30 research outputs found
Schema architecture and their relationships to transaction processing in distributed database systems
We discuss the different types of schema architectures which could be supported by distributed database systems, making a clear distinction between logical, physical, and federated distribution. We elaborate on the additional mapping information required in architecture based on logical distribution in order to support retrieval as well as update operations. We illustrate the problems in schema integration and data integration in multidatabase systems and discuss their impact on query processing. Finally, we discuss different issues relevant to the cooperation (or noncooperation) of local database systems in a heterogeneous multidatabase system and their relationship to the schema architecture and transaction processing
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
Flexible Transaction Dependencies in Database Systems
Numerous extended transaction models have been proposed in the literature to overcome the limitations of the traditional transaction model for advanced applications characterized by their long durations, cooperation between activities and access to multiple databases (like CAD/CAM and office automation). However, most of these extended models have been proposed with specific applications in mind and almost always fail to support applications with slightly different requirements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44828/1/10619_2004_Article_270346.pd
Query processing of geometric objects with free form boundarie sin spatial databases
The increasing demand for the use of database systems as an integrating
factor in CAD/CAM applications has necessitated the development of database
systems with appropriate modelling and retrieval capabilities. One essential
problem is the treatment of geometric data which has led to the development of
spatial databases. Unfortunately, most proposals only deal with simple geometric
objects like multidimensional points and rectangles. On the other hand, there has
been a rapid development in the field of representing geometric objects with free
form curves or surfaces, initiated by engineering applications such as mechanical
engineering, aviation or astronautics. Therefore, we propose a concept for the realization
of spatial retrieval operations on geometric objects with free form
boundaries, such as B-spline or Bezier curves, which can easily be integrated in
a database management system. The key concept is the encapsulation of geometric
operations in a so-called query processor. First, this enables the definition of
an interface allowing the integration into the data model and the definition of the
query language of a database system for complex objects. Second, the approach
allows the use of an arbitrary representation of the geometric objects. After a
short description of the query processor, we propose some representations for free
form objects determined by B-spline or Bezier curves. The goal of efficient query
processing in a database environment is achieved using a combination of decomposition
techniques and spatial access methods. Finally, we present some experimental
results indicating that the performance of decomposition techniques is
clearly superior to traditional query processing strategies for geometric objects
with free form boundaries
Object-oriented querying of existing relational databases
In this paper, we present algorithms which allow an object-oriented
querying of existing relational databases. Our goal is to provide an improved query
interface for relational systems with better query facilities than SQL. This
seems to be very important since, in real world applications, relational systems
are most commonly used and their dominance will remain in the near future. To
overcome the drawbacks of relational systems, especially the poor query facilities
of SQL, we propose a schema transformation and a query translation algorithm.
The schema transformation algorithm uses additional semantic information to enhance
the relational schema and transform it into a corresponding object-oriented
schema. If the additional semantic information can be deducted from an underlying
entity-relationship design schema, the schema transformation may be done
fully automatically. To query the created object-oriented schema, we use the
Structured Object Query Language (SOQL) which provides declarative query facilities
on objects. SOQL queries using the created object-oriented schema are
much shorter, easier to write and understand and more intuitive than corresponding
S Q L queries leading to an enhanced usability and an improved querying of
the database. The query translation algorithm automatically translates SOQL queries
into equivalent SQL queries for the original relational schema
TOPAZ:a tool kit for the assembly of transaction managers for non-standard applications
'Advanced database applications', such as CAD/CAM, CASE, large AI applications or image and voice processing, place demands on transaction management which differ substantially from those in traditional database applications. In particular, there is a need to support 'enriched' data models (which include, for example, complex objects or version and configuration management), 'synergistic' cooperative work, and application- or user-supported consistency. Unfortunately, the demands are not only sophisticated but also diversified, which means that different application areas might even place contradictory demands on transaction management. This paper deals with these problems and offers a solution by introducing a flexible and adaptable tool kit approach for transaction management
Transaction execution in multidatabase systems
Ankara : Department of Computer Engineering and Information Science and Institute of Engineering and Science, Bilkent Univ., 1996.Thesis (Master's) -- Bilkent University, 1996.Includes bibliographical references leaves 80-82.Most work in the multiclatabase systems (MDBSs) area has focused on the
issues of transaction management and concurrency control. It is difficult to
implement traditional transaction management techniques in a MDBS due to
the heterogeneity and autonomy of the connected local sites. In this thesis,
we present a new transaction execution model that captures the formalism
and semantics of various extended transaction models and adopts them to a
MDBS environment. The proposed model covers nested transactions, various
dejjendenc}' types among subtransactions, and commit-independent transactions.
The execution model does not make any assumption regarding the concurrency
control protocols executed at the local sites connected to the MDBS.
VVe also present a detailed simulation model of a MDBS to aiiiilyze the
performance of the proposed model. The performances of both the traditional
transaction model and the proposed transaction model are evaluated under
a range of workloads and system configurations. The performance impact of
global transactionsā behavior on local transactions is also discussed.DevirmiÅ, TimuƧinM.S
Compensation methods to support cooperative applications: A case study in automated verification of schema requirements for an advanced transaction model
Compensation plays an important role in advanced transaction models, cooperative work and workflow systems. A schema designer is typically required to supply for each transaction another transaction to semantically undo the effects of . Little attention has been paid to the verification of the desirable properties of such operations, however. This paper demonstrates the use of a higher-order logic theorem prover for verifying that compensating transactions return a database to its original state. It is shown how an OODB schema is translated to the language of the theorem prover so that proofs can be performed on the compensating transactions
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