J. Cli#ord and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In S. Navathe, editor, In Proceeding of ACM SIGMOD, pages 247--265, Austin, TX, May 1985.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....to specify when inapplicable nulls could occur, we adapted the concept of lifespans, whose importance had previously been recognized in the context of data models. The HRDM model associates explicit lifespans with each attribute of a relation schema and with each tuple of a relation instance [CT85, CC87, CC93] The HRDM goes further than other data models in incorporating lifespans, but it still does not explicitly record the lifespans of attributes of individual tuples surrogates (HRDM tuples correspond to our object representing surrogates) as we do. Rather, the lifespan of an attribute ....

.... because there exists a temporal dependency between Dept and Salary (in fact, many tuples represent the value of one attribute changing while the value of the other remained as before) ut 29 The type of redundancy identified by TNF has been mentioned in the past by several researchers (e.g. CT85, GV85, Gad88, GY91] Most often, it has been used for motivating a non first normal form data modeling approach where time is associated with attribute values rather than with tuples, because that approach avoids the redundancy. The problem with such data models, as discussed in Section 2.3, is ....

J. Clifford and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In S. Navathe, editor, ACM SIGMOD International Conference on the Management of Data, pages 247--265, Austin, TX, May 1985.

....taxonomy. Table 1 summarizes how previous work is represented in the taxonomy. For each operator defined in previous work, the table lists the defining publication, researchers, the corresponding taxonomy operator, and any restrictions assumed by the original operators. In early work, Clifford [CT85] indicated that a an Table 1: Temporal Join Operators Operator Initial Citation Taxonomy Operator Restrictions JOIN [CC87] Theta join None EQUIJOIN [CC87] Equijoin None NATURAL JOIN [CC87] Natural Join None TIME JOIN [CC87] Cartesian Product 1 T join [GS91] Cartesian Product None ....

J. Clifford and A. Uz Tansel. On An Algebra For Historical Relational Databases: Two Views. In Proceedings of the ACM SIGMOD International Conference on Management of Data, pages 1--8, 1985.

....management is motivated by the need to support decision making based not only on current data but also on historical information. Efforts on temporal models, temporal languages, storage structures, and access methods for the implementation of temporal database systems have been reported in [AND82, CLI83, KLO83, SCH83, LUM84, CLI85, SNO85, ADI86, ARI86, GAD86, TAN86, SEG87, SNO87, LOR88, NAV89, TAN89, ELM90a, ELM90b, ROS91, SU91]. However, these research on temporal DBMS concentrate only on the management of the explicitly stored temporal data [MAI91] techniques for managing the data which are not explicitly stored but can be derived from the temporal dependencies relationships of the existing data are not provided. ....

Clifford, J., and Tansel, A.U., "On an Algebra for Historical Relational Databases: Two Views," Proc. of the ACM SIGMOD Int'l Conf., 1985, pp. 247-265.

.... of databases with NOW and the querying of such databases has been covered extensively elsewhere [10] However, the impact on modifications of the presence of NOW in the database as well as in the modification statements themselves has not been covered, even though many temporal data models, e.g. [3, 6, 7, 8, 17, 20, 26, 32], assume that NOW can be stored in the database. Before defining the semantics of modifications on variable databases, we specify three requirements to the accommodation of NOW . Requirement R1 The conventional insert, delete, and update statements should be extended to permit constant ....

J. Clifford and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In Proceedings of the ACM SIGMOD Conference, pp. 247--265, 1985.

....desired. It is also possible to delete a version of an object when that particular version is no longer of interest. The reason for providing this rather primitive level of version support is that different EXODUS applications may have widely different notions of how versions should be supported [Ston81, Dada84, Clif85, Klah85, Snod85, Katz86]. We do not omit version management altogether for efficiency reasons it would be prohibitively expensive, both in terms of storage space and I O cost, to maintain versions of large objects by maintaining entire copies of objects. Versions of large objects are maintained by copying and ....

Clifford, J., and A. Tansel, "On An Algebra for Historical Relational Databases: Two Views," Proc. of the 1985 SIGMOD Conf., Austin, Texas, May 1985.

....the current version, and all of the preceding versions are simply marked (in their object headers) as being old versions. The reason for only providing a primitive level of version support is that different EXODUS applications may have widely different notions of how versions should be supported [Ston81, Dada84, Katz84, Bato85, Clif85, Klah85, Snod85, Katz86]. We do not omit version management altogether for efficiency reasons it would be prohibitively expensive, both in terms of storage space and I O cost, to maintain versions of large objects by maintaining entire copies of objects. Versions of large storage objects are maintained by copying ....

