Errors can be due to instrumental or conceptual problems in measuring the data. Decision Support Systems help to manage the uncertainty of data , they take the data and turn it into a decision. Knowledge is a guide to informed practice. The process which the system takes the user through should lead to greater understanding and the formation of plans. It helps the user make concrete sense out of the abstract.
Most computer based systems separate the knowledge base from the inference engine.
The inference engine is the part of the a decision support system which 'infers' a conclusion based on the data available. The user interacts with the knowledge contained in the database through the application system user interface. Lack of accurate data recording in the past or the cost of recording it now will lead to uncertainty developing in the system. The information can be plain wrong, or an exceptions to the rule used may exist. The knowledge base may be shallow, or the sheer size of the domain of knowledge is so great that there are opportunities for unexplained events to occur.