Valid time

Abstract: An object-oriented framework for temporal data models.- An architecture for supporting interoperability among temporal databases.- Extended update functionality in temporal databases.- On transaction management in temporal databases.- Implementation options for time-series data.- Expressive power of temporal relational query languages and temporal completeness.- Transitioning temporal support in TSQL2 to SQL3.- Valid time and transaction time proposals: Language design aspects.- Point-based temporal extensions of SQL and their efficient implementation.- Applicability of temporal data models to query multilevel security databases: A case study.- An architecture and construction of a business event manager.- Discovering unexpected patterns in temporal data using temporal logic.- Querying the uncertain position of moving objects.- Temporal database bibliography update.- The consensus glossary of temporal database concepts - February 1998 version.- A glossary of time granularity concepts.

Abstract: INTRODUCTION Moving objects databases are particular cases of spatio-temporal databases that represent and manage changes related to the movement of objects. Unlike spatio-temporal applications associated with geographic phenomena where the identity of geographic features may change over time, in moving objects databases the objects maintain their identities but change their locations or shapes through time. That is, it is the geometric aspect of an object that changes rather than the object itself. Within this domain, the most suitable applications are those where objects are cars, airplanes, or any object with regular movements. Traditional DBMSs are not well equipped to handle data about moving objects. One of the reasons is that DBMSs assume that data is constant unless an explicit modification occurs, and this assumption is not adequate for handling continuously changing data such as the locations of moving objects. In traditional DBMSs, it is difficult to specify queries about spatial and temporal information. For example, a query such as " retrieve the cars that will intersect at a particular location in an hour " is not easily expressed with SQL. Finally, location of a moving object is inherently imprecise because the location stored in the database cannot always be the actual location of the object (Wolfson, 2002). Unlike traditional database applications, moving objects applications involve the following requirements, which are a subset of spatio-temporal applications requirements (Pfoser & Tryfona, 1998): • the need for representing objects, such as moving cars, with a position in space and an existence in time; • the need to capture the change of position over time. This change of position may be continuous or discrete; • the need for representing spatial relations among objects in time; and • the need to specify spatio-temporal integrity constraints .

Abstract: By supporting the valid and transaction time dimensions, bitemporal databases represent reality more accurately than conventional databases. The authors examine the issues involved in designing efficient access methods for bitemporal databases, and propose the partial-persistence and the double-tree methodologies. The partial-persistence methodology reduces bitemporal queries to partial persistence problems for which an efficient access method is then designed. The double-tree methodology "sees" each bitemporal data object as consisting of two intervals (a valid-time and a transaction-time interval) and divides objects into two categories according to whether the right endpoint of the transaction time interval is already known. A common characteristic of both methodologies is that they take into account the properties of each time dimension. Their performance is compared with a straightforward approach that "sees" the intervals associated with a bitemporal object as composing one rectangle, which is stored in a single multidimensional access method. Given that some limited additional space is available, the experimental results show that the partial-persistence methodology provides the best overall performance, especially for transaction timeslice queries. For those applications that require ready, off-the-shelf, access methods, the double-tree methodology is a good alternative.

Abstract: In applications like financial trading, scheduling, manufacturing and process control, time based predicates in queries and rules are very important. There is also a need to define lists of time points or intervals. The authors refer to these lists as calendars. The authors present a system of calendars that allow specification of natural-language time-based expressions, maintenance of valid time in databases, specification of temporal conditions in database queries and rules, and user-defined semantics for date manipulation. A simple list based language is proposed to define, manipulate and query calendars. The design of the parser and an algorithm for efficient evaluation of calendar expressions is also described. The paper also describes the implementation of time-based rules in POSTGRES using the proposed system of calendars. >