What PMBOK is not!
The PMBOK Guide was created by the Project Management Institute (PMI) with two specific objectives:
• To identify and describe that subset of the current project management body of knowledge that is generally accepted.
• To provide a common lexicon within the profession and practice for talking and writing about project management.
The expression "generally accepted" means that the knowledge and practices described are applicable to most projects most of the time, and that there is a widespread consensus about their value and usefulness. Generally accepted does not mean that the knowledge and practices described are or should be applied uniformly on all projects; the project management team is always responsible for determining what is appropriate for any given project.”
The PMBOK Guide provides a rather extensive list of practices and further identifies numerous tools and techniques applicable to most projects. It does not impose any prescriptive detail. It is the responsibility of the project management team to select the appropriate practices applicable to their specific application area.
A methodology is much more prescriptive. It identifies specific processes and techniques to be employed in the solution of a problem or the creation of a product or service. A methodology is very specific to an application area and cannot be applied uniformly to other application areas. A methodology applied in building construction will not be acceptable for software development.
As such, the PMBOK Guide is not and does not suggest a methodology. The PMBOK Guide is more a PM practice reference handbook.
More information on methodologies will be found under Methodologies > Project Life Cycles as well as under Methodologies > Development Models.