Each component of the model that is subject to change will be evaluated to assess the way in which past (historical) values should be treated. When we refer to a component we mean:
Entity: a set of circumstances or a dimension (e.g., customer details or product dimension)
Relationship: for example, a hierarchy
Attribute: for example, the customer's address
Each component will then be given a classification. This is called the retrospection[1] of the component. Retrospection has three possible values:
Retrospection means literally “looking back into the past.”
True
False
Permanent
True retrospection means that the object will reflect the past faithfully. It enables queries to return temporal subsets of the data reflecting the partitioning of historical values. Each dimension, relationship, and attribute value will, in effect, have a lifespan that describes the existence of the object. An object may have a discontinuous lifespan, that is, many periods of activity, punctuated by periods of inactivity. True retrospection is the most accurate portrayal of the life of a data warehouse object.
False retrospection means that the view of history will be altered when the object's value changes. In simple terms, when changes occur, the old values will be overwritten and are, therefore, lost. It is as though the old values had never existed.
Permanent retrospection means that the value of the object will not change over time.
Each component of the model that is subject to change will be evaluated to assess the way in which past (historical) values should be treated. When we refer to a component we mean:
Entity: a set of circumstances or a dimension (e.g., customer details or product dimension)
Relationship: for example, a hierarchy
Attribute: for example, the customer's address
Each component will then be given a classification. This is called the retrospection[1] of the component. Retrospection has three possible values:
Retrospection means literally “looking back into the past.”
True
False
Permanent
True retrospection means that the object will reflect the past faithfully. It enables queries to return temporal subsets of the data reflecting the partitioning of historical values. Each dimension, relationship, and attribute value will, in effect, have a lifespan that describes the existence of the object. An object may have a discontinuous lifespan, that is, many periods of activity, punctuated by periods of inactivity. True retrospection is the most accurate portrayal of the life of a data warehouse object.
False retrospection means that the view of history will be altered when the object's value changes. In simple terms, when changes occur, the old values will be overwritten and are, therefore, lost. It is as though the old values had never existed.
Permanent retrospection means that the value of the object will not change over time.