tailieunhanh - Managing time in relational databases- P7

Tham khảo tài liệu 'managing time in relational databases- p7', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 5 THE CORE CONCEPTS OF ASSERTED VERSIONING 103 result is that asserted version bi-temporal tables have two pairs of dates representing two different time periods. They are the effective time period and the assertion time period of the rows in those tables. To assert a version is to claim that it is true. With any tables other than bi-temporal tables if something happens that makes a row no longer true that row is either updated or deleted. But with asserted version tables that isn t how we handle a row that we discover is not true. We handle it by assigning it an assertion end date or a transaction end date in the case of the standard temporal model representing the date on which we acknowledge that it is not true. Then we add another row to the table. This new row is a new assertion about the same version a new assertion about what the object is like during the same period of time. The multiple rows representing the same version are multiple assertions of that version. In a series of assertions about the same object during the same effective time period the later one in assertion time of every consecutive pair is a correction to the earlier one and the latest one of all is our current assertion about what is true. We may also note here that corrections and the versions they correct do not necessarily line up one to one. An error may span only part of a version or may span multiple versions or may span both. The ability to include in a table both corrections to versions as well as the original versions themselves is precisely what is lost when we remain with uni-temporal versions. This ability is precisely what we gain when we manage data bi-temporally. For example suppose that a row in a table states that policy P861 had a copay amount of 25 during the first six months of 2010. But on July 1st of that year we realized that the copay amount was actually 20 for that policy over that time period. If we were to overwrite that copay amount we would lose the .