Clifford, J., and A. Tansel, "On An Algebra for Historical Relational Databases: Two Views", Proceedings of the 1985 SIGMOD Conference, Austin, Texas, May 1985.

.... of version support is that different EXODUS applications may have widely different notions of how versions should be supported, as evidenced by the wide range of version related proposals in the recent literature [Stonebraker 1981, Dadam, et al. 1984, Katz and Lehman 1984, Batory and Kim 1985, Clifford and Tansel 1985, Klahold, et al. 1985, Snodgrass and Ahn 1985, Katz, et al. 1986] Therefore, we leave the maintenance of data structures such as graphs of the versions and alternatives of objects to a higher level of the system, a level that will vary from application to application (unlike the storage system) ....

Clifford, J., and A. Tansel, "On An Algebra for Historical Relational Databases: Two Views", Proceedings of the 1985 SIGMOD Conference, Austin, Texas, May 1985.

....to specify when inapplicable nulls could occur, we adapted the concept of lifespans, whose importance had previously been recognized in the context of data models. The HRDM model associates explicit lifespans with each attribute of a relation schema and with each tuple of a relation instance [CT85, CC87, CC93] The HRDM goes further than other data models in incorporating lifespans, but it still does not explicitly record the lifespans of attributes of individual tuples surrogates (HRDM tuples correspond to our object representing surrogates) as we do. Rather, the lifespan of an attribute ....

.... in TNF, because there exists a temporal dependency between Dept and Salary (in fact, many tuples represent the value of one attribute changing while the value of the other remained as before) ut The type of redundancy identified by TNF has been mentioned in the past by several researchers (e.g. CT85, GV85, Gad88, GY91] Most often, it has been used for motivating a non first normal form data modeling approach where time is associated with attribute values rather than with tuples, because that approach avoids the redundancy. The problem with such data models, as discussed in Section 2.3, is ....

J. Clifford and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In S. Navathe, editor, ACM SIGMOD International Conference on the Management of Data, pages 247--265, Austin, TX, May 1985.

....and for measurement of a magnetic field taking at regular intervals, continuous behavior would be assumed. A time sequence collection (TSC) is then a set of time sequences. Clifford 2 The Historical Relational Data Model [35] a refinement of the model associated with a valid time algebra [36], is unique in that it associates timestamps with both individual tuples and with individual attribute values of the tuples. The data model allows two types of objects: a set of chronons, termed a lifespan,anda valid time relation, where each attribute in the relation schema and each tuple in the ....

....Note also that we have chosen the most straightforward representation for an attribute whose value is a function. Because attribute values in both Clifford s model and Gadia s models, which we describe later, are functions, they have many physical representations. 2 Tan s e l Tansel s model [36, 37] was designed to support the calculus based query language HQuel [38] and, later, the Time by Example language [52] The model allows only one type of object: the valid time relation. However, four types of attributes are supported: Attributes may be either non time varying or time varying, and ....

Clifford, J. and A. U. Tansel. "On an Algebra for Historical Relational Databases: Two Views," in Proceedings of ACM SIGMOD International Conference on Management of Data. Ed. S. Navathe. Association for Computing Machinery. Austin, TX: May 1985, pp. 247--265.

....AssistantMgr 922 DATABASE DESIGN after having reached a certain capacity. This means that AssistantMgr is not lifespan equal to the other attributes, e.g. Manager and Capacity. 2 The importance of lifespans in temporal databases has been recognized in the context of data models in the past (cf. [6, 5, 11]) Our use of lifespans for database design differs from the use of lifespans in database instances. In particular, using lifespans during database design does not imply any need for storing lifespans in the database. 3.5 Time Patterns of Individual Time Varying Attributes In order to capture ....

J. Clifford and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In S. Navathe, editor, ACM SIGMOD International Conference on the Management of Data, pp. 247--265 (1985).

....updated or deleted, previous versions of records are overwritten and lost from the database. In many applications, however, it is necessary to retain and maintain access to the old versions of these records, so that queries about the past states of the database can be answered. A temporal database [3, 23, 22, 20] provides automatic storage and management of old (versioned) data. For example, consider a departmental store database tracking the transactions associated with different items sold by its various departments. Figure 1(a) shows a hypothetical snapshot relation in this database; only the most ....

