Managing Schema Change in an Heterogeneous Environment

Change is inevitable even for persistent information. Effectively managing change of persistent information, which includes the specification, execution and the maintenance of any derived information, is critical and must be addressed by all database systems. Today, for every data model there exists a well-defined set of change primitives that can alter both the structure (the schema) and the data. Several proposals also exist for incrementally propagating a primitive change to any derived information (or view). However, existing support is lacking in two ways. First, change primitives as presented in literature are very limiting in terms of their capabilities allowing users to simply add or remove schema elements. More complex types of changes such the merging or splitting of schema elements are not supported in a principled manner. Second, algorithms for maintaining derived information often do not account for the potential heterogeneity between the source and the target. The goal of this dissertation is to provide solutions that address these two key issues. The first part of this dissertation addresses the challenge of expressing a rich complex set of changes. We propose the SERF (Schema Evolution through an Extensible, Re-usable and Flexible) framework that allows users to perform a wide range of complex user-defined schema transformations. Our approach combines existing schema evolution primitives using OQL (object query language) as the glue logic. Within the context of this work, we look at the different domains in which SERF can be applied, including web site management. To further enrich our framework, we also investigate the optimization and verification of SERF transformations. The second part of this dissertation addresses the problem of maintaining views in the face of source changes when the source and the view are not in the same data model. With today\u27s increasing heterogeneity in information structure, it is critical that maintenance of views addresses the data model boundaries. However, view definitions that go across data models are limited to hard-coded algorithms, thereby making it difficult to develop general maintenance algorithms. We provide a two-step solution for this problem. We have developed a cross algebra, that defines views such that there is no restriction that forces the view and the source data models to be the same. We then define update propagation algorithms that can propagate changes from source to target irrespective of the exact translation and the data models. We validate our ideas by applying them to translation and change propagation between the XML and relational data models

An object query language for multimedia federations

The Fischlar system provides a large centralised repository of multimedia files. As expansion is difficult in centralised systems and as different user groups have a requirement to define their own schemas, the EGTV (Efficient Global Transactions for Video) project was established to examine how the distribution of this database could be managed. The federated database approach is advocated where global schema is designed in a top-down approach, while all multimedia and textual data is stored in object-oriented (O-O) and object-relational (0-R) compliant databases. This thesis investigates queries and updates on large multimedia collections organised in the database federation. The goal of this research is to provide a generic query language capable of interrogating global and local multimedia database schemas. Therefore, a new query language EQL is defined to facilitate the querying of object-oriented and objectrelational database schemas in a database and platform independent manner, and acts as a canonical language for database federations. A new canonical language was required as the existing query language standards (SQL: 1999 and OQL) axe generally incompatible and translation between them is not trivial. EQL is supported with a formally defined object algebra and specified semantics for query evaluation. The ability to capture and store metadata of multiple database schemas is essential when constructing and querying a federated schema. Therefore we also present a new platform independent metamodel for specifying multimedia schemas stored in both object-oriented and object-relational databases. This metadata information is later used for the construction of a global schemas, and during the evaluation of local and global queries. Another important feature of any federated system is the ability to unambiguously define database schemas. The schema definition language for an EGTV database federation must be capable of specifying both object-oriented and object-relational schemas in the database independent format. As XML represents a standard for encoding and distributing data across various platforms, a language based upon XML has been developed as a part of our research. The ODLx (Object Definition Language XML) language specifies a set of XMLbased structures for defining complex database schemas capable of representing different multimedia types. The language is fully integrated with the EGTV metamodel through which ODLx schemas can be mapped to 0-0 and 0-R databases

Extending information retrieval system model to improve interactive web searching.

The research set out with the broad objective of developing new tools to support Web information searching. A survey showed that a substantial number of interactive search tools were being developed but little work on how these new developments fitted into the general aim of helping people find information. Due to this it proved difficult to compare and analyse how tools help and affect users and where they belong in a general scheme of information search tools. A key reason for a lack of better information searching tools was identified in the ill-suited nature of existing information retrieval system models. The traditional information retrieval model is extended by synthesising work in information retrieval and information seeking research. The purpose of this new holistic search model is to assist information system practitioners in identifying, hypothesising, designing and evaluating Web information searching tools. Using the model, a term relevance feedback tool called ‘Tag and Keyword’ (TKy) was developed in a Web browser and it was hypothesised that it could improve query reformulation and reduce unnecessary browsing. The tool was laboratory experimented and quantitative analysis showed statistical significances in increased query reformulations and in reduced Web browsing (per query). Subjects were interviewed after the experiment and qualitative analysis revealed that they found the tool useful and saved time. Interestingly, exploratory analysis on collected data identified three different methods in which subjects had utilised the TKy tool. The research developed a holistic search model for Web searching and demonstrated that it can be used to hypothesise, design and evaluate information searching tools. Information system practitioners using it can better understand the context in which their search tools are developed and how these relate to users’ search processes and other search tools

