Vram Kouramajian

The time index + : an incremental access structure for temporal databases

1 Introduction In this paper, we propose a new indexing structure, called the Time Index+, which extends the incremental structure techuique introduced in the Time Index [E1WK90, Kour94]. The Time Index performs well for data that often overlaps and has a non– uniform distribution. However, it requires huge amounts of storage aud suffers from degradation in update p erformauce. The Time Index+ overcomes the deficiencies of the Time Index by proposing au efficient new storage model for partitioning logical buckets and by suggesting a graceful new method for handling object versions with long and very long time intervals. We validate our claims for the efficiency of our new tectilques by analyzing and comparing four indexing structures: the Time Index+, the Time Index, the Packed R-Tree [RoLe85, KaFa93], and the Parametrized R–Tree. Our experiments identify impor-taut parameters, and show how they affect the performance of the four considered indexing structures. These include meau of version lifespan, block size, query time intervaf length, aud total number of versions. Our simulation results show that: (1) The Time Index+ pre vides au improvement in searck time of 10~o over the Time Index, of au order of magnitude over the Packed R–Tree, and of at least 100~0 over the Parametrized R–Tree and (2) The Time Iudex+ requires on average 60~0 less storage than the the Time Index but 51)~o more storage than the Packed R–Tree and the Parametrized R–Tree. Permission to co y without fee all or part of this material is F granted provided t at the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association of Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. Temporal databases support both valid tin e, which records a history of changes in the real world, rmd transaction time, wh,ch records a hktory of updates made to the database. This permits users to query over the complete history of a given Universe of Discourse. However, the incorporation of time in database models has a profound impact on every facet of database implementation. An important facet that requires a complete re–evaluation is indexing techniques aud search methods, which is the topic of this paper. Current trends suggest that database systems will need to manage ever–larger volumes …

Experience with the virtual notebook system: abstraction in hypertext

The Virtual Notebook System (VNS) is a distributed collaborative hypertext system that has made a successful transition from research prototype to commercial product. Experience in developing and deploying the VNS in diverse settings including biomedical research, undergraduate education, and collaborative system prototyping has developed insight into the use of systems for computer-supported cooperative work (CSCW). This paper provides a brief overview of the VNS, discusses some of its strengths and weaknesses with respect to collaboration, and draws some conclusions about the impact of metaphor and extensibility on the collaborative process.

Partitioning of time index for optical disks

The authors present a storage model for temporal databases that accommodates large amounts of temporal data. The model supports efficient search for object versions based on temporal conditions, using a time index. They define an access structure, the monotonic B/sup +/-tree, that is suitable for implementing a time index for append-only temporal databases. The storage model uses a combination of magnetic disks and write-once optical disks to keep current, past, and even future states of a database online and readily accessible. It provides an automatic archiving of both object versions and time index blocks to optical disks.<<ETX>>

Temporal database modeling: an object-oriented approach

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 .. ..

Declustering techniques for parallelizing temporal access structures

1.50

A Temporal Query Language For A Conceptual Model

This paper addresses the issues of declustering temporal index and access structures for a single processor multiple independent disk architecture. The temporal index is the Monotonic B/sup +/-Tree which uses the time index temporal access structure. We devise a new algorithm, called multi-level round robin, for assigning tree nodes to multiple disks. The multi-level round robin declustering technique takes advantage of the append-only nature of temporal databases to achieve uniform load distribution, decrease response time, and increase the fanout of the tree by eliminating the need to store disk numbers within the tree nodes. We propose two declustering techniques for the time index access structures; one considers only time proximity while declustering, whereas the other considers both time proximity and data size. We investigate their performance over different types of temporal queries and show that various temporal queries have conflicting allocation criteria for the time index buckets. In addition, we devise two disk partition techniques for the time index buckets. The mutually exclusive technique partitions the disks into disjoint groups, whereas the shared disk technique allows the different types of buckets to share all disks.<<ETX>>

Automatic class and method generation for object-oriented databases

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.

Consortium: a framework for transactions in collaborative environments

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 Based on Conceptual Entities and Roles

We introduce a natural and flexible framework for collaborative transactions called Consortium. We also define a new model for collaborative interaction that we call “What You See Is What You Want” ( WYSIWYW), an abstraction that permits users to choose their own interaction modes with respect to the shared workspace. Consortium is not an extension to the transaction model but rather a flexible framework for defining collaborative transactions. The contribution of this work is a framework for collaborative transactions that allows a transaction to: (1) support the abstraction of WYSIWYW’, (2) span mtdtiple sessions, (3) have multiple commit points, (4) have different participants at different times, and (5) differentiate between the concepts of owners and participants. In addition, this paper defines the concept of transaction leasing, identifies policies for joining, leaving, and participating in a transaction, extends the notion of transaction ownership by allowing ownership transfer, and describes mechanisms for sharing locks in collaborative transactions.

The Design and Evaluation of a Magnetic/Optical Access Structure for Temporal Databases

In our previous work [EIEK90], we introduced a Semantic Temporal model based on the Extended Entity-Relationship model (STEER), where we proposed new classification concepts for temporal/conceptual objects and relationships. We defined temporal constraints and outlined rules for preserving temporal integrity constraints.