernays, and John Hill. These assumptions included "telling the truth", "interpreting the client and public to one another," and "management understand the viewpoints of employees and neighbors as well as employees and neighbours understanding the viewpoints of management." [...] The two-way symmetrical model makes use of research and other forms of two-way communication. Unlike, the two-way asymmetrical model, however, it uses research to facilitate understanding and communication rather than to identify messages most likely to motivate or persuade publics"
The theory of the four models is normative. For the clever reader it should not be that hard to guess which one is the model public relations practitioners should strive for? :-)
Citations are from Grunig & Grunig (1992).