article

Free access

On the semantics of “now” in databases

Editor: Won Kim Authors:

Richard Thomas SnodgrassAuthors Info & Claims

ACM Transactions on Database Systems (TODS), Volume 22, Issue 2

Pages 171 - 214

https://doi.org/10.1145/249978.249980

Published: 01 June 1997 Publication History

PDF eReader

Abstract

Although “now” is expressed in SQL and CURRENT_TIMESTAMP within queries, this value cannot be stored in the database. How ever, this notion of an ever-increasing current-time value has been reflected in some temporal data models by inclusion of database-resident variables, such as “now” “until-changed, ” “**,” “@,” and “-”. Time variables are very desirable, but their used also leads to a new type of database, consisting of tuples with variables, termed a variable database.

References

[1]

AL-TAHA, K. K., SNODGRASS, R. T., AND Soo, M.D. 1994. Bibliography on spatiotemporal databases. Int. J. Geograph. Inf. Syst. 8, 1 (Jan.-Feb.), 95-103.

Google Scholar

[2]

ARIAV, G., BELLER, A., AND MORGAN, H.L. 1984. A temporal data model. Tech. Rep. DS-WP 82-12-05, Decision Sciences Dept., Univ. of Pennsylvania, Dec.

Google Scholar

[3]

BASSIOUNI, M. A. AND LLEWELLYN, M. J. 1992. A relational-calculus query language for historical databases. Comput. Lang. 17, 3, 185-197.

Digital Library

Google Scholar

[4]

BEN-ZvI, J. 1982. The time relational model. Univ. of California at Los Angeles, Ph.D. Thesis.

Digital Library

Google Scholar

[5]

BHARGAVA, G. AND GADIA, S. 1989. Achieving zero information loss in a classical database environment. In Proceedings of the International Conference on Very Large Databases (Amsterdam, Aug.), 217-224.

Digital Library

Google Scholar

[6]

BRUSONI, V., CONSOLE, L., TERENZIANI, P., AND PERNICI, B. 1995. Extending temporal relational databases to deal with imprecise and qualitative temporal information. In Proceedings of the VLDB International Workshop on Temporal Databases (Zurich, Switzerland, Sept.), J. Clifford and A. Tuzhilin (Eds), Workshops in Computing Series, Springer Verlag, New York, NY, 3-22.

Digital Library

Google Scholar

[7]

CLIFFORD, J. 1993. Indexical databases. In Advanced Database Systems, Lecture Notes in Computer Science 759, Springer-Verlag.

Digital Library

Google Scholar

[8]

CLIFFORD, J. AND CROKER, A. 1987. The historical relational data model HRDM and algebra based on lifespans. In Proceedings of the IEEE International Conference on Data Engineering (Los Angeles, CA, Feb.), 528-537.

Digital Library

Google Scholar

[9]

CLIFFORD, J., CROKER, A., AND TUZHILIN, A. 1993. On completeness of historical relational query languages. ACM Trans. Database Syst. 19, 2 (March), 64-116.

Digital Library

Google Scholar

[10]

CLIFFORD, J., DYRESON, C. E., ISAKOWITZ, T., JENSEN, C. C., AND SNODGRASS, R.T. 1994. On the semantics of'now' in temporal databases. Tech. Rep. R-94-2047, Aalborg Univ., Dept. of Mathematics and Computer Science, Denmark, Nov.

Google Scholar

[11]

CLIFFORD, g. AND ISAKOWITZ, T. 1993. On the semantics of transaction time and valid time in bitemporal databases. In Proceedings of the ARPA/NSF International Workshop on an Infrastructure for Temporal Databases (Arlington, TX, June), R. T. Snodgrass, Ed., 1.1-I.17.

Google Scholar

[12]

CLIFFORD, J. AND ISAKOWITZ, T. 1994. On the semantics of (bi)temporal variable databases. In Proceedings of the Fourth International Conference on Extending Database Technology (Cambridge, England, March), 215-230.

Digital Library

Google Scholar

[13]

CLIFFORD, J. AND TANSEL, A.U. 1985. On an algebra for historical relational databases: Two views. In Proceedings of ACM SIGMOD International Conference on Management of Data, S. Navathe, Ed., (Austin, TX, May), 247-265.

