The Experts below are selected from a list of 9837 Experts worldwide ranked by ideXlab platform
Randall Weis - One of the best experts on this subject based on the ideXlab platform.
-
Allen Relationship and Other Queries
Managing Time in Relational Databases, 2010Co-Authors: Tom Johnston, Randall WeisAbstract:This chapter discusses how to query asserted version tables. Many queries, especially the ad hoc queries written by nontechnical database users, will be directed against nontemporal or unitemporal views of asserted version tables, not against those bitemporal tables themselves. But many queries will be written directly against those physical tables, especially production queries. In that case, the effective time period specified on the query, and which qualifies the result set, will have to be compared to the effective time periods of the rows targeted by the query; and as we know from our review of the Allen Relationships, there are 13 different ways in which those two time periods may be positioned with respect to one another. This chapter examines thirteen Allen Relationships, and each nonleaf node in the taxonomy of Allen Relationships. It describes the Allen Relationships as they hold between two time periods, between a time period and a point in time, and also between two points in time. These Relationships are expressed in terms of time periods represented with the closed-open convention, and provide a sample query for each one. Many of the Allen Relationships are used by the Asserted Versioning to enforce temporal entity integrity (TEI) and temporal referential integrity (TRI).
Tom Johnston - One of the best experts on this subject based on the ideXlab platform.
-
Allen Relationship and Other Queries
Managing Time in Relational Databases, 2010Co-Authors: Tom Johnston, Randall WeisAbstract:This chapter discusses how to query asserted version tables. Many queries, especially the ad hoc queries written by nontechnical database users, will be directed against nontemporal or unitemporal views of asserted version tables, not against those bitemporal tables themselves. But many queries will be written directly against those physical tables, especially production queries. In that case, the effective time period specified on the query, and which qualifies the result set, will have to be compared to the effective time periods of the rows targeted by the query; and as we know from our review of the Allen Relationships, there are 13 different ways in which those two time periods may be positioned with respect to one another. This chapter examines thirteen Allen Relationships, and each nonleaf node in the taxonomy of Allen Relationships. It describes the Allen Relationships as they hold between two time periods, between a time period and a point in time, and also between two points in time. These Relationships are expressed in terms of time periods represented with the closed-open convention, and provide a sample query for each one. Many of the Allen Relationships are used by the Asserted Versioning to enforce temporal entity integrity (TEI) and temporal referential integrity (TRI).