Query processing in temporal object-oriented databases

This PhD thesis is concerned with historical data management in the context of objectoriented databases. An extensible approach has been explored to processing temporal object queries within a uniform query framework. By the uniform framework, we mean temporal queries can be processed within the existing object-oriented framework that is extended from relational framework, by extending the existing query processing techniques and strategies developed for OODBs and RDBs. The unified model of OODBs and RDBs in UmSQL/X has been adopted as a basis for this purpose. A temporal object data model is thereby defined by incorporating a time dimension into this unified model of OODBs and RDBs to form temporal relational-like cubes but with the addition of aggregation and inheritance hierarchies. A query algebra, that accesses objects through these associations of aggregation, inheritance and timereference, is then defined as a general query model /language. Due to the extensive features of our data model and reducibility of the algebra, a layered structure of query processor is presented that provides a uniforrn framework for processing temporal object queries. Within the uniform framework, query transformation is carried out based on a set of transformation rules identified that includes the known relational and object rules plus those pertaining to the time dimension. To evaluate a temporal query involving a path with timereference, a strategy of decomposition is proposed. That is, evaluation of an enhanced path, which is defined to extend a path with time-reference, is decomposed by initially dividing the path into two sub-paths: one containing the time-stamped class that can be optimized by making use of the ordering information of temporal data and another an ordinary sub-path (without time-stamped classes) which can be further decomposed and evaluated using different algorithms. The intermediate results of traversing the two sub-paths are then joined together to create the query output. Algorithms for processing the decomposed query components, i. e., time-related operation algorithms, four join algorithms (nested-loop forward join, sort-merge forward join, nested-loop reverse join and sort-merge reverse join) and their modifications, have been presented with cost analysis and implemented with stream processing techniques using C++. Simulation results are also provided. Both cost analysis and simulation show the effects of time on the query processing algorithms: the join time cost is linearly increased with the expansion in the number of time-epochs (time-dimension in the case of a regular TS). It is also shown that using heuristics that make use of time information can lead to a significant time cost saving. Query processing with incomplete temporal data has also been discussed

Algorithms for generation of path-methods in object-oriented databases

A path-method is a mechanism in object-oriented databases (OODBs) to retrieve or to update information relevant to one class that is not stored with that class but with some other class. A path-method is a method which traverses from one class through a chain of connections between classes to access information at another class. However, it is a difficult task for a user to write path-methods, because it might require comprehensive knowledge of many classes of the conceptual schema, while a typical user has often incomplete or even inconsistent knowledge of the schema. This dissertation proposes an approach to the generation of path-methods in an OODB to solve this problem. We have developed the Path-Method Generator (P MG) system, which generates path-methods according to a naive user\u27s requests. PMG is based on access weights which reflect the relative frequency of the connections and precomputed access relevance between every pair of classes of the OODB computed from access weights of the connections. We present specific rules for access weight assignment, efficient algorithms to compute access relevance in a single OODB, and a variety of traversal algorithms based on access weights and precomputed access relevance. Experiments with a university environment OODB and a sample of path-methods identify some of these algorithms as very successful in generating most of the desired path-methods. Thus, the PMG system is an efficient tool for aiding the user with the difficult task of querying and updating a large OODB. The path-method generation in an interoperable multi object-oriented database (IM-OODB) is even more difficult than for a single OODB, since a user has to be familiar with several OODBs. We use a hierarchical approach for deriving efficient online algorithms for the computation of access relevance in an IM-OODB, based on precomputed access relevance for each autonomous OODB. In an IM-OODB the access relevance is used as guide in generating path-methods between the classes of different OODBs

Abstraction of an object-oriented vocabulary by providing a standardized interface

Controlled vocabularies are ubiquitous in varied application fields. They are particularly helpful in the medical field since they can unify disparate terminologies and provide information in a compact, comprehensible manner. In this thesis, we present a mechanism to efficiently retrieve and update knowledge stored in a controlled vocabulary modeled as an Object-Oriented Database (OODB) system. We aim to provide a standardized interface to the vocabulary, such that the implementation details of the vocabulary are transparent to all users. The user of this standardized interface will typically be an application programmer who is trying to provide the vocabulary\u27s knowledge-base to end users. We first describe our approach to creating the standardized interface. We then present the software architecture and design for it. We conclude by describing the implementation of this standardized interface

Interactive and batch creation of OODB medical vocabularies

Controlled vocabularies are becoming popular for knowledge representation and querying. They are particularly helpful in the medical field since they can unify disparate terminologies and provide information in a compact, comprehensible manner. In this thesis, we present a mechanism to create OODB controlled medical vocabularies from flat-file format. We also describe a tool by which a user can interactively create, edit and browse the vocabulary. For better understanding of the structure of the vocabulary we designed our interface as a graphical editor and browser. The user of this interface will typically be a medical expert who either wants to add new concepts to the vocabulary or create a new vocabulary from scratch. We first describe our approach for creating the vocabulary from an existing flat-file format by batch processing. We then present the software architecture and design of an interactive vocabulary creator (IVC)

Implementation of an object-oriented university database using VODAK/VML prototype-2/C++

Object-oriented database (OODB) technology has become very popular and successful in recent years. Currently, there are many commercial object-oriented database systems available that are used for developing large and complex real world applications. In addition, there are many research prototypes of object-oriented databases available. In a joint research project of the CIS Dept at NJIT and GMD-IPSI an object-oriented data model called the Dual Model was developed. Using this Dual Model a university environment database schema was designed. This univesity database schema was implemented using the VODAK/VML OODB prototype - 1. The university database was then reimplemented using the C++ programming language, without any underlying database. In this thesis we have implemented a Dual Model based version of the university database, using the VODAK/VML OODB prototype - 2. This prototype is the first implemented prototype, which separates the structural and semantic aspects of a class definition. It also uses C++ as implementation language, while the previous prototype was based on Smalltalk - 80. To interact with the database we have developed a university database browser using the X11/MOTIF toolkit and C++

The advantages and cost effectiveness of database improvement methods

Relational databases have proved inadequate for supporting new classes of applications, and as a consequence, a number of new approaches have been taken (Blaha 1998), (Harrington 2000). The most salient alternatives are denormalisation and conversion to an object-oriented database (Douglas 1997). Denormalisation can provide better performance but has deficiencies with respect to data modelling. Object-oriented databases can provide increased performance efficiency but without the deficiencies in data modelling (Blaha 2000). Although there have been various benchmark tests reported, none of these tests have compared normalised, object oriented and de-normalised databases. This research shows that a non-normalised database for data containing type code complexity would be normalised in the process of conversion to an objectoriented database. This helps to correct badly organised data and so gives the performance benefits of de-normalisation while improving data modelling. The costs of conversion from relational databases to object oriented databases were also examined. Costs were based on published benchmark tests, a benchmark carried out during this study and case studies. The benchmark tests were based on an engineering database benchmark. Engineering problems such as computer-aided design and manufacturing have much to gain from conversion to object-oriented databases. Costs were calculated for coding and development, and also for operation. It was found that conversion to an object-oriented database was not usually cost effective as many of the performance benefits could be achieved by the far cheaper process of de-normalisation, or by using the performance improving facilities provided by many relational database systems such as indexing or partitioning or by simply upgrading the system hardware. It is concluded therefore that while object oriented databases are a better alternative for databases built from scratch, the conversion of a legacy relational database to an object oriented database is not necessarily cost effective

Developing techniques for enhancing comprehensibility of controlled medical terminologies

A controlled medical terminology (CMT) is a collection of concepts (or terms) that are used in the medical domain. Typically, a CMT also contains attributes of those concepts and/or relationships between those concepts. Electronic CMTs are extremely useful and important for communication between and integration of independent information systems in healthcare, because data in this area is highly fragmented. A single query in this area might involve several databases, e.g., a clinical database, a pharmacy database, a radiology database, and a lab test database. Unfortunately, the extensive sizes of CMTs, often containing tens of thousands of concepts and hundreds of thousands of relationships between pairs of those concepts, impose steep learning curves for new users of such CMTs. In this dissertation, we address the problem of helping a user to orient himself in an existing large CMT. In order to help a user comprehend a large, complex CMT, we need to provide abstract views of the CMT. However, at this time, no tools exist for providing a user with such abstract views. One reason for the lack of tools is the absence of a good theory on how to partition an overwhelming CMT into manageable pieces. In this dissertation, we try to overcome the described problem by using a threepronged approach. (1) We use the power of Object-Oriented Databases to design a schema extraction process for large, complex CMTs. The schema resulting from this process provides an excellent, compact representation of the CMT. (2) We develop a theory and a methodology for partitioning a large OODI3 schema, modeled as a graph, into small meaningful units. The methodology relies on the interaction between a human and a computer, making optimal use of the human\u27s semantic knowledge and the computer\u27s speed. Furthermore, the theory and methodology developed for the scbemalevel partitioning are also adapted to the object-level of a CMT. (3) We use purely structural similarities for partitioning CMTs, eliminating the need for a human expert in the partitioning methodology mentioned above. Two large medical terminologies are used as our test beds, the Medical Entities Dictionary (MED) and the Unified Medical Language System (UMLS), which itself contains a number of terminologies

A Smalltalk-based extension to traditional Geographic Information Systems

The Dynamic Environmental Effects Model{copyright} (DEEM), under development at Argonne National Laboratory, is a fully object-based modeling software system that supports distributed, dynamic representation of the interlinked processes and behavior of the earth`s surface and near-surface environment, at variable scales of resolution and aggregation. Many of these real world objects are not stored in a format conducive to efficient GIS usage. Their dynamic nature, complexity and number of possible DEEM entity classes precluded efficient integration with traditional GIS technologies due to the loosely coupled nature of their data representations. To address these shortcomings, an intelligent object-oriented GIS engine (OOGIS) was developed. This engine provides not only a spatially optimized object representation, but also direct linkages to the underlying object, its data and behaviors