DATABASE APPROACH FOR MULTIPLE-CRITERIA DECISION SUPPORT SYSTEMS

This paper focuses on data management aspects of computerized decision support systems which use interactive multiple criteria decision methods. In this context, we point out the technical requirements for such systems and the importance of the data management tool to MCDSS. After a discussion of candidate data models (i.e. relational, hierarchical, and network), we examine the criteria to use in choosing the data model for MCDSS. In the last part of this paper, we review some database management services which support data definition, data manipulation, and data integrity within the multiple-criteria decision making framework. These services guide us when designing the appropriate architecture for the MCDSSâs data component.Information Systems Working Papers Serie

HISTORICAL DATABASES - IT'S ABOUT TIME!

Much recent research in the database community focuses on ways to expand the modelling capabilities of database management systems. The driving force behind this research is the growing size and sophistication of the user community, whose needs and applications seem to always be several steps ahead of the technology. One of the areas where considerable progress has been made in this regard is in the extension of existing data models to represent and manage the temporal dimension of data. In this paper we examine how these enhanced modelling capabilities will increase the functionality of the database management systems of tomorrow. We also introduce the notion of Temporal Representation Transparency as the appropriate abstraction mechanism for providing this increased functionality with minimum burden to the user.Information Systems Working Papers Serie

An Algebraic Approach to XQuery Optimization

As more data is stored in XML and more applications need to process this data, XML query optimization becomes performance critical. While optimization techniques for relational databases have been developed over the last thirty years, the optimization of XML queries poses new challenges. Query optimizers for XQuery, the standard query language for XML data, need to consider both document order and sequence order. Nevertheless, algebraic optimization proved powerful in query optimizers in relational and object oriented databases. Thus, this dissertation presents an algebraic approach to XQuery optimization. In this thesis, an algebra over sequences is presented that allows for a simple translation of XQuery into this algebra. The formal definitions of the operators in this algebra allow us to reason formally about algebraic optimizations. This thesis leverages the power of this formalism when unnesting nested XQuery expressions. In almost all cases unnesting nested queries in XQuery reduces query execution times from hours to seconds or milliseconds. Moreover, this dissertation presents three basic algebraic patterns of nested queries. For every basic pattern a decision tree is developed to select the most effective unnesting equivalence for a given query. Query unnesting extends the search space that can be considered during cost-based optimization of XQuery. As a result, substantially more efficient query execution plans may be detected. This thesis presents two more important cases where the number of plan alternatives leads to substantially shorter query execution times: join ordering and reordering location steps in path expressions. Our algebraic framework detects cases where document order or sequence order is destroyed. However, state-of-the-art techniques for order optimization in cost-based query optimizers have efficient mechanisms to repair order in these cases. The results obtained for query unnesting and cost-based optimization of XQuery underline the need for an algebraic approach to XQuery optimization for efficient XML query processing. Moreover, they are applicable to optimization in relational databases where order semantics are considered

Disjunctively incomplete information in relational databases: modeling and related issues

In this dissertation, the issues related to the information incompleteness in relational databases are explored. In general, this dissertation can be divided into two parts. The first part extends the relational natural join operator and the update operations of insertion and deletion to I-tables, an extended relational model representing inclusively indefinite and maybe information, in a semantically correct manner. Rudimentary or naive algorithms for computing natural joins on I-tables require an exponential number of pair-up operations and block accesses proportional to the size of I-tables due to the combinatorial nature of natural joins on I-tables. Thus, the problem becomes intractable for large I-tables. An algorithm for computing natural joins under the extended model which reduces the number of pair-up operations to a linear order of complexity in general and in the worst case to a polynomial order of complexity with respect to the size of I-tables is proposed in this dissertation. In addition, this algorithm also reduces the number of block accesses to a linear order of complexity with respect to the size of I-tables;The second part is related to the modeling aspect of incomplete databases. An extended relational model, called E-table, is proposed. E-table is capable of representing exclusively disjunctive information. That is, disjunctions of the form P[subscript]1\mid P[subscript]2\mid·s\mid P[subscript]n, where ǁ denotes a generalized logical exclusive or indicating that exactly one of the P[subscript]i\u27s can be true. The information content of an E-table is precisely defined and relational operators of selection, projection, difference, union, intersection, and cartisian product are extended to E-tables in a semantically correct manner. Conditions under which redundancies could arise due to the presence of exclusively disjunctive information are characterized and the procedure for resolving redundancies is presented;Finally, this dissertation is concluded with discussions on the directions for further research in the area of incomplete information modeling. In particular, a sketch of a relational model, IE-table (Inclusive and Exclusive table), for representing both inclusively and exclusively disjunctive information is provided

An approach to modeling database activity

Results in the field of data modeling currently suffer from many of the same ills which plagued data management systems in the late 1960's. Advanced semantic modeling systems such as the Semantic Data Model and the Relational Model/Tasmania are extremely complex to understand as well as somewhat ad hoc in design. Such systems capture only static snapshots of activity in the world being modeled. On the other hand, behavioral models which do attempt to model system dynamics typically provide less overall modeling power than comprehensive semantic models. Further, the specifications of behavior which can be expressed with such models are themselves static snapshots which are not integrated with other database objects.This work describes one approach for capturing dynamic relationships by distilling the concepts found in semantic and behavioral data models into a small number of flexible constructs. The resulting Prototype Activity Modeling System (PAMS) captures the containment, feedback, operational, and state dependency roles of entities in the world being modeled. Further, these definitions of database activity are captured as database objects (rather than as a schema) so as to allow dynamic manipulation of entity roles.The key concept of the approach is the bundle - a purposefully designed extension of time-proven relational database modeling concepts which includes support for presentation ordering and complex Cartesian aggregations. By applying the basic nested bundle principle, it is possible to obtain complex hierarchies of static structural information. The static templates so constructed, when used with a non-procedural query language and the value nomination principle which reduces relations to scalar values when necessary, provide a conventional database modeling system for applications. By extending these templates with the non-procedural thunk principle which embeds query specifications within object definitions, variations caused by dependencies within the application can cause the apparent contents of the database description to change. When further extended by the activity monitoring principle which records the interaction between the application and its environment, these dynamic templates can account for changes outside the scope of the application

Economic data bank management in a developing nation

This dissertation describes the results of a research project which was undertaken at Loughborough University of Technology. The basic objectives of the research project were: (1) to investigate the management elements required for organising the development of an Economic Data Bank (EDB), with particular emphasis on the requirements of a developing nation; (2) to investigate the sociological, political and technical implications associated with organising the development of an EDB in a developing nation. A theoretical framework was established for this study. This was dene after an extensive search and review of literature was performed in the areas of data and data base management systems, management information systems, and computer technology in general. [Continues.

Axiomatic Specification of Database Domain Statics

In the past ten years, much work has been done to add more structure to database models 1 than what is represented by a mere collection of flat relations (Albano & Cardelli [1985], Albano et al. [1986], Borgida eta. [1984], Brodie [1984], Brodie & Ridjanovic [1984], Brodie & Silva (1982], Codd (1979], Hammer & McLeod (1981], King (1984], King & McLeod [1984], [1985], Mylopoulos et al. [1980], Smith & Smith 1977a & b). 2 The informal approach which most of these studies advocate has a number of disadvantages. First, a recent survey of some of the pro­ posed models by Urban & Delcambre [1986] reveals a wide divergence in terminology and con­ cepts, making comparison of the expressive power of these models difficult. Second, undefined or even ill-defined concepts are a hindrance, not an aid, for the analysis of the Universe of Discourse (UoD). Third, informal treatment 9f such complex structures as set hierarchies, gen­ eralization hierarchies and aggregation hierarchies all in one model, with some dynamics thrown in for good measure, bodes ill for the consistency of these theories. The first goal of the research reported on is to integrate the static structures which these models propose in one coherent, axiomatic framework. It will be shown in chapter 7 that the theory presented here provides the needed conceptual foundations for these models. A second aim is to provide a possible worlds framework onto which to graft theories of the dynamics of the UoD. The third aim is to provide clear concepts which can aid the database model designer in his or her thinking about the UoD. In this report we concentrate on the first goal only, leav­ ing the formulation of theories of domain dynamics and the application to system development as research goals for the near future

Multi-Schema-Version Data Management

Modern agile software development methods allow to continuously evolve software systems by easily adding new features, fixing bugs, and adapting the software to changing requirements and conditions while it is continuously used by the users. A major obstacle in the agile evolution is the underlying database that persists the software system’s data from day one on. Hence, evolving the database schema requires to evolve the existing data accordingly—at this point, the currently established solutions are very expensive and error-prone and far from agile. In this thesis, we present InVerDa, a multi-schema-version database system to facilitate agile database development. Multi-schema-version database systems provide multiple schema versions within the same database, where each schema version itself behaves like a regular single-schema database. Creating new schema versions is very simple to provide the desired agility for database development. All created schema versions can co-exist and write operations are immediately propagated between schema versions with a best-effort strategy. Developers do not have to implement the propagation logic of data accesses between schema versions by hand, but InVerDa automatically generates it. To facilitate multi-schema-version database systems, we equip developers with a relational complete and bidirectional database evolution language (BiDEL) that allows to easily evolve existing schema versions to new ones. BiDEL allows to express the evolution of both the schema and the data both forwards and backwards in intuitive and consistent operations; the BiDEL evolution scripts are orders of magnitude shorter than implementing the same behavior with standard SQL and are even less likely to be erroneous, since they describe a developer’s intention of the evolution exclusively on the level of tables without further technical details. Having the developers’ intentions explicitly given in the BiDEL scripts further allows to create a new schema version by merging already existing ones. Having multiple co-existing schema versions in one database raises the need for a sophisticated physical materialization. Multi-schema-version database systems provide full data independence, hence the database administrator can choose a feasible materialization, whereby the multi-schema-version database system internally ensures that no data is lost. The search space of possible materializations can grow exponentially with the number of schema versions. Therefore, we present an adviser that releases the database administrator from diving into the complex performance characteristics of multi-schema-version database systems and merely proposes an optimized materialization for a given workload within seconds. Optimized materializations have shown to improve the performance for a given workload by orders of magnitude. We formally guarantee data independence for multi-schema-version database systems. To this end, we show that every single schema version behaves like a regular single-schema database independent of the chosen physical materialization. This important guarantee allows to easily evolve and access the database in agile software development—all the important features of relational databases, such as transaction guarantees, are preserved. To the best of our knowledge, we are the first to realize such a multi-schema-version database system that allows agile evolution of production databases with full support of co-existing schema versions and formally guaranteed data independence