A comparative study of transaction management services in multidatabase heterogeneous systems

Multidatabases are being actively researched as a relatively new area in which many aspects are not yet fully understood. This area of transaction management in multidatabase systems still has many unresolved problems. The problem areas which this dissertation addresses are classification of multidatabase systems, global concurrency control, correctness criterion in a multidatabase environment, global deadlock detection, atomic commitment and crash recovery. A core group of research addressing these problems was identified and studied. The dissertation contributes to the multidatabase transaction management topic by introducing an alternative classification method for such multiple database systems; assessing existing research into transaction management schemes and based on this assessment, proposes a transaction processing model founded on the optimal properties of transaction management identified during the course of this research.ComputingM. Sc. (Computer Science

Concurrency Control in Multidatabases

Computer Science

Protocols for Integrity Constraint Checking in Federated Databases

A federated database is comprised of multiple interconnected database systems that primarily operate independently but cooperate to a certain extent. Global integrity constraints can be very useful in federated databases, but the lack of global queries, global transaction mechanisms, and global concurrency control renders traditional constraint management techniques inapplicable. This paper presents a threefold contribution to integrity constraint checking in federated databases: (1) The problem of constraint checking in a federated database environment is clearly formulated. (2) A family of protocols for constraint checking is presented. (3) The differences across protocols in the family are analyzed with respect to system requirements, properties guaranteed by the protocols, and processing and communication costs. Thus, our work yields a suite of options from which a protocol can be chosen to suit the system capabilities and integrity requirements of a particular federated database environment

Transactional actors in cooperative information systems

Transaction management in advanced distributed information systems is a very important issue under research scrutiny with many technical and open problems. Most of the research and development activities use conventional database technology to address this important issue. The transaction model presented in this thesis combines attractive properties of the actor model of computation with advanced database transaction concepts in an object-oriented environment to address transactional necessities of cooperative information systems. The novel notion of transaction tree in our model includes subtransactions as well as a rich collection of decision making, chronological ordering, and communication and synchronization constructs for them. Advanced concepts such as blocking/ non_blocking synchronization, vital and non_vital subtransactions , contingency transactions, temporal and value dependencies, and delegation are supported. Compensatable subtransactions are distinguished and early commit is accomplished in order to release resources and facilitate cooperative as well as longduration transactions. Automatic cancel procedures are provided to logically undo the effects of such commits if the global transaction fails. The complexity and semantics-orientation of advanced database applications is our main motivation to design and implement a high-level scripting language for the proposed transaction model. Database programming can gain in performance and problem-orientation if the semantic dependencies between transactions can be expressed directly. Simple and flexible mechanisms are provided for advanced users to query the databases, program their transactions accordingly, and accept weak forms of semantic coherence that allows for more concurrency. The transaction model is grafted onto the concurrent obj ect-oriented programming language Sather developed at UC Berkeley which has a nice high-level syntax, supports advanced obj ect-oriented concepts, and aims toward performance and reusability. W have augmented the language with distributed programming facilities and various types of message passing routines as well as advanced transactions management constructs . The thesis is organized in three parts. The first part introduces the problem, reviews state of the art, and presents the transaction model. The second part describes the scripting language and talks about implementation details. The third part presents the formal semantics of the transaction model using mathematical notations and concludes the thesis

Integrity Constraint Checking in Federated Databases

A federated database is comprised of multiple interconnected databases that cooperate in an autonomous fashion. Global integrity constraints are very useful in federated databases, but the lack of global queries, global transaction mechanisms, and global concurrency control renders traditional constraint management techniques inapplicable. The paper presents a threefold contribution to integrity constraint checking in federated databases: (1) the problem of constraint checking in a federated database environment is clearly formulated; (2) a family of cooperative protocols for constraint checking is presented; (3) the differences across protocols in the family are analyzed with respect to system requirements, properties guaranteed, and costs involved. Thus, we provide a suite of options with protocols for various environments with specific system capabilities and integrity requirement

Myriad: Design and implementation of a federated database prototype

This paper describes our experiences in the design and implementation of Myriad, and in the project management. Special emphasis is given to discussing design alternatives and their impact on Myriad. This paper also presents the software engineering principles and the project management techniques we used in developing Myriad and the lessons we learned. We believe these lessons would be useful for practitioners who wish to develop a similar syste

Superdatabases for Composition of Heterogeneous Databases

Superdatabases are designed to compose and extend databases. In particular, superdatabases allow consistent update across heterogeneous databases. The key idea of superdatabase is hierarchical composition of element databases. For global crash recovery, each element database must provide local recovery plus some kind of agreement protocol, such as two-phase commit. For global concurrency control, each element database must have local synchronization with an explicit serial order, such as two-phase locking, timestamps, or optimistic methods. Given element databases satisfying the above requirements, the superdatabase can certify the serializability of global transactions through a concatenation of local serial order. Combined with previous work on heterogeneous databases, including unified query languages and view integration, now we can build heterogeneous databases which are consistent, adaptable, and extensible by construction

Transaction management in mobile multidatabases.

This dissertation studies transaction management in the mobile Multidatabase environment. That is, it studies the management of transactions within the context of the mobile and Multidatabase environments. Two new transaction management techniques for the mobile Multidatabase environment i.e., the PS and Semantic-PS techniques are proposed. These techniques define two now states (Disconnected and Suspended) to address the disconnectivity of the mobile user. A new Partial Global Serialization Graph algorithm is introduced to verify the isolation property of global transactions. This algorithm verifies the serializability of a global transaction by constructing a partial global serialization graph. This algorithm relies on the propagation of (serialization) information to ensure that the partial graph contains sufficient information to verify serializability of global transactions. The unfair treatment of mobile transactions due to their prolonged execution time is minimized through pre-serialization. Pre-serialization allows mobile transactions to establish their serialization order prior to completing their execution.The Internet and advances in wireless communication technology have transformed many facets of the computer environment. Virtual connectivity through the internet has lead to a new genre of software systems, i.e., cooperating autonomous systems---systems that cooperate with each other to provide extended services to the user. Multidatabase systems---a set of databases that cooperate with each other in order to provide a single logical view of the underlying information---is an example of such systems. Advances in wireless communication technology dictate that the services available to the wired user be made available to the mobile user.Finally, analytical evaluation and simulation is carried out to study the performance of these techniques and to compare their performance to that of the Kangaroo [DHB97] technique. Although the PS and Semantic-PS techniques enforce the isolation property, the evaluation results establish that the service time for these techniques in not significantly greater than that of the Kangaroo technique. In addition, the simulation establishes that pre-serialization effectively minimizes the unfair treatment of mobile transactions

Towards interoperability in heterogeneous database systems

Distributed heterogeneous databases consist of systems which differ physically and logically, containing different data models and data manipulation languages. Although these databases are independently created and administered they must cooperate and interoperate. Users need to access and manipulate data from several databases and applications may require data from a wide variety of independent databases. Therefore, a new system architecture is required to manipulate and manage distinct and multiple databases, in a transparent way, while preserving their autonomy. This report contains an extensive survey on heterogeneous databases, analysing and comparing the different aspects, concepts and approaches related to the topic. It introduces an architecture to support interoperability among heterogeneous database systems. The architecture avoids the use of a centralised structure to assist in the different phases of the interoperability process. It aims to support scalability, and to assure privacy and nfidentiality of the data. The proposed architecture allows the databases to decide when to participate in the system, what type of data to share and with which other databases, thereby preserving their autonomy. The report also describes an approach to information discovery in the proposed architecture, without using any centralised structure as repositories and dictionaries, and broadcasting to all databases. It attempts to reduce the number of databases searched and to preserve the privacy of the shared data. The main idea is to visit a database that either containsthe requested data or knows about another database that possible contains this data