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On the Semantics of

TL;DR: Two new types of modelling entities that address situations where the existing time variables are inadequate are introduced and defined within the framework, which provides a foundation, using algebraic bind operators, for the querying of variable databasesvia existing query languages.
Abstract: While "now" is expressed in SQL as CURRENT-TIMESTAMP within queries, this value cannot bestored in the database. However, this notion of an ever-increasing current-time value has beenreflected in some temporal data models by inclusion of database-resident variables, such as"now," "until-changed," "∞," "@" and "-." Time variables are very desirable, but their usealso leads to a new type of database, consisting of tuples with variables, termed a variabledatabase.This paper proposes a framework for defining the semantics of the variable databases of temporalrelational data models. A framework is presented because several reasonable meaningsmay be given to databases that use some of the specific temporal variables that have appearedin the literature. Using the framework, the paper defines a useful semantics for such databases.Because situations occur where the existing time variables are inadequate, two new types ofmodeling entities that address these shortcomings, timestamps which we call now-relative andnow-relative indeterminate, are introduced and defined within the framework. Moreover, the paperprovides a foundation, using algebraic bind operators, for the querying of variable databasesvia existing query languages. This transition to variable databases presented here requires minimalchange to the query processor. Finally, to underline the practical feasibility of variabledatabases, we show that database variables can be precisely specified and efficiently implementedin conventional query languages, such as SQL, and in temporal query languages, suchas TSQL2.
Citations
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Journal Article
TL;DR: This work identifies a Semantic Technology that supports the key capabilities also needed to realize the Semantic Web vision, namely representing, acquiring and utilizing knowledge.
Abstract: Semantics is seen as the key ingredient in the next phase of the Web infrastructure as well as the next generation of information systems applications. In this context, we review some of the reservations expressed about the viability of the Semantic Web. We respond to these by identifying a Semantic Technology that supports the key capabilities also needed to realize the Semantic Web vision, namely representing, acquiring and utilizing knowledge. Given that scalability is a key challenge, we briefly review our observations from developing three classes of real world applications and corresponding technology components: search/browsing, integration, and analytics. We distinguish this proven technology from some parts of the Semantic Web approach and offer subjective remarks which we hope will foster additional debate.

352 citations


Cites background from "On the Semantics of"

  • ...The issue of the current positions, or the NOW positions is challenging [ 10 ]....

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Proceedings ArticleDOI
23 Mar 1999
TL;DR: The paper presents nine requirements to multidimensional data models, each of which is exemplified by a real world, clinical case study, and defines an extended multiddimensional data model, and an associated algebra, which address all nine requirements.
Abstract: Online Analytical Processing (OLAP) systems considerably ease the process of analyzing business data and have become widely used in industry. Such systems primarily employ multidimensional data models to structure their data. However current multidimensional data models fall short in their abilities to model the complex data found in some real world application domains. The paper presents nine requirements to multidimensional data models, each of which is exemplified by a real world, clinical case study. A survey of the existing models reveals that the requirements not currently met include support for many-to-many relationships between facts and dimensions, built-in support for handling chance and time, and support for uncertainty as well as different levels of granularity in the data. The paper defines an extended multidimensional data model, and an associated algebra, which address all nine requirements.

230 citations


Cites methods from "On the Semantics of"

  • ...For the “Valid To” attribute, we use the special, continously-growing value “NOW” that denotes the current time [ 20 ]....

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Book ChapterDOI
01 Jan 2000
TL;DR: This Chapter also contains a discussion on operational semantics of the generally too abstract notion of membership function and a survey of variants of fuzzy sets and related matters.
Abstract: This paper is an introduction to fuzzy set theory. It has several purposes. First, it tries to explain the emergence of fuzzy sets from an historical perspective. Looking back to the history of sciences, it seems that fuzzy sets were bound to appear at some point in the 20th century. Indeed, Zadeh’s works have cristalized and popularized a concern that has appeared in the first half of the century, mainly in philosophical circles. Another purpose of the paper is to scan the basic definitions in the field, that are required for a proper reading of the rest of the volume, as well as the other volumes of the Handbooks of Fuzzy Sets Series. This Chapter also contains a discussion on operational semantics of the generally too abstract notion of membership function. Lastly, a survey of variants of fuzzy sets and related matters is provided.

201 citations

Journal Article
TL;DR: This paper builds on an understanding of services and their interactions, to outline the non-functional properties of Services and their uses.
Abstract: A proper understanding of the general nature, potential and obligations of electronic services may be achieved by examining existing commercial services in detail. The everyday services that surround us, and the ways in which we engage with them, are the result of social and economic interaction that has taken place over a long period of time. If we attempt to provide electronic services, and do not take this history into account, then we will fail. Any attempt to provide automated electronic services that ignores this history will deny consumers the opportunity to negotiate and refine, over a large range of issues, the specific details of the actual service to be provided. To succeed, we require a rich and accurate means of representing services. An essential ingredient of service representation is capturing the non-functional properties of services. These include the methods of charging and payment, the channels by which the service is requested and provided, constraints on temporal and spatial availability, service quality, security, trust and the rights attached to a service. Not only are comprehensive descriptions essential for useful service discovery, they are also integral to service management, enabling service negotiation, composition, and substitution. This paper builds on an understanding of services and their interactions, to outline the non-functional properties of services and their uses.

168 citations


Cites methods from "On the Semantics of"

  • ...A useful summary of the problems associated with using temporal time stamps such as now are outlined in [ 14 ]....

    [...]

Journal ArticleDOI
TL;DR: Although “Now” is expressed in SQL and CURRENT_TIMESTAMP within queries, this value cannot be stored in the database, and the notion of an ever-increasing current-time value has been reflected in some temporal data models by inclusion of database-resident variables.
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.

161 citations