Visualizing Quantitative Data
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Synonyms Real-world time; Intrinsic time; Logical time; Data time
Definition The valid time of a fact is the time when the fact is true in the modeled reality. Any subset of the time domain may be associated with a fact. Thus, valid timestamps may be sets of time instants and time intervals, with single instants and intervals being important special cases. Valid times are usually supplied by the user.
Key Points While other temporal aspects have been proposed, such as ‘‘decision time’’ and ‘‘event time,’’ closer analysis indicates that the decision and event time of a fact can be captured as either a valid time or a transaction time of some related fact. For example, consider a valid-time Faculty table with attributes Name and Position (that is, either Assistant Professor, Associate Professor, or Professor) that captures the positions of faculty members. The valid time then captures when a faculty member held a specific position. The ‘‘decision time’’ of a faculty member holding a specific position would be the time the decision was made to hire or promote the faculty member into that position. In fact, there are generally several decision times for a promotion: recommendation by departmental promotion and tenure committee, recommendation by department chair, recommendation by college promotion and tenure committee, recommendation by Dean, and finally decision by Provost. Each of these decisions may be modeled as a separate fact, with an (event) valid time that captures when that decision was made. #
2009 Springer ScienceþBusiness Media, LLC
Oracle explicitly supports valid time in its Workspace Manager. The support includes sequenced primary keys, sequenced uniqueness, sequenced referential integrity, and sequenced selection and projection. The term ‘‘valid time’’ is widely accepted; it is short and easily spelled and pronounced. Most importantly, it is intuitive. Concerning the alternatives, the term ‘‘real-world time’’ derives from the common identification of the modeled reality (opposed to the reality of the model) as the real world. This term is less frequently used. ‘‘Intrinsic time’’ is the opposite of extrinsic time. Choosing intrinsic time for valid time would require one to choose extrinsic time for transaction time. The terms are appropriate: The time when a fact is true is intrinsic to the fact; when it happened to be stored in a database is clearly an extrinsic property. However, ‘‘intrinsic’’ is rarely used. ‘‘Logical time’’ has been used for valid time in conjunction with ‘‘physical time’’ for transaction time. As the discussion of intrinsic time had to include extrinsic time, discussing logical time also requires the consideration of physical time. Both terms are used much less frequently than valid and transaction time, and they do not posses clear advantages over these. The term ‘‘data time’’ is probably the most rarely used alternative. While it is clearly brief and easily spelled and pronounced, it is not intuitively clear that the data time of a fact refers to the valid time as defined abo
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