Knowledge Management systems allow differing access levels to the same core body of knowledge and information.
These access levels are referred to as control perspectives and allow individuals to view information that is relevant to them and not be distracted by all the other knowledge within the systems.
The concept of Knoweledge Management can be thought of as a hierarchy. Within the ITIL v3 Service Strategy text book the hierarchy is referred to as DIKW - Data, Information, Knowledge, Wisdom.
This clever concept allows us to understand the increasing value of knowledge over time as it develops greater understanding and the ability to answer increasingly difficult questions (i.e. who, what, when, where, how, why).