Heterogeneous Database Systems Research Articles

Progress in database search strategies

Retrieval speed and precision ultimately determine the success of any database system. This article outlines the challenges posed by distributed and heterogeneous database systems, including those that store unstructured data, and surveys recent work. Much work remains to help users retrieve information with ease and efficiency from a heterogeneous environment in which relational, object-oriented, textual, and pictorial databases coexist. The article outlines the progress that has been made in query processing in distributed relational database systems and heterogeneous and multidatabase systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Commit protocols for externalized-commit heterogeneous database systems

In designing a heterogeneous database systems, one of the main technical challenges is developing techniques for ensuring global commit. That is, guaranteeing that a transaction spanning multiple individual database management systems (DBMSs) either commits at all the participating DBMSs or at none of them. Previous work in this area typically assumes that the participating DBMSs do not provide a mechanism for interacting with their commit facilities. While this is true in many cases, in practice there are systems which support a programmatic interface to their commit protocols. We refer to database systems offering such facilities asexternalized commit DBMSs.

The Jupiter system: an environment for multidatabase interoperability

The goal of the Jupiter system is to provide interoperability services to a federation of autonomous and possibly heterogeneous database systems. Interoperability is the ability to connect software systems in a manner which facilitates transparent access to enterprise data resources, which may be distributed among legacy applications across multiple heterogeneous software and hardware platforms. The participants are free to withdraw at any time, with the result that global integration of the participant schemas is not seen as a feasible solution. Our solution is to provide a multidatabase layer and a suitable interoperator language to allow information providers to construct loosely-coupled interoperable autonomous information systems. The enor mous problems faced by information system providers are compounded by the difficulty of integrating key applications which have been developed using traditional methods with applications developed using, for example, object- oriented technology. A goal of our research is to address the area of multidatabase interoperability and, to this end, we have constructed the Jupiter prototype.

Answering heterogeneous database queries with degrees of uncertainty

In heterogeneous database systems,partial values have been used to resolve some schema integration problems. Performing operations on partial values may producemaybe tuples in the query result which cannot be compared. Thus, users have no way to distinguish which maybe tuple is the most possible answer. In this paper, the concept of partial values is generalized toprobabilistic partial values. We propose an approach to resolve the schema integration problems using probabilistic partial values and develop a full set of extended relational operators for manipulating relations containing probabilistic partial values. With this approach, the uncertain answer tuples of a query are associated with degrees of uncertainty (represented by probabilities). That provides users a comparison among maybe tuples and a better understanding on the query results. Besides, extended selection and join are generalized to α-selection and α-join, respectively, which can be used to filter out maybe tuples with low probabilities — those which have probabilities smaller than α.

The INtersect concept for multidatabase system integration in the pharmaceutical industry

The industry trends facing information systems in the 1990's involve a matrix of complex requirements. The migration from centralized mainframe computing to desktop personal computing has created opportunities and challenges in moving access to and control of information closer to the end-user. Within this new wave of computing, there has been a drive to move the access control for information to the desktop of the user. Although, graphical user standards were introduced in order to ease of use and provide a consistent look and feel to desktop applications. This provided some assistance in shielding the complexity of the various systems, however it did not address the difficulties presented in accessing heterogeneous database systems on various platforms.

Engineering data management: achieving integration through database technology

An architecture is given for engineering data management that incorporates current work on engineering product standards as well as current work in database research. In particular, a framework that views an engineering design environment as an integrated, heterogeneous database system is presented. This integrated view of data makes use of data exchange standards in PDES/STEP, presenting a framework for the representation of meta data that describes an object-oriented view of data and supports an object-oriented query language for the retrieval of data from multiple data sources. How the use of active database technology supports a rule-based approach to constraint propagation and change notification is also described. >

On Intelligent Database Systems

In response to the limitations of comtemporary database management systems in addressing the requirements of many potential application environments, and in view of the characteristics of emerging interconnected systems, we examine research directions involving adding more 'intelligence' to database systems. Three major thrusts in the intelligent database systems area are discussed. The first involves increasing the modeling power to represent an application environment. The second emphasis centers on enhancing the functionality of such a system to include rule-based inference capabilities. The third direction focuses on supporting the interoperability of multiple, autonomous, heterogeneous database systems. We provide here a view of the first two thrusts, and examine the third via a description of the Remote-Exchange research effort currently underway at USC.

Federated databases and systems: Part II ? A tutorial on their resource consolidation

The issues and solutions for the interoperability of a class of heterogeneous databases and their database systems are expounded in two parts. Part I presented the data-sharing issues in federated databases and systems (Hsiao, 1992). The present article explores resource-consolidation issues. Interoperability in this context refers to data sharing among heterogeneous databases, and to resource consolidation of computer hardware, system software, and support personnel. Resource consolidation requires the presence of a database system architecture which supports the heterogeneous system software, thereby eliminating the need for various computer hardware and support personnel. The class of heterogeneous databases and database systems expounded herein is termed federated, meaning that they are joined in order to meet certain organizational requirements and because they require their respective application specificities, integrity constraints, and security requirements to be upheld. Federated databases and systems are new. While there are no technological solutions, there has been considerable research towards their development. This tutorial is aimed at exposing the need for such solutions. A taxonomy is introduced in our review of existing research undertakings and exploratory developments. With this taxonomy, we contrast and compare various approaches to federating databases and systems.

Federated databases and systems: Part I?A tutorial on their data sharing

The issues and solutions for the interoperability of a class of heterogeneous databases and their database systems are expounded in two parts. Part I presents the data-sharing issues in federated databases and systems. Part II, which will appear in a future issue, explores resource-consolidation issues. Interoperability in this context refers to data sharing among heterogeneous databases, and to resource consolidation of computer hardware, system software, and support personnel. Resource consolidation requires the presence of a database system architecture which supports the heterogeneous system software, thereby eliminating the need for various computer hardware and support personnel. The class of heterogeneous databases and database systems expounded herein is termed federated, meaning that they are joined in order to meet certain organizational requirements and because they require their respective application specificities, integrity constraints, and security requirements to be upheld. Federated databases and systems are new. While there are no technological solutions, there has been considerable research towards their development. This tutorial is aimed at exposing the need for such solutions. A taxonomy is introduced in our review of existing research undertakings and exploratory developments. With this taxonomy, we contrast and compare various approaches to federating databases and systems.

E-R Approach to Distributed Heterogeneous Database Systems for Integrated Manufacturing

A critical step towards computer integrated manufacturing (CIM) is the integration of computer-aided design (CAD) and computer-aided manufacturing (CAM). Well developed CAD, CAM, and Business data processing systems generally exist in an organization. These systems represent years of work and very large investment for the organization. Thus a necessary condition for integration is defining schemes through which existing engineering and non-engineering data can be represented and manipulated in an integrated way. In this paper a Common Data Model (CDM) approach to distributed heterogeneous database is adopted for CAD/CAM integration and an Extended-Entity- Category-Relationship (EECS) Model (an extension of ER model) is proposed. The use of EECR model as a common conceptual data model for representing engineering and non-engineering data is discussed.

Object-oriented databases for new applications

As applications have grown more sophisticated, they have placed greater demands on underlying database technology. In this paper we examine some of the shortcomings of conventional database technologies in the face of these demands, and then discuss how emerging object-oriented database technology addresses these shortcomings in several specific application areas: user interface applications, multimedia databases, CAD databases, statistical and scientific databases, and management of heterogeneous database systems. We conclude with a list of remaining challenges and some suggestions for further research.

Update synchronization pursuing site autonomy in heterogeneous distributed databases

Although many researches in distributed database area perceive that the only practical way to construct a distributed database system from already existing local heterogeneous database systems is to integrate them by guaranteeing local site autonomy, an efficient update synchronization scheme for the system has not been developed so far. Furthermore, most previous concurrency control schemes for heterogeneous systems failed to guarantee site autonomy or global serializability. In this paper, we propose a concurrency control scheme that guarantees both global serializability of concurrent transaction execution and site autonomy for heterogeneous distributed database systems.

Classifying schematic and data heterogeneity in multidatabase systems

A complete framework for enumerating and classifying the types of multidatabase system (MDBS) structural and representational discrepancies is developed. The framework is structured according to a relational database schema and is both practical and complete. It was used to build the UniSQL/M commercial multidatabase system. This MDBS was built over Structured-Query-Language-based relational database systems and a unified relational and object-oriented database system named UniSQL/X. However, the results are substantially applicable to heterogeneous database systems that use a nonrelational data model (for example, an object-oriented data model) as the common data model and allow the formulation of queries directly against the component database schemas. >

Distributed management of transactions in heterogeneous distributed database systems

In the two phase commit protocol, the coordinator decides to commit the distributed transaction if all its subtransactions are in a state called the “prepared state”. We have increased the semantics of the two phase commit protocols by replacing the prepared state by more restrictive states called the “source state” and the “serializable state”. The source state ensures that the execution of committed distributed transactions is not only atomic but also serializable. It also ensures that distributed transactions cannot interfere with other distributed transactions through local transactions, but it does not ensure a serializable view of the distributed database if local transactions are taken into account. The serializable state ensures that the execution is serializable also if local transactions are taken into account. Which of the two correctness criteria is appropriate for global concurrency control depends on the distributed applications of the system. In the proposed mechanism, each interconnected site supports the source state or the serializable state. Various methods of supporting these states are presented. Which method is appropriate for a site depends on the concurrency control method and the autonomy requirements of the site.

A non-two-phase locking protocol for global concurrency control in distributed heterogeneous database systems

A concurrency control method is proposed for global transactions in a distributed heterogeneous database system. This method is applicable when the database sites are interconnected in a rooted tree fashion. It guarantees deadlock freedom in addition to serializability. A general architecture of a heterogeneous system is given. The global transaction manager (GTM) decomposes the global transactions initiated at a site and the subtransactions received from other sites into smaller subtransactions, some of which are sent to the GTMs of the other sites, and those remaining, called g-local transactions, are to be executed by the local transaction manager (LTM) at that site. A concurrency control mechanism ensures serializability among: the local transactions (including the g-local transactions of the global ones) at each site, the global transactions and the global and local transactions together.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Architecture for distributed multimedia database systems

In the past few years considerable demand for useroriented multimedia information systems has developed. These systems must provide a rich set of functionality so that new, complex, and interesting applications can be addressed. This places considerable importance on the management of diverse data types including text, omages, audio and video; these requirements in turn generate the need for a new generation of distributed heterogeneous multimedia database systems. In this paper, a set of f functional requirements is identified for a multimedia server considering database management, object synchronization and integration, and multimedia query processing. A generalization of the requirements to a distributed system is presented, and some current research and developing activities are discussed.

E-R Approach to Distributed Heterogeneous Database Systems for Integrated Manufacturing

A critical step towards computer integrated manufacturing CIM is the integration of computer-aided design CAD and computer-aided manufacturing CAM. Well developed CAD, CAM, and Business data processing systems generally exist in an organization. These systems represent years of work and a very large investment for the organization. Thus a necessary condition for integration is defining schemes through which existing engineering and non-engineering data can be represented and manipulated in an integrated way. In this paper a Common Data Model CDM approach to distributed heterogeneous database is adopted for CAD/CAM integration and an Extended-Entity-Category-Relationship EECS Model an extension of ER model is proposed. The use of EECR model as a common conceptual data model for representing engineering and non-engineering data is discussed.

The SIRIUS-DELTA architecture: A framework for co-operating database systems

SIRIUS-DELTA is a distributed database system which is aimed at co-operation of heterogeneous local database systems. It illustrates how the Open Systems approach has been used in the context of distributed database systems, mainly in its architecture and its Data Manipulation Protocol. It also illustrates that distributed databases is an area where co-operation between ISO/TC97/SC5 Programming Languages and ISO/TC97/SC16 Open Systems Interconnection sub-committees is of a major importance for future developments.

Heterogeneous databases and high level abstraction

A heterogeneous database management system combines multiple dissimilar models of data within a single integrated system. The objective is to allow a user to access data independently of how it is actually organized. For example, a user may access a database as though it were stored relationally (i.e., in tables) [CODD70], even though it is actually stored as a CODASYL/DBTG or network database [CODA71]. In addition, different subpieces of the database may be organized under different data models. The heterogeneous database system must present these to the user as an integrated whole. The user's model of his data may be different from any of the models chosen to implement it. Rather than construct a new database system from scratch, we are interested in constructing a heterogeneous system out of existing systems. The key difficulties with this approach are: (1) the formulation of database design methods that are applicable to a variety of different data models, and (2) the development of techniques to translate programs and data between dissimilar data models. In this paper, we briefly describe how high level abstraction has been applied to these problems. The use of abstraction in database systems is related to the application of abstraction techniques in programming languages and artificial intelligence research.

Heterogeneous databases and high level abstraction

A heterogeneous database management system combines multiple dissimilar models of data within a single integrated system. The objective is to allow a user to access data independently of how it is actually organized. For example, a user may access a database as though it were stored relationally (i.e., in tables) [CODD70], even though it is actually stored as a CODASYL/DBTG or network database [CODA71]. In addition, different subpieces of the database may be organized under different data models. The heterogeneous database system must present these to the user as an integrated whole. The user's model of his data may be different from any of the models chosen to implement it. Rather than construct a new database system from scratch, we are interested in constructing a heterogeneous system out of existing systems. The key difficulties with this approach are: (1) the formulation of database design methods that are applicable to a variety of different data models, and (2) the development of techniques to translate programs and data between dissimilar data models. In this paper, we briefly describe how high level abstraction has been applied to these problems. The use of abstraction in database systems is related to the application of abstraction techniques in programming languages and artificial intelligence research.