(Transfer from "Delphl5.x ADO / MTS / COM Advanced Program Design" Li Wei) Microsoft provides several different data access technologies in the Windows platform. