Showing papers by "Ramez Elmasri published in 1993"

A Temporal Model and Query Language for EER Databases.

Abstract: A temporal extension to an extended ER (entity-relationship) model is proposed. The concept of life span for entities and relationships is incorporated in the ER model. Also specified is a temporal query and update language which is an extension of the GORDAS language. The concepts of temporal Boolean expressions, temporal selection, and temporal projection are introduced, and their use in the query language is illustrated. Temporal constraints are incorporated into the ER model, and the semantics of temporal update operations is defined.<>

Temporal database modeling: an object-oriented approach

Abstract: This work proposes a number of different approaches for incorporating temporal extensions to object-oriented databases. One important question that arises when dealing with temporal databases in the context of objec&oriented systems is whether to associate time with objects or with attributes. Results of previous work comparing tuple (ob ject) versioning and attribute versioning — such as whether to extend flat (F’NF) or nested (NF’NF) relational models — are not applicable to temporal object-oriented databases. This is because object-oriented models provide more powerful constructs than traditional modeis for structuring complex objects. Our goal in this paper is to study alternative temporal object-oriented database representations by identifying the different techniques for representing temporal databases in an object-riented framework. This is in contrast to other work that adopts a single particular approach. Our goal is to determine the particular situation for which each repr~ sentation is applicable. We define the concepts of object versioning and attribute versioning in temporal object-oriented models, and we concentrate on identifying the various representations of temporal relationships between objects. Another contribution of this paper is to analyze our different temporal representations and to determine their storage requirement. A general framework is defined in which the characteristics of various temporal models are studied. A simulation study is performed comparing storage costs of our various temporal representations, and also a temporal FNF relational representation. * Computer Science Engineering Department ,The University of Texas at Arlington, Arlington, Texas 76019, Fax: (817) 2733784, Telephone: (817) 273-3785, Email: ehnasri@cse.uta.edu. t Office Of The Vice President for Resemch & Information Technology, Rice University, P.O. Box 1892, Houston, Texas 77251, Fax: (713) 523-0259, Telephone: (713) 523-0080, Email: vram@rice .edu. This work was done while the author was *ociated with The University of Texas at Arlington. ~ Computer Science Engineering Department ,The University of Texas at Arlington, Arlington, Texas 76019, Fax: (817) 2733784, Telephone: (81 7) 2733785, Email: fernando@cse.uta.edu. Permission to copy without fee afl or pwt of this material is grantad providatf that tho copies aro not made or cfistributad for direct commercial advantaga, tha ACM cop~ight notico ●nd tha titla of the publication and ita date appeor, ●nd notice is @ven that copying ia by parmkion of tha Association for Computing Machinary. 10 copy otherwise, or to rapublish, requires a faa arrdlor specific permission. CIKM ’93-1 l/93/O. C., USA @ 1993 ACM 0-89791-626-3/93/001 1 .. ..$1.50

Automatic class and method generation for object-oriented databases

Abstract: Several approaches have been taken to incorporate integrity constraints into the class definitions of an object-oriented (OO) database. In this work, we generate constraint checks automatically in the basic methods of a class definition. The constraints are derived from the Extended Entity-Relationship (EER) model, and incorporated into the object-oriented classes. Our work investigates the issues in designing an OO database by mapping an EER[1] schema into an Object model[2]. We define a number of basic methods for each class, and automatically generate default class definitions including both attributes and basic methods. In our approach, the constraints are incorporated into the code of the basic methods for each object class.

A Temporal Query Language For A Conceptual Model

Abstract: This chapter was a summary of our work in temporal conceptual models and query languages [173, 178, 174, 179], Our model distinguishes between conceptual and temporal objects, and characterizes the properties of entities (conceptual objects), entity roles (temporal objects), and (temporal and non-temporal) attributes. It also defines temporal constraints among entity roles, differentiates between temporal and conceptual relationships, and provides rules for preserving temporal integrity constraints.

Adaptive transaction scheduling

Abstract: Transaction scheduling is necessary to downgrade concurrency control insensitivity to both data and resource contention. W bile resource contention can be relieved by employing adclitioual MIPS processing power and memory space, data contention remains inevitable especially in high-speed on-line transaction processing systems, or in databases with hot-spots. We define two main objectives for transaction scheduling. The first is to maximize the effective level of concurrency, which excludes concurrency contributeci by unsuccessful transactions. The aim here is to increase throughput or transactions per second (TPS). The second objective is the timely detection and handling of highly contentious data items as well as highly contending transactions. To achieve this objective we use adaptable back-off strategies to restart and delay contending transactions. The same strategies are used to distance concurrent accesses to hot spots. In this paper we present an adaptable transaction scheduling technique that is applicable to high contention environments, and that can be used in conjunction with any lock-based concurrency control algorithm. We show how we attempt to achieve optiruum performance over a wide range of conflict levels, where depending on various criteria, transactions are scheduled for execution, delayed, or backed-off. We describe a simulation-based performance study of transaction scheduling and its impact on various concurrency control algorithms.