© 2001 IEEE. An unambiguous definition of space is necessary before any attempt made to develop product or process models for concurrent engineering in the AEC Industry. The ambiguity is the result of different and even conflicting approach to its definition in the various phases of the building life cycle for different stakeholders, e.g. Architects, Engineers, and Building Services Engineer etc. Some researchers consider space as an abstract property of things, while others consider as a thing itself. Regardless of the definition, the space can be referred to as a collector of material objects and also as an object itself. This paper investigates the existing concepts & criteria of definition in various phases, compares with the factual and ontological meaning, and specifies conceptual schemas for representation of space, geometry, and buildings.