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附录A
Visual Basic in the remote-access database of several
categories of key technologies
Visual Basic Professional Edition is a widely used database programming language, provides a database application of strong support. VB visit to a large database of three categories: the use of data binding controls, the use of variable object database access, direct calls ODBC 2.0 API interface function.
VB of the database structure. VB database is the core structure of Microsoft Jet database engine, JET engine's role is to support a variety of ISAM (Indexed Sequential Access Method, which means access to the order index) data-driven process. Ms JET engine essentially provided: one with ANSI standard parser; query result set for the use of the memory management functions supported by the database with the external interface; application code to provide for the internal interfaces.
VB visit to the principle of the database.1. Code reuse and the efficiency of operation
VB program design, the code should minimize duplication of the development, improve operating efficiency. For example: ODBC data sources through the use of the method of connecting to the database, the database can transform a variety of types of cases, rather than frequent amend the code. VBSQL used by DB-Library to do. VB ODBC interface and access the database is not running the most efficient way. Similarly, the use of ODBC interface with the ADO the efficiency is higher than that of RDO.
2. Realization of a simple, easy maintenance
If a way to achieve it are complex, the project will inevitably lead to the development of a waste of manpower and resources, designed so the application would only support up to more complex or more difficult to maintain. For example: local needs visit ISAM or Jet types of data sources, then use the DAO / Jet, and there is no need to use the method through ODBC. RDC together to achieve more easily than the RDO.
3. Safety principles
This should be based on an environment and conditions. For example, the LAN network security is better than the wide area network, thus the direct use of data controls
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DC, to facilitate the realization of this fast, and wide-area network needs a lot of mistakes capture, such as the RDC as easy to use RDO control error.
Data Access interface function and meaning.
ADC (Advanced Data Connector): advanced data connections. ADO data sources to provide bundled to form the data binding controls on. ADC is a major or through direct access to visit remote OLE DB ADO object of a technology, it also supports major applications in Microsoft's IE browser on the data binding controls. It is specifically for the Web browser-based applications designed.
ADO (Active Data Objects): Active Data Objects. Is DAO / RDO the successor product, ADO \that it contains fewer targets, more properties, methods (parameters), and the incident. ADO is a reality to provide access to various types of data linking mechanism. ADO designed to be a very simple format, the method through ODBC interface with the database. You can use any ODBC data source, that is not suitable for SQL Server, Oracle, Access and other database applications, is also suitable for an Excel spreadsheet, text, graphics and documents without the data file format, is a user-friendly application layer Interface. ADO for Microsoft is the latest and most powerful data access paradigm designed OLE DB, OLE DB for any data source to provide a high-performance, including the relationship between these data sources and non-relational databases, e-mail and file systems, text and graphics, Custom business objects and so on. ADO in a crucial programmed in the use of the Internet for at least the network traffic, and in front-end data sources and the use of at least between the layers, all of which are to provide a lightweight, high-performance interface. Therefore ADO through its internal properties and methods to provide a unified data access interface methods.
DAO (Data Access Objects): data access objects. Is an object-oriented interface. Through DAO / Jet ISAM function can access the database, using the DAO / ODBC Direct functions can be remote RDO function. DAO use of the procedure code is very simple, DAO provide rich cursor (Cursor) type of result sets and non-cursor (Cursor-Less) type of result sets, with DDL (data description language) is very similar to the function. DAO through ODBC like to directly connect to other databases, directly connected to the Access database. DAO ideal for single-application procedures or the use of small-scale local distribution. DAO model is to design the structure of relational database system object class collection. They provide a complete management system for all the attributes and
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methods of operation, including the creation of the database, the definition table, fields and index, the establishment of the relationship between the table, positioning and query the database and other tools.
JET (Joint Engine Technology): data connectivity engine technology. Based on a workstation through the DAO database access mechanism. Although Microsoft Access can be provided by the ODBC driver to visit Jet database, but the driver in the use of these functions be limited. Jet has its own mechanism for collection and processing results and on the same or dissimilar data sources for query processing.
ODBC (Open Database Connectivity): open database connectivity. Heterogeneous database for the visit provides a unified interface. Based on ODBC SQL (Structured Query Language), and regarded it as the standard database access. This interface provides maximum interoperability: an application by a group of generic code to a different database management system. A software developer in the development of client / server applications for the beam will not be a specific database on. ODBC for different database with the appropriate driver is a recognized source of the relationship between the data interface. It fast and light to provide a unified interface and the interface, ODBC to any data source did not make optimization.
ODBC API: database vendors for the program designers to provide direct access to the database for a group function. Note: here like to point out that, although the ODBC API to provide a lot of very convenient and powerful. But generally speaking ODBC API is more difficult to learn and use very prone to error. Although allowed to operate with ODBC API ODBC handler, but still must be careful, if not the proper use ODBC API, may lead to unpredictable errors. For example, if the use of ODBC API code to turn off the connection or the release of these ODBC handle in any one of, or RemoteData control of RDO will be unpredictable. Save ODBC handler for the reserve is also no sense, because they are variable.
ODBC Direct: DAO is a target based on the new DAO mode, its methods and function of the same attributes and RDO. DAO code is used in the presence of the occasion, can be used to access remote data sources.
OLE DB: COM is a model of the database interface. The bottom is a data access interface. Is the third driver for the development of business output data source to ADO technology for the application or C + + developers who develop custom database components. It can handle any type of data. OLE DB application to provide a uniform
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method of data access, regardless of their format and storage methods. In practice, this means that diversity can access presence in the electronic data table, text file or e-mail server, such as Microsoft Exchange of data. OLE DB can not be directly called VB.
RDC (Remote Data Control): remote data access control, the RDO is a data binding
controls. Can export a specific set of results to the data source controls.
RDO (Remote Data Objects): remote data objects. To an ODBC, object-oriented data access interface, and remote data collection target for the use of code to create and operate a remote ODBC database system in various parts provides a framework. Objects and collections have a database describing the various attributes and characteristics of the components used to the method of operation of these components. Can be established between objects and collections, these relations on behalf of the logical structure of the database system. With its easy-to-use DAO style combinations together, provide an interface, the form shows the bottom of all ODBC function and flexibility. RDO ODBC API is a shallow interface. Is designed for remote access relations ODBC data source designed. Although the visit Jet RDO or ISAM database be limited, and it can only be through the existing ODBC driver to access relational database. However, RDO has proved to be many SQL Server, Oracle and other major relational database developers often choose the best interface. RDO to provide access to the storage complex process and the result set more and more complex objects, attributes and methods.
VBSQL: Visual Basic is structured query language. Based on the API is a kind of interface methods, and almost C of DB-Library API the same, VBSQL support only Microsoft's SQL Server. VBSQL fast and light but not the object interface.
VB database access methods. VB there are many ways to access the database, under
normal circumstances is divided into three categories, each category has a lot of ways. Each of the categories listed below, and each category contains the method.
1. Data Control Act
Database binding controls to achieve the data input, display, screening and other interface. Programmers can use the same objects, attributes and methods to deal with a variety of database formats. Can also be changed from one database format to another format, but also in a single query or statements from a number of different databases connect the table.
2. Data Interface law
Some are simple interface application programming interfaces (APIs), some of the