Digital Library

Google Scholar

[14]

CLIFFORD, J. AND WARREN, D.S. 1983. Formal semantics for time in databases. ACM Trans. Database Syst. 8, 2, 214-254.

Digital Library

Google Scholar

[15]

CODD, E.F. 1970. A relational model of data for large shared data banks. Commun. ACM 13, 6 (June), 377-387.

Digital Library

Google Scholar

[16]

DATE, C. J. AND WHITE, C. J. 1990. A Guide to DB2, Vol. 1, 3rd ed. Addison-Wesley, Reading, MA.

Google Scholar

[17]

DUTTA, S. 1989. Generalized events in temporal databases. In Proceedings of the Fifth International Conference on Data Engineering, (Los Angeles, CA, Feb.), 118-126.

Digital Library

Google Scholar

[18]

DYRESON, C.E. 1994. Valid-time indeterminacy. Computer Science Dept., Univ. of Arizona. Ph.D. Thesis, Oct.

Digital Library

Google Scholar

[19]

DYRESON, C. E. AND SNODGRASS, R.T. 1993a. Timestamp semantics and representation. Inf. Syst. 18, 3, 143-166.

Digital Library

Google Scholar

[20]

DYRESON, C. E. AND SNODGRASS, R.T. 1993b. Valid-time indeterminacy. In Proceedings of the International Conference on Data Engineering (Vienna, Austria, April), 335-343.

Digital Library

Google Scholar

[21]

DYRESON, C. E. AND SNODGRASS, R.T. 1993c. A timestamp representation. In The TSQL Temporal Query Language, R. T. Snodgrass, Ed., Kluwer, Boston, MA, 1995, Chap. 25, 475-499.

Google Scholar

[22]

ELMASRI, R., Wuu, G., AND KIM, Y. 1990. The time index--an access structure for temporal data. In Proceedings of the International Conference on Very Large Data Bases (Brisbane, Australia, Aug.), 1-12.

Digital Library

Google Scholar

[23]

FINGER, M. 1992. Handling database updates in two-dimensional temporal logic. J. Appl. Non-Classical Logics 2, 2.

Crossref

Google Scholar

[24]

FRAENKEL, A. A., BAR-HILLEL, Y., AND LEVY, A. 1973. Foundations of Set Theory. North- Holland, Amsterdam, Netherlands.

Google Scholar

[25]

GADIA, S. K. 1988. A homogeneous relational model and query languages for temporal databases. ACM Trans. Database Syst. 13, 4 (Dec.), 418-448.

Digital Library

Google Scholar

[26]

GADIA, S. AND NAIR, S. 1993. Temporal databases: A prelude to parametric data. In Temporal Databases: Theory, Design, and Implementation, A. Tansel et al., Eds., Benjamin Cummings, Redwood City, CA, Chap. 2, 28-66.

Google Scholar

[27]

GADIA, S. K., NAIR, S., AND POON, Y.-C. 1992. Incomplete information in relational temporal databases. In Proceedings of the Conference on Very Large Data Bases (Vancouver, Canada, Aug.).

Digital Library

Google Scholar

[28]

JENSEN, C. S. AND MARK, L. 1990. A framework for vacuuming temporal databases. Tech. Rep. CS-TR-2516/UMIACS-TR-90-105, Univ. of Maryland, Dept. of Computer Science, College Park, MD, Aug.

Digital Library

Google Scholar

[29]

JENSEN, C. S. AND MARK, L. 1992. Queries on change in an extended relational model. IEEE Trans. Knowl. Data Eng. 4, 2 (April), 192-200.

Digital Library

Google Scholar

[30]

JENSEN, C. S. AND SNODGRASS, R.T. 1992. Temporal specialization. In Proceedings of the IEEE International Conference on Data Engineering (Tempe, AZ, Feb.), 594-603.

Digital Library

Google Scholar

[31]

JENSEN, C. S. AND SNODGRASS, R.T. 1994. Temporal specialization and generalization. IEEE Trans. Knowl. Data Eng. 6, 6 (Dec.), 954-974.

Digital Library

Google Scholar

[32]

JENSEN, C. S. AND SNODGRASS, R.T. 1996. Semantics of time-varying information. Inf. Syst. 21, 4, 311-352.