J. Clifford and A. Tansel. On an algebra for historical relational databases: Two views. In Proc. of the ACM SIGMOD Conference, 1985.

....of a certain account in a particular month and account holders are stored in terms of days, she naturally assumes that the answer is someone who is the account holder of that account on all the days within that month. Researchers have long realized such richness of semantics in temporal data [CT85, SS87, Tan87] and provided various operators in different query languages for the users to code the semantic assumptions into queries [SS87, Tan87] For the aforementioned balance query, the user would use a last (or similar) operator in her query to retrieve the appropriate balance. We argue, ....

....database with the assumptions built in, instead of having to code them into queries. Thus, in this study, the query language for the user is a simple extension of the relational calculus (the extension is for incorporating the temporal dimension, not for semantic assumptions) Other researchers [CT85, WJL91, CI94] also recognized the importance of semantic assumptions in temporal databases. Clifford [CT85] pointed out the use of interpolation in temporal databases; however, the query evaluation was not formalized. Clifford and Isakowitz [CI94] dealt with formalizing the semantics of variables ....

[Article contains additional citation context not shown here]

J. Clifford and A.U. Tansel. On an algebra for historical relational databases: Two views. In S. Navathe, editor, Proc. ACM SIGMOD Int. Conf. on Management of Data, pages 247--265, Austin, TX, May 1985. ACM. 26

....a summary of the status of research on temporal databases and Kline [13] provides a recent bibliography. The prevailing approach to modelling the time dimension in databases is, in one form or another, the use of an explicit representation of time at both the tuple level and the attribute level [3, 4, 7, 9, 20]. Most of the temporal algebras reported in the literature are not algebras in the mathematical sense, i.e. they are not closed since expressions do not always evaluate to time varying relations of the underlying models. This is one of the consequences of the use of an explicit time dimension in ....

....of time varying data and to manipulate complex time varying attributes and temporal elements. Some algebras are not unisorted; in other words, the results of expressions can be timevarying relations, snapshot relations, or even temporal elements such as intervals. For example, Clifford s [3] and Sarda s [20] algebras include an operator to drop the time components of a given time varying relation to obtain snapshot relations, and Gadia s [9] algebra allows temporal elements. Very few algebras [16, 26] support the standard definitions of algebraic operators such as intersection and ....

[Article contains additional citation context not shown here]

J. Clifford and A. U. Tansel. On an algebra for historical relational databases: Two views. In S. Navathe, editor, Proceedings of the 1985 ACM SIGMOD International Conference on Management of Data, pages 247--265. ACM Press, 1985.

.... database community, two basic time models have been proposed: the continuous model, in which time is viewed as being isomorphic to the real numbers, with each real number corresponding to a point in time, and the discrete model , in which time is viewed as being isomorphic to the integers [Clifford Tansel 1985]. In the discrete model, the continuous time line is partitioned into line segments. Each segment is called a chronon [Ariav 1986, Clifford Rao 1987] A chronon is the smallest duration of time that can be represented. We choose to use the discrete model. We do not assume a specific granularity ....

Clifford, J. and A.U. Tansel. "On an Algebra for Historical Relational Databases: Two Views," in Proceedings of ACM SIGMOD International Conference on Management of Data. Ed. S. Navathe. Association for Computing Machinery. Austin, TX: May 1985, pp. 247--265.

.... community, two basic time models have been proposed: the continuous model , in which time is viewed as being isomorphic to the real numbers, with each real number corresponding to a point in time, and the discrete model , in which time is viewed as being isomorphic to the natural numbers [Clifford Tansel 1985]. We choose to use a discrete model. We propose that time is modeled by a closed interval on the real number line. Since it is a closed interval, time has both an origin and an endpoint. The time line can be subdivided into a finite number of contiguous, pairwise disjoint subintervals. Each ....

Clifford, J. and A.U. Tansel. "On an Algebra for Historical Relational Databases: Two Views," in Proceedings of ACM SIGMOD International Conference on Management of Data. Ed. S. Navathe. Association for Computing Machinery. Austin, TX: May 1985, pp. 247--265.

....per year. 2. 3 Model of the Time Line In temporal databases research three time models have been proposed: The Continuous model where time is isomorphic to the real numbers, the Dense model where time is isomorphic to the rationales and the Discrete Model where time is isomorphic to the integers [CLIFFORD85]. The TAU Model adopts the Discrete Model of time because of its better representation and manipulation on databases. Time axis can be partitioned into a finite number of discrete segments which are called granules [WIEDERHOLD91A] The choice of a partitioning scheme is termed as granularity. A ....

J. Clifford and A. U. Tansel, "On an Algebra for Historical Relational Databases: Two Views", sigmod, Navathe, S. (Ed.), acm, Austin, TX, 1985, pp. 247-265. The TAU Time Model Page 23

....all EmpS surrogates, attributes EName and Dept have the same lifespans. In Section 4.1.1, we will use lifespans to formulate a Lifespan Decomposition Rule. The importance of lifespans in temporal databases has been recognized in the context of data models in the past. In the HRDM model, Clifford [CT85, CC87, CC93] associates explicit lifespans with each attribute of a relation schema and with each tuple of a relation instance. The HRDM goes further than other data models in incorporating lifespans, but it still does not explicitly record the lifespans of attributes of individual ....

....means of identifying this type of redundancy. Note that patterns with additional time points are also consistent with the instance. For example, the salary may have been updated to become 50k at time 55. ut This type of redundancy has been mentioned in the past by several researchers (see, e.g. CT85, CV85, Gad88, GY91] Most often, it has been used for motivating a non first normal form data modeling approach where time is associated with with attribute values rather than with tuples, because that approach avoids the redundancy. The empDepSal instance is given next in a typical non first ....

J. Clifford and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In Proceedings of ACM SIGMOD, pages 247--265, Austin, TX, May 1985.

....world, but also its previous and possibly future states. Temporal languages must handle the temporal aspects of data accordingly. In recent years several temporal data models and languages have been developed. Examples for temporal relational data models and corresponding temporal languages are [1, 2,3,4,5,6,7,8,9]. Most of the temporal database languages are extensions of traditional textual database languages, e.g. SQL. Therefore the extended syntax and semantics of temporal languages is even harder to learn than for traditional (non temporal) languages. Users have to know the syntax and semantics of the ....

J. Clifford, A. U. Tansel. On an algebra for historical relational databases: two views. In S. Navathe (Ed.), Proc. of the ACM-SIGMOD International Conference on Management of Data, pp. 247-265, Austin, Texas, 1985.

....a common temporal query language [S 94] The infrastructure work forms a basis for temporal technology development, such that additional functionality can be incorporated either through mapping to or augmentation of such infrastructure. Following these works, we adopt a discrete model of time [CT85] which is isomorphic to the natural numbers. In this paper we use the following terms: Definition 1.1 Chronon [JCG 92] is a nondecomposable unit of time, whose granularity is application dependent. In our case study we use the composition of date;hh:mm (date, hour and minute) to designate a ....

J. Clifford and A. U. Tansel. On an algebra for historical relational databases: two views. In Proceedings of the ACM SIGMOD, pages 247--265, May 1985.

....model deviates from this tradition. Rather, these models have been presented as a set of formulae some of which are ground, but others of which have included one or more free, current time variables. Chief among these current time variables is now (e.g. Clifford and Croker 1987, Gadia 1988, Clifford and Tansel 1985] but a variety of other symbols have been used, including [Ben Zvi 1982] 1 [Snodgrass 1987] Lorentzos and Johnson 1988] and until changed [Wiederhold et al. 1993] As already mentioned and exemplified, the use of such variables is quite convenient and practical. Thus, these ....

J. Clifford and A. U. Tansel. On an algebra for historical relational databases: Two views. In Proceedings of ACM SIGMOD International Conference on Management of Data, S. Navathe, editor, pp. 247--265, Austin, TX, May 1985.

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J. Cli#ord and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In S. Navathe, editor, In Proceeding of ACM SIGMOD, pages 247--265, Austin, TX, May 1985.

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J. Clifford and A. U. Tansel. On an Algebra for Historical Relational Databases: Two Views. In Proceedings of ACM SIGMOD, pages 247--265, Austin, TX, May1ff

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J. Clifford and A.U. Tansel, "On an Algebra for Historical Relational Databases: Two Views," in Proceedings of the ACM SIGMOD International Conference on Management of Data, S. Navathe (ed.), Austin, TX, 247--265, 1985.

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J. Clifford and A. Tansel. On An Algebra for Historical Relational Databases: Two Views. In Proceedings International Conference on Management of Data, pages 247--265, Austin, Texas, 1985.

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J. Cli#ord, A.U. Tansel, #On an Algebra for Historical Relational Database: Two Views," Proc. ACM SIGMOD Conf., pp. 247#265, 1985.

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