Integration of Heterogeneous Database
Resource integration of heterogeneous database interoperability federated database 1. Introduction Heterogeneous database interoperability issues as a database research in the field hot and difficult issues at home and abroad, academic and industrial sectors have attracted wide attention. Since the 20th century, since the 80’s, many foreign companies and research institutes to the integration of heterogeneous databases to conduct a large number of studies and achieved a lot of results, but the domestic research on the integration of heterogeneous databases is still in its early stage.
The concept of heterogeneous database interoperability Heterogeneous Databases (Heterogeneous Database) database technology integration is a completely centralized logical focus, physical distribution (traditional distributed database) as well as the logical distribution, physical distribution (heterogeneous database) the results of this development process, but also take into account existing systems self – Sexual and achieve the reality of the new data-sharing needs of effective means.
Heterogeneous database heterogeneous features include two levels: system level and language level, heterogeneous, mainly reflected in the following areas. * Computer architecture, heterogeneous: respectively, each participating database can run on mainframes, minicomputers, workstations, PC or embedded system. * Heterogeneous operating systems: each database system is based on the operating system can be Unix, Windows NT, Linux and so on. of heterogeneous database management systems: a conceptual model of heterogeneous database.
There are levels, network, relational and object-oriented 4; the other is the physical model of heterogeneous database: the conceptual model refers to the same but the data structure is different, such as the relationship between Oracle and SQL Server the same type, but the structure is different. The realization of interoperability of heterogeneous database consists of three functional elements: 1. o provide users with powerful and flexible operation of interoperable visual interface through which users can intuitively transparent access to multiple heterogeneous databases; 2. to provide high-level language database access call-level interface, as call-level interface, designers can achieve the level depending on the specific situation may be clear; 3. to support environmental and open, if possible, should also support the implementation language open.
Heterogeneous database system aimed at achieving data between different databases of information resources, hardware and human resources of the combined and shared. Heterogeneous database systems integration is to a different database systems, operating systems, different operating platforms of different or the blocking of different underlying network, enabling users to heterogeneous database system can be regarded as an ordinary database system, with their own familiar data-processing language to access the database, as access to a database system, like its transparent operation. . to achieve heterogeneous database interoperability approach
The face of heterogeneous database interoperability requirements, mainly from the two simultaneous efforts: First, establish standards, that is to establish a unified database of norms, standards eliminate the imperfect system resulting from the differences between various databases; second is to build interoperability of heterogeneous database platforms, achieve transparent access to multiple heterogeneous databases.
With a database interoperability issues in-depth study, based on different perspectives, many researchers have put forward a viable heterogeneous database interoperability channel, these channels to achieve interoperability of the depth, breadth and height vary both in their respective to adapt to the specific environment and needs. The core idea of the database from heterogeneous starting to realize interoperable way to be summarized in two categories. 3. 1 system-level heterogeneous interoperability
DBMS system for heterogeneous network environment database interoperability, the main there are four means of realization. * Database Gateway (Database Gateway) Database Gateway is a repeater; it can provide application-level integration of heterogeneous database tools. Gateway’s primary role is to convert and communications. Database Gateway can establish more stable and transparent database interoperability, but its shortcomings are obvious. Such as do not care about how to shield the heterogeneity between databases and does not upport transaction processing, resource redundancy, the user is limited in the database vendor cannot arbitrarily select the client platform and target database and so on.
Database Gateway compared to more public agreements, scalability and openness, can better realize the transparency of heterogeneous database access, support for multiple network protocols and multiple client platforms, heterogeneous database interoperability to achieve an effective way to one. Public License / data transfer protocol drawback is that the agreement itself inefficiencies brought about by speed. * Public Programming Interface Common Programming Interface, including customer application programming interface (CAPI) and server application programming interface (SAPI).
CAPI is a set of process libraries, usually resides on the client, through the back-end load specific drivers to access different databases. SAPI provides an application programming interface to control the server and client application requests and the interaction between the target database. Such as Microsoft, ODBC, Oracle’s SQL * NET, as well as IDAPI. Its advantages are: By providing a unified call-level interface, allowing users to remove the application database with the changes of the pain; through the API allows applications to manipulate data in the database directly.