Digital Library

Google Scholar

[33]

JENSEN, C. S., CLIFFORD, J., ELMASRI, R., GADIA, S. K., HAYES, P., AND JAJODIA, S. (EDS.) 1994. A consensus glossary of temporal database concepts. ACM SIGMOD Rec., 23, 1 (March), 52-65.

Digital Library

Google Scholar

[34]

JENSEN, C. S., Soo, M. D., AND SNODGRASS, R.T. 1994. Unifying temporal data models via a conceptual model. Inf. Syst. 19 7 (Dec.), 513-547.

Digital Library

Google Scholar

[35]

KURUTACH, W. AND FRANKLIN, g. 1993. On temporal-fuzziness in temporal fuzzy databases. In DEXA'93 (Prague, Czech Republic, Sept.), 154-165.

Digital Library

Google Scholar

[36]

LIPSKI, W. JR. 1979. On semantic issues connected with incomplete information databases. ACM Trans. Database Syst. 4, 3 (Sept.), 262-296.

Digital Library

Google Scholar

[37]

LORENTZOS, N. A. AND JOHNSON, R. G. 1988. Extending relational algebra to manipulate temporal data. Inf. Syst. 13, 3, 286-296.

Digital Library

Google Scholar

[38]

MELTON, J. AND SIMON, A. R. 1993. Understanding the New SQL: A Complete Guide. Morgan-Kaufmann, San Mateo, CA.

Digital Library

Google Scholar

[39]

MONTAGUE, R. 1974. Formal Philosophy: Selected Papers of Richard Montague. Yale University Press, New Haven, CT.

Google Scholar

[40]

NAVATHE, S. B. AND AHMED, R. 1989. A temporal relational model and a query language. Inf. Sci. 49, 147-175.

Digital Library

Google Scholar

[41]

REITER, R. 1984. Towards a logical reconstruction of relational database theory. In On Conceptual Modelling, Springer Verlag, New York, 191-233.

Google Scholar

[42]

RODDICK, g.F. 1992. Schema evolution in database systems--An annotated bibliography. SIGMOD Rec. 21, 4 (Dec.), 35-40.

Digital Library

Google Scholar

[43]

SARDA, N.L. 1990. Algebra and query language for a historical data model. Computer J., 33, 1 (Feb.), 11-18.

Digital Library

Google Scholar

[44]

SNODGRASS, R.T. 1987. The temporal query language TQuel. ACM Trans. Database Syst. 12, 2 (June), 247-298.

Digital Library

Google Scholar

[45]

SNODGRASS, R.T. 1993. An overview of TQuel. In Temporal Databases: Theory, Design, and Implementation, A. Tansel et al., Eds., Benjamin-Cummings, Redwood City, CA, Chap. 6, 141-182.

Google Scholar

[46]

SNODGRASS, R. T. (ED.) 1995. The TSQL2 Temporal Query Language. Kluwer, Boston, MA.

Digital Library

Google Scholar

[47]

SNODGRASS, R. T. AND AHN, I. 1985. A taxonomy of time in databases. In Proceedings of ACM SIGMOD International Conference on Management of Data (Austin, TX, May), 236- 246.

Digital Library

Google Scholar

[48]

SYKES, J. B. (ED.) 1964. The Concise Oxford Dictionary. Oxford University Press, Oxford, England.

Google Scholar

[49]

TANSEL, A.U. 1990. Modelling temporal data. Inf. Sofw. Technol. 32, 8 (Oct.), 514-520.

Digital Library

Google Scholar

[50]

TANSEL, A., CLIFFORD, J., GADIA, S., JAJODIA, S., SEGEV, A., AND SNODGRASS, R. T. (EDS.) 1993. Temporal Databases: Theory, Design, and Implementation. Benjamin-Cummings, Redwood City, CA.

Digital Library

Google Scholar

[51]

THIRUMALAI, S. AND KRISHNA, S. 1988. Data organization for temporal databases. Tech. Rep., Raman Research Institute, Bangalore, India.

Google Scholar

[52]

WIEDERHOLD, G., JAJODIA, S., AND LITWIN, W. 1993. Integrating temporal data in a heterogeneous environment. In Temporal Databases: Theory, Design, and Implementation. Benjamin-Cummings, Redwood City, CA, 563-579.

Google Scholar

[53]

YAU, C. AND CHAT, G. S.W. 1991. TempSQL--A language interface to a temporal relational model. Inf. Sci. Tech. (Oct.), 44-60.

Google Scholar

Cited By

View all

Dyreson CShatnawi ABhowmick SSharma V(2024)Temporal JSON Keyword SearchProceedings of the ACM on Management of Data10.1145/36549802:3(1-27)Online publication date: 30-May-2024
https://dl.acm.org/doi/10.1145/3654980
Brahmia ZGrandi FOliboni B(2024)Schema Versioning in Databases: A Literature ReviewComputing Open10.1142/S2972370124300024Online publication date: 18-Oct-2024
https://doi.org/10.1142/S2972370124300024
Reznichenko V(2021)60 Years of Databases (part two)PROBLEMS IN PROGRAMMING10.15407/pp2021.04.036(036-061)Online publication date: Dec-2021
https://doi.org/10.15407/pp2021.04.036
Show More Cited By

Index Terms

On the semantics of “now” in databases
1. Information systems
  1. Data management systems
    1. Database management system engines
      1. Database query processing
    2. Query languages
2. Theory of computation
  1. Theory and algorithms for application domains
    1. Database theory
      1. Database query languages (principles)
      2. Database query processing and optimization (theory)

Recommendations

Modification semantics in now-relative databases

Most real-world databases record time-varying information. In such databases, the notion of "the current time," or NOW, occurs naturally and prominently. For example, when capturing the past states of a relation using begin and end time columns, tuples ...
Supporting valid-time indeterminacy

In valid-time indeterminacy it is known that an event stored in a database did in fact occur, but it is not known exactly when. In this paper we extend the SQL data model and query language to support valid-time indeterminacy. We represent the occurrence ...
Extending the View Updatability of Relational Databases from Set Semantics to Bag Semantics and Its Implementation on PostgreSQL
IMCOM '18: Proceedings of the 12th International Conference on Ubiquitous Information Management and Communication

View support is one of the most attractive features of relational databases from both theoretical and practical points of view. However, as views are not base relations stored in a database but merely definitions of queries issued to a database, the ...

Reviews

Reviewer: Julia E. Hodges

In many database applications, the ability to represent certain concepts of time, such as “this information is valid now ” or “this information is valid until changed, ” is important. The authors refer to databases that include current-time variables as “variable databases.” In this paper, they provide a framework for defining the semantics of variable databases. They also introduce “now-relative” and “now-relative indeterminate” timestamps as ways of modeling current-time variables. They motivate their work with examples that illustrate the need for more than one meaning of the variable now. The authors' framework for defining the semantics of variable databases is presented “in terms of databases of a fully extensional temporal data model.” In this approach, there are well-defined mappings between each of three distinct time dimensions (valid time, transaction time, and reference time) and its temporal universe. Thus, there are three temporal universes in the framework. The semantics of a variable database is specified in terms of an extensionalization mapping. The authors provide formal definitions of the terms used in their framework. The formality makes the paper more suited for researchers with a specific interest in temporal databases than for a more general audience. However, the authors have also provided a number of practical examples to illustrate the terms, which makes the paper more readable than many theoretical papers. Their use of graphs for the visualization of tuples in a variable database also makes their framework more understandable.

Access critical reviews of Computing literature here

Become a reviewer for Computing Reviews.

Comments

Please enable JavaScript to view thecomments powered by Disqus.

Information & Contributors

Information

Published In

cover image ACM Transactions on Database Systems

ACM Transactions on Database Systems Volume 22, Issue 2

June 1997

200 pages

ISSN:0362-5915

EISSN:1557-4644

DOI:10.1145/249978

Editor:
Won Kim
UniSQL, Inc., Austin, TX

Issue’s Table of Contents

Publisher

Association for Computing Machinery

New York, NY, United States

Publication History

Published: 01 June 1997

Published in TODS Volume 22, Issue 2

Permissions

Request permissions for this article.

Request Permissions

Check for updates

Author Tags

Qualifiers

Article

Contributors

Other Metrics

View Article Metrics

Bibliometrics & Citations

Bibliometrics

Article Metrics

118
Total Citations
View Citations
1,161
Total Downloads

Downloads (Last 12 months)110
Downloads (Last 6 weeks)22

Reflects downloads up to 20 Jan 2025

Other Metrics

View Author Metrics

Citations

Cited By

View all

Dyreson CShatnawi ABhowmick SSharma V(2024)Temporal JSON Keyword SearchProceedings of the ACM on Management of Data10.1145/36549802:3(1-27)Online publication date: 30-May-2024
https://dl.acm.org/doi/10.1145/3654980
Brahmia ZGrandi FOliboni B(2024)Schema Versioning in Databases: A Literature ReviewComputing Open10.1142/S2972370124300024Online publication date: 18-Oct-2024
https://doi.org/10.1142/S2972370124300024
Reznichenko V(2021)60 Years of Databases (part two)PROBLEMS IN PROGRAMMING10.15407/pp2021.04.036(036-061)Online publication date: Dec-2021
https://doi.org/10.15407/pp2021.04.036
Mukhitova AYerimbetova AMladenovic N(2021)XML Document Transformation for Data Manipulation Operations2021 6th International Conference on Computer Science and Engineering (UBMK)10.1109/UBMK52708.2021.9559019(592-597)Online publication date: 15-Sep-2021
https://doi.org/10.1109/UBMK52708.2021.9559019
Debrouvier AParodi EPerazzo MSoliani VVaisman A(2021)A model and query language for temporal graph databasesThe VLDB Journal — The International Journal on Very Large Data Bases10.1007/s00778-021-00675-430:5(825-858)Online publication date: 12-May-2021
https://dl.acm.org/doi/10.1007/s00778-021-00675-4
Mulle YBohlen M(2020)Query Results over Ongoing Databases that Remain Valid as Time Passes By2020 IEEE 36th International Conference on Data Engineering (ICDE)10.1109/ICDE48307.2020.00127(1429-1440)Online publication date: Apr-2020
https://doi.org/10.1109/ICDE48307.2020.00127
Brahmia ZHamrouni HBouaziz R(2020)XML data manipulation in conventional and temporal XML databases: A surveyComputer Science Review10.1016/j.cosrev.2020.10023136(100231)Online publication date: May-2020
https://doi.org/10.1016/j.cosrev.2020.100231
Brahmia SBrahmia ZGrandi FBouaziz R(2019)A Disciplined Approach to Temporal Evolution and Versioning Support in JSON Data StoresEmerging Technologies and Applications in Data Processing and Management10.4018/978-1-5225-8446-9.ch006(114-133)Online publication date: 2019
https://doi.org/10.4018/978-1-5225-8446-9.ch006
Anselma LPiovesan LStantic BTerenziani P(2018)Representing and querying now-relative relational medical dataArtificial Intelligence in Medicine10.1016/j.artmed.2018.01.00486:C(33-52)Online publication date: 1-Mar-2018
https://dl.acm.org/doi/10.1016/j.artmed.2018.01.004
Lomet D(2018)Supporting Transaction Time DatabasesEncyclopedia of Database Systems10.1007/978-1-4614-8265-9_381(3857-3862)Online publication date: 7-Dec-2018
https://doi.org/10.1007/978-1-4614-8265-9_381
Show More Cited By

View Options

View options

PDF

View or Download as a PDF file.

PDF

eReader

View online with eReader.

eReader

Login options

Check if you have access through your login credentials or your institution to get full access on this article.

Abstract

References

Cited By

Index Terms

Recommendations

Modification semantics in now-relative databases

Supporting valid-time indeterminacy

Extending the View Updatability of Relational Databases from Set Semantics to Bag Semantics and Its Implementation on PostgreSQL

Reviews

Access critical reviews of Computing literature here

Comments

Information

Published In

Publisher

Publication History

Permissions

Check for updates

Author Tags

Qualifiers

Contributors

Other Metrics

Bibliometrics

Article Metrics

Other Metrics

Citations

Cited By

View options

PDF

eReader

Login options

Full Access

Figures

Other

Share

Share this Publication link

Share on social media

Affiliations