Declarative knowledge is defined as the factual information stored in memory and known to be static in nature. Other names, e.g. descriptive knowledge, propositional knowledge, etc. are also given. It is the part of knowledge which describes how things are. Things/events/processes, their attributes, and the relations between these things/events/processes and their attributes define the domain of declarative knowledge.
Procedural knowledge is the knowledge of how to perform, or how to operate. Names such as know-how are also given. It is said that one becomes more skilled in problem solving when he relies more on procedural knowledge than declarative knowledge.

References:
J.R.Anderson (1981) Cognitive Skills and Their Acquisition. Hillsdale, NJ, Lawrence Erlbaum.
G.J.Sussman (1973) A Computational Model of Skill Acquisition. Ph.D. thesis. Cambridge, MA, MIT.
D.B.Lenat (1983) Theory Formation by Heuristic Search. The nature of heuristics II: background and examples. Artificial Intelligence 21, pp.31-60.

Sample work:
Akın (1986), after referring to the two forms of knowledge as declarative and procedural, further categorizes them as specific and general. He places tokens and attributes under the declarative/specific and schemata and inference rules under the declarative/general categories. Transformations belong to the procedural/specific, while heuristics belongs to the procedural/general category of his taxonomy.

Ö.Akın (1986) Psychology of Architectural Design, London, Pion.

Uluoğlu’s (2000) survey results have shown that design knowledge is conveyed to the student in units (DE 2) which are built as a network of concepts normative or descriptive in nature. The lexicon employed in building the units, includes concepts (DE 1) that are names and attributes that are pertinent to the object and the subject. These are discussed under the declarative knowledge category. When it is procedural knowledge that is in use, the structure becomes directional and has a magnitudal impact on actions, affecting the course of design in differing degrees. Plan, search, control, representation, and transformation are introduced as procedural knowledge categories.

B.Uluoğlu (2000) Design knowledge Communicated in Studio Critiques. Design Studies, vol.21, issue 1, January, pp.33-58.

This article is written by Belkis Uluoglu for Designophy in 2006.