Database access API’s weaknesses are: a database for each one needs to have one with their corresponding drivers; due to different drivers supported by the data types and operations on the data are not the same as its fully transparent access to heterogeneous database capacity is limited; to achieve efficiency in over-reliance on the driver and the driver of the standard grammar into the corresponding database command syntax to spend a lot of time.
Middleware is in the application and the application is located between the way the inner workings of the system software, and its basic idea is that in all the back-end data sources and front-end application to establish a layer of abstraction between. The application and system software at a lower level details of the attachment and complexity of segregation, so that application developers to deal only with certain types of a single API, and other details can be handled by the middleware.
This allows the system to the operation of each of the different data sources into a single operation of the middleware, while the later pairs of middleware for heterogeneous processing. The use of heterogeneous database integration middleware technology to solve the problem, this will bring a lot of system integration benefits. This is because the middleware can not only make front-end user access to heterogeneous back-end databases to achieve transparency and to ensure the openness of the access interface, so you can make the system function in the future expansion easier.
To access the database through the middleware Another advantage is that all client requests are sent to the middleware, reduce the burden on the database server to ensure that the database server’s performance does not decrease. Meanwhile, the adoption of middleware greatly enhance the maintainability of the system, a logic within the system changes, as long as the change in the corresponding middle-tier processing, front user interface does not require any changes, so will be greatly reduced the system maintenance costs. 3. heterogeneous data structure and semantic-level interoperability.
At present, the data structure and semantics for a heterogeneous database interoperability research are closely coupled and loosely coupled two kinds of thinking, specifically embodied in the multi-database systems, federated database systems and distributed database systems are three ways. 1. Multi-database system The so-called multi-database system is a way to accept and accommodate multiple heterogeneous database systems, allowing the various heterogeneous database of ‘autonomy’.
Multi-database system is a broad concept, as opposed to, such as a centralized database systems or distributed database system that logically have the same management system for the purposes of its diversity and distribution in order for the main features. Multiple refers to the difference between its number of centralized or distributed database system; distribution refers to the data in different venues of database systems, by the respective management systems to manage. Multi-database technology, the goal is to achieve the interoperability between multiple databases, to address the resource-sharing database, to find a technical way.
Commonly used distributed, heterogeneous, autonomous features as a measure to characterize the three multi-database system. Using this method, users need to explicitly specify the database to be accessed. Multi-database system uses a bottom-up methods. 2. Distributed Database (Distributed Database) The basic idea of distributed database is to abandon the original database system in a networked environment to establish the distribution of the database system, architecture, transaction processing models, and other aspects of re-engineering in order to address information sharing and interoperability issues.
Distributed database system is divided into homogeneous and heterogeneous distributed database distributed database. Such as Oracle, Sybase, Informix and so on are all homogeneous distributed database system, the realization of such systems is relatively easier. Heterogeneous distributed database management systems are mostly some of the existing database management system based on the realized. 3. Federal Database (Federated Database)
Federated database system is a distributed database network technology and the inevitable result of technological development, it is by a group to coordinate the work, but also the independent and autonomous component databases. It can be the original non-distributed, they can be distributed, with a distributed, autonomous, heterogeneous three characteristics. Federated database and distributed database systems are distinguished: a distributed database system while physically dispersed, but because there is a unified data model and the global data model, so it is logically centralized, so users feel is a complete database.
Obviously, such systems can be used for a specific area of the system, but not suitable for different areas of integration between heterogeneous systems. On the contrary, the Federal-style database system is composed of loosely coupled at different nodes of the heterogeneous distribution of members of the database structure, among the members of the Federation as a loose combination. Constitute the members of the Federation can be a centralized database, it can be a distributed database, they can be required (by some combination of) joined the Federation, or as needed secede.
Federated databases are not global schema, each subsystem (ie, the federal member) according to their own needs to develop their own data model. Data-sharing among its members, relations, through a consultation to determine the input / output mode to create a single member of the right to refuse or to allow other members of the nodes that access to it. Therefore, it can support multi-database systems are distributed, heterogeneous and autonomous, thus producing satisfactory integration.
Interoperability of heterogeneous database technology makes database in the original technology to play an important role, in the future new areas of application also has important implications, such as the Earth Observing System EOSDIS, e-commerce, healthcare information systems, digital publishing, collaborative design, etc.