The exploration of a category theory-based virtual Geometrical product specification system for design and manufacturing

In order to ensure quality of products and to facilitate global outsourcing, almost all the so-called “world-class” manufacturing companies nowadays are applying various tools and methods to maintain the consistency of a product’s characteristics throughout its manufacturing life cycle. Among these, for ensuring the consistency of the geometric characteristics, a tolerancing language − the Geometrical Product Specification (GPS) has been widely adopted to precisely transform the functional requirements from customers into manufactured workpieces expressed as tolerance notes in technical drawings. Although commonly acknowledged by industrial users as one of the most successful efforts in integrating existing manufacturing life-cycle standards, current GPS implementations and software packages suffer from several drawbacks in their practical use, possibly the most significant, the difficulties in inferring the data for the “best” solutions. The problem stemmed from the foundation of data structures and knowledge-based system design. This indicates that there need to be a “new” software system to facilitate GPS applications. The presented thesis introduced an innovative knowledge-based system − the VirtualGPS − that provides an integrated GPS knowledge platform based on a stable and efficient database structure with knowledge generation and accessing facilities. The system focuses on solving the intrinsic product design and production problems by acting as a virtual domain expert through translating GPS standards and rules into the forms of computerized expert advices and warnings. Furthermore, this system can be used as a training tool for young and new engineers to understand the huge amount of GPS standards in a relative “quicker” manner. The thesis started with a detailed discussion of the proposed categorical modelling mechanism, which has been devised based on the Category Theory. It provided a unified mechanism for knowledge acquisition and representation, knowledge-based system design, and database schema modelling. As a core part for assessing this knowledge-based system, the implementation of the categorical Database Management System (DBMS) is also presented in this thesis. The focus then moved on to demonstrate the design and implementation of the proposed VirtualGPS system. The tests and evaluations of this system were illustrated in Chapter 6. Finally, the thesis summarized the contributions to knowledge in Chapter 7. After thoroughly reviewing the project, the conclusions reached construe that the III entire VirtualGPS system was designed and implemented to conform to Category Theory and object-oriented programming rules. The initial tests and performance analyses show that the system facilitates the geometric product manufacturing operations and benefits the manufacturers and engineers alike from function designs, to a manufacturing and verification

Native Language OLAP Query Execution

Online Analytical Processing (OLAP) applications are widely used in the components of contemporary Decision Support systems. However, existing OLAP query languages are neither efficient nor intuitive for developers. In particular, Microsoft’s Multidimensional Expressions language (MDX), the de-facto standard for OLAP, is essentially a string-based extension to SQL that hinders code refactoring, limits compile-time checking, and provides no object-oriented functionality whatsoever. In this thesis, we present Native language OLAP query eXecution, or NOX, a framework that provides responsive and intuitive query facilities. To this end, we exploit the underlying OLAP conceptual data model and provide a clean integration between the server and the client language. NOX queries are object-oriented and support inheritance, refactoring and compile-time checking. Underlying this functionality is a domain specific algebra and language grammar that are used to transparently convert client side queries written in the native development language into algebraic operations understood by the server. In our prototype of NOX, JAVA is used as the native language. We provide client side libraries that define an API for programmers to use for writing OLAP queries. We investigate the design of NOX through a series of real world query examples. Specifically, we explore the following: fundamental SELECTION and PROJECTION, set operations, hierarchies, parametrization and query inheritance. We compare NOX queries to MDX and show the intuitiveness and robustness of NOX. We also investigate NOX expressiveness with respect to MDX from an algebraic point of view by demonstrating the correspondence of the two approaches in terms of SELECTION and PROJECTION operations. We believe the practical benefit of NOX-style query processing is significant. In short, it largely reduces OLAP database access to the manipulation of client side, in-memory data object

Searching and ranking in entity-relationship graphs

The Web bears the potential to become the world';s most comprehensive knowledge base. Organizing information from the Web into entity-relationship graph structures could be a first step towards unleashing this potential. In a second step, the inherent semantics of such structures would have to be exploited by expressive search techniques that go beyond today';s keyword search paradigm. In this realm, as a first contribution of this thesis, we present NAGA (Not Another Google Answer), a new semantic search engine. NAGA provides an expressive, graph-based query language that enables queries with entities and relationships. The results are retrieved based on subgraph matching techniques and ranked by means of a statistical ranking model. As a second contribution, we present STAR (Steiner Tree Approximation in Relationship Graphs), an efficient technique for finding "close'; relations (i.e., compact connections) between k(> 2) entities of interest in large entity-relationship graphs. Our third contribution is MING (Mining Informative Graphs). MING is an efficient method for retrieving "informative'; subgraphs for k(> 2) entities of interest from an entity-relationship graph. Intuitively, these would be subgraphs that can explain the relations between the k entities of interest. The knowledge discovery tasks supported by MING have a stronger semantic flavor than the ones supported by STAR. STAR and MING are integrated into the query answering component of the NAGA engine. NAGA itself is a fully implemented prototype system and is part of the YAGONAGA project.Das Web birgt in sich das Potential zur umfangreichsten Wissensbasis der Welt zu werden. Das Organisieren der Information aus dem Web in Entity-Relationship-Graphstrukturen könnte ein erster Schritt sein, um dieses Potential zu entfalten. In einem zweiten Schritt müssten ausdrucksstarke Suchtechniken entwickelt werden, die über das heutige Keyword-basierte Suchparadigma hinausgehen und die inhärente Semantik solcher Strukturen ausnutzen. In diesem Rahmen stellen wir als ersten Beitrag dieser Arbeit NAGA (Not Another Google Answer) vor, eine neue semantische Suchmaschine. NAGA bietet eine ausdrucksstarke, graphbasierte Anfragesprache, die Anfragen mit Entitäten und Relationen ermöglicht. Die Ergebnisse werden durch Subgraph-Matching-Techniken gefunden und mithilfe eines statistischen Modells in eine Rangliste gebracht. Als zweiten Beitrag stellen wir STAR (Steiner Tree Approximation in Relationship Graphs) vor, eine effiziente Technik, um "nahe'; Relationen (d.h. kompakte Verbindungen) zwischen k(> 2) Entitäten in großen Entity-Relationship-Graphen zu finden. Unser dritter Beitrag ist MING (Mining Informative Graphs). MING ist eine effiziente Methode, die das Finden von "informativen'; Subgraphen für k(> 2) Entitäten aus einem Entity-Relationship-Graphen ermöglicht. Dies sind Subgraphen, die die Beziehungen zwischen den k Entitäten erklären können. Im Vergleich zu STAR unterstützt MING Aufgaben der Wissensexploration, die einen stärkeren semantischen Charakter haben. Sowohl STAR als auch MING sind in die Query-Answering-Komponente der NAGA-Suchmaschine integriert. NAGA selbst ist ein vollständig implementiertes Prototypsystem und Teil des YAGO-NAGA-Projekts

An object-oriented database for the compilation of signal transduction pathways

Transpath ist ein Informationssystem fuer Signaltransduktionsnetze. Der Fokus liegt auf Signalpfaden und -kaskaden, die an der Regulation von Transkriptionsfaktoren beteiligt sind. Molekuele und Reaktionenen werden als Knoten in einem Signalgraphen aufgefasst und, zusammen mit Informationen ueber ihre Lokalisation, Qualitaet, Familienhierarchien und Signalmotive, in einer objekt-orientierten Databank gespeichert. Weiterhin werden Verweise zu anderen Datenbanken und der Originalliteratur gespeichert. Transpath unterscheidet zwischen den Zuständen eines Signalmoleküles und kann die Reaktionsmechanismen der Signalinteraktionen angemessen beschreiben. Transpath is über das World Wide Web (http://transpath.gbf.de) verfügbar durch ein Servlet-basiertes Interface, das dynamische Sichten direkt aus dem Inhalt der Datenbank erzeugt. Signalpfad-Abfragen und verschiedene Arten der Visualisierung werden zusammen mit textbasierenden Abfragen und Detailinformationen zu einzelnen Eintraegen unterstuetzt. Es wird gezeigt dass die Datenbank zur Analyse des Signalnetzes von Nutzen ist und die Grundlage fuer Simulationen liefern kann.Transpath is an information system on signal-transduction networks. It focuses on pathways involved in the regulation of transcription factors. Molecules and reactions are the nodes in a signaling graph. They are stored in an object-oriented database, together with information about their location, quality, family relationships and signaling motifs. Also stored are links to other databases and references to the original literature. Transpath differentiates between the states of a signal molecule, and can adequately describe the reaction mechanisms of signaling interactions. It is available over the web (http://transpath.gbf.de) through a Servlet-based interface, that creates dynamic content directly from the contents of the database. Pathway query mechanisms and several kinds of display are provided for the database in addition to text-based queries and information on single entries. We show that the database is useful for analysis of the signaling network and can provide the basis for simulations