J. Clifford and A. Rao. A Simple, General Structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in Information Systems, pages 17--30. North-Holland, 1988.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....of the Sunday is (1998, 7, 2) 6. Related Work Much work has been done on the problem of granularity representation in temporal database area as well as other areas like arti cial intelligence and real time systems. Some of them address the formalization of time granularity systems [BWJ98,CR87,Dea89,MMCR92] Our work is an instantiation of the general framework proposed in [BWJ98] A symbolic representation of granularities that allows natural language expression was proposed in [LMF86] on the basis of structured collections of inter Ning, Wang and Jajodia An Algebraic ....

J. Cliord and A. Rao. A simple, general structure for temporal domains. In Proc. of the Conference on Temporal Aspects in Information Systems, pages 23-30, 1987.

....where it is located on the time axis; it can stand for any block of 31 consecutive days. Anchored and unanchored temporal information is usually available in multiple granularities. Such information is prevalent in various fields: clinical data [3] realtime systems [2] office information systems [4, 11]. Clearly, many applications require support for (a) unanchored temporal primitives that are specified in different (for example, 3 months, 150 seconds) and mixed granularities (for example, 2 hours and 20 minutes) and (b) anchored temporal primitives that are specified in different ....

J. Clifford and A. Rao. A Simple, General Structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in Information Systems, pages 17--30. North-Holland, 1988.

....leads to the following definitions: Definition 4.1 1. is the set of event specifications. 2. is the time axis for event recordings, with a total order . 3. is time axis for event occurences, also with a total order . Both the and time axis can be defined in a multitude of ways, see e.g. [CR87], WJL91] or [All84] 4. is the set of all event occurences. An event occurence is identified by an event specification and the point of time at which the event occurs. 5. is the set of all event recordings. A recording of an event occurence is identified by the recorded event occurence, and the ....

J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

....for the minimal network problem are proposed. 1 Introduction Human activities heavily relate to calendar units and clock units (e.g. weeks, months, hours and seconds) System support and reasoning involving these units, also called granularities, has been recognized to be an important issue [Hob85, CR87, TSQL2]. However, many different definitions of granularities exist in the literature and, moreover, these definitions are often quite restrictive. The A preliminary version of this paper appeared in the Proceedings of 3rd International Workshop on Temporal Representation and Reasoning, Key West, FL, ....

.... a polynomial algorithm existed, consistency checking would be polynomial since the tightest constraint between each pair of variables in an inconsistent constraint network is ffalseg (i.e. not satisfiable) 5 Related work A first formalization of a time granularity system is probably that of [CR87]. However, the system proposed in [CR87] as well as most of the time granularity systems proposed in the literature (e.g. Dea89, MMCR92] is quite restrictive. For example, these systems often impose a total order on granularities. The restrictions are usually motivated by useful formal and ....

[Article contains additional citation context not shown here]

J. Clifford and A. Rao, A simple, general structure for temporal domains in Proc. of the Conference on Temporal Aspects in Information Systems, France, 1987, pp. 23--30.

....systems Geographic information is usually speci ed according to a varying time scale [14] For example, vegetation uctuates according to a seasonal cycle, while temperature varies daily. oce information systems temporal information is available in di erent time units of the Gregorian calendar [2, 8, 21]. For example, employee wages are usually recorded in the time unit of hours while the history of sales are categorized according to months. Clearly many applications require support for both anchored and unanchored temporal primitives that are speci ed in di erent and mixed granularity. Without ....

J. Cliord and A. Rao. A Simple, General Structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, (Eds.), Temporal Aspects in Information Systems, NorthHolland, Amsterdam, 17-30, 1988.

....and discrete domains of time. This allows a temporal model to provide support not only for applications which usually need a discrete temporal domain, but also for applications that need dense time as an abstraction. This is in contrast to recent proposals that handle multiple granularities [4, 13, 5, 18, 2, 17, 15]. These proposals assume a single underlying temporal domain which is usually discrete. The contributions of this paper can be summarized as follows: 1) We present a simple, general framework for supporting temporal primitives which allows seamless integration of dense and discrete domains of ....

J. Clifford and A. Rao. A Simple, General Structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in Information Systems, pages 17--30. North-Holland, 1988.

....is usually specified according to a varying time scale [Flo91] For example, vegetation fluctuates according to a seasonal cycle, while temperature varies daily. office information systems Gamma temporal information is available in different time units of the Gregorian calendar [BP85,CR88,MPB92] For example, employee wages are usually recorded in the time unit of hours while the history of sales are categorized according to months. Design Space. A calendar is composed of an origin, a set of calendric granularities, and a set of conversion functions. The origin marks the start of ....

J. Clifford and A. Rao. A Simple, General Structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in Information Systems, pages 17--30. North-Holland, 1988.

....advantage of the multitude of temporal types. On the other hand, the dependence on the temporal types limits the ability to express certain intuitive aggregates that are expressible in TSQL2. Another research area that is related to the current paper is the work on multiple calendars, e.g. CR87, NS92, CSS94, SS92] These work are more focused on the management or description of calendars but not on incorporating them into query languages. 4 3 Data model This section introduces a data model that is an extension of the one presented in [WJS95] 3.1 Temporal types We start with ....

J. Clifford and A. Rao. A simple, general structure for temporal domains. In Proceedings of the Conference on Temporal Aspects in Information Systems, pages 23--30, France, May 1987.

....issues in one way or another. We note from Table 1 that not much work has been carried out in the temporal database research community towards comprehensively modeling the basic temporal entities. The few works that 2 Citation Calendar(s) Granularities Time primitives Granularity conversions [CR87] No support Multiple Anchored Anchored [WJL91] WJS93] No support Multiple Anchored Anchored [BP85] MPB92] No support Multiple Anchored Anchored [MMCR92] No support Multiple Anchored Anchored [Sno95b] Multiple Multiple Anchored Unanchored Anchored Table 1: Temporal models supporting ....

....not clear how these translations are carried out though. Most of the research on temporal relational models has concentrated on modeling temporal information with a single underlying granularity. There have been some recent proposals however, that handle multiple granularities. Clifford and Rao [CR87] introduce a general structure for time domains called a temporal universe. A temporal universe consists of a totally ordered set of granularities. Operations are defined on a temporal universe, which basically convert different anchored times to a (common) finer granularity before carrying out ....

J. Clifford and A. Rao. A Simple, General Structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in Information Systems, pages 17--30. North-Holland, 1987.

....in this text, we show how this general process can be distinguished for the analysis and generation perspectives. 3 The structure of the TRC We could be tempted, considering the examples of the previous section, to represent the TRC as a linear order with the inclusion relation, as suggested in [5] and [8] This will not work. Consider for example the TLA le printemps 1994 (spring 1994) The inclusion relation, in this case, cannot be represented explicitly in the TRC, since a year cannot be decomposed into seasons. Winter is a season that overlaps two years. Consequently, the inclusion ....

J. Clifford and A. Rao. A simple, general structure for temporal domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal aspects in information systems, pages 17--28. North-Holland, Amsterdam, 1991.

....is interesting, as it allows the application of well established results (Theorem 13, for example) Granularity We view time as isomorphic to the naturals. The set of natural numbers f1; 2; 3; g is denoted N. Our starting point is a classical, set theoretic approach to time granularity (Clifford Rao 1987), where a given granularity constitutes a partition of the set of granules of a finer granularity. But unlike other approaches, we take as definition for granularity not the partition itself, but the corresponding equivalence relation that can be constructed from it (Wijsen 1998; 1999) More ....

Clifford, J., and Rao, A. 1987. A simple, general structure for temporal domains. In Rolland, C.; Bodart, F.; and Leonard, M., eds., Temporal Aspects in Information Systems. Amsterdam, The Netherlands: North-Holland/IFIP. 17--28.

....into the theory through the algebraic structure , where is a (discrete, totally ordered) time axis, and a set of functions over . For the moment, is assumed to contain the one step increment operator , and the comparison operator . Several ways of defining a time axis exist, see e.g. CR87] WJL91] or [All84] The time axis is the axis along which the application model evolves. With this time axis, an application model history is a (partial) mapping . is the set of all such histories. In a later section, we will pose well formedness restrictions on histories. Other time models ....

J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

....incorporated into the theory through the algebraic structure , where is a (discrete, totally ordered) time axis, and a set of functions over . For the moment, is assumed to contain the one step increment operator , and the comparison operator . Several ways of defining a time axis exist, see e.g. [12], 54] or [2] Other time models are possible, for example, in distributed systems a relative time model might be used. For a general survey on time models, see [44] The linear time model is usually chosen in historical databases (see for example [49] 2. The set is the domain for the ....

J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

....is called an instant ; the time between two instants is known as a time period (period for short) and a length, or unanchored segment, of the time line is an interval . The timeline segment is partitioned into a finite number of smaller segments each of which is called a chronon [Ariav 1986; Clifford and Rao 1987; Jensen et al. 1994] A chronon is the smallest amount of time that can be represented in the implementation. The chronons are consecutively labeled with the integers in the sequence 0; N , where N is the number of values that a timestamp can represent. 3.2 Indeterminate Instants An ....

Clifford, J. and Rao, A. 1987. A Simple, General Structure for Temporal Domains. In Proceedings of the Conference on Temporal Aspects in Information Systems (France, May 1987), pp. 23--30. AFCET.

....databases can fully support this mixing. This paper o ers a practical design for that support. We see the following as the seven main contributions of this paper. First, various semantics have been proposed for temporal operations that have operands at different granularities [Adiba et al. 1985, Cli ord Rao 1987, Lorentzos 1992, Melton Simon 1993, Montanari et al. 1992, Sarda 1993, Wang et al. 1995, Wiederhold et al. 1991] For instance, in a comparison operation between a time known to the granularity of days and one known to the granularity of hours, the comparison could be performed at days, or it ....

....f1997 01 01 days ; 1997 01 02 days ; 1997 12 31 days g. 3. 4 Instants An event occurs at a particular time point in T [Jensen Dyreson 1998] In general, the database cannot know this precise time, both because the measurement of the time is imprecise at the resolution of the time domain [Cli ord Rao 1987], and because the database cannot always accurately represent an arbitrary element of the time domain (e.g. when T is continuous) For example, assume that a wristwatch reports that the current time is 3:45:23 P.M. This means that it is (was) sometime during that second, but it is unknown ....

[Article contains additional citation context not shown here]

Cliord, J. and A. Rao. \A Simple, General Structure for Temporal Domains, " in Proceedings of the Conference on Temporal Aspects in Information Systems. AFCET. France: May 1987, pp. 23-30.

....scheme consists of 4 relation schemes: 1 TS DOMAIN is defined as an appropriate domain for time stamps, e.g TS DOMAIN = MONTH DAY YEAR HOUR MINUTE SECOND. SECOND = MINUTE = 0, 59 , HOUR = 0, 23 , A relation TS DOMAIN TS DOMAIN orders time stamps in the usual way [22, 23]. We use as an abbreviation for or = 2 D DOMAIN is defined as an appropriate domain for temporal distances, e.g D DOMAIN = NO OF DAYS = 0days, 1day, 2days, A relation D DOMAIN D DOMAIN orders temporal distances (durations) in the usual way [22. 23] We use = as abbreviation for ....

J. Clifford, A. Rao. A simple, general structure for temporal domains. In C. Rolland, M. Leonard, F. Bodard (Eds.), Proc. TAIS Conference, Temporal Aspects in Information Systems, pp. 23-28, Sophia Antipolis, France, 1987.

....will commonly have operands at different granularities. For instance, a comparison operation might compare a time known to the granularity of a day to a time known to the granularity of an hour. Various semantics have been proposed for temporal operations on mixed granularities [ABQPdO85, CR87, MS93, MMCR92, Sar93, WJS93, WJL91] In this paper we propose two simple operations that can be utilized to support all of the previous semantics for temporal operations. Second, some useful granularities are nonmetric or irregular measurement schemes. For example, in the Gregorian calendar, ....

....by an instant timestamp is never precisely known. At best, only the granule during which it is located is known. The distinction between chronons and instants captures the reality of temporal measurements in that all such measurements are imprecise with respect to instants in the time line [CR87] For example, if our wristwatch says that the current instant (i.e. the time now ) is 3:45:23 P.M. it means that it is sometime during that second, not the entire second. We simply cannot measure individual instants; instants are too small. In this sense, our model of time is faithful to ....

[Article contains additional citation context not shown here]

J. Clifford and A. Rao. A Simple, General Structure for Temporal Domains. In Proceedings of the Conference on Temporal Aspects in Information Systems, pages 23--30, France, May 1987. AFCET.

....intelligence formalisms temporal database models adopt very similar notions of time. Most researchers seem to agree that a linearly ordered discrete temporal universe is enough for their applications. 19 The elements of the discrete universe are points or line segments called chronons [CR88] Whenever intervals are needed they are usually defined by pairs of points or chronons. ffl Is the integration of time into the static model tight or loose Some temporal models are consistent extensions of static models i.e. every construct or operation of the static model has a ....

J. Clifford and A. Rao. A Simple, General Structure For Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in Information Systems, pages 17--28. North-Holland, 1988.

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J. Clifford and A. Rao. A Simple, General Structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in Information Systems, pages 17--30. North-Holland, 1988.

No context found.

J. Cli#ord and A. Rao. A Simple, General Structure for Temporal Domains. In Proceedings of the Conference on Temporal Aspects in Information Systems, pages 23--30, France, May 1987. AFCET.

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J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

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J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

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J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

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J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

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J. Clifford and A. Rao. A simple, general structure for Temporal Domains. In C. Rolland, F. Bodart, and M. Leonard, editors, Temporal Aspects in information Systems, pages 17--28. North-Holland/IFIP, Amsterdam, The Netherlands, 1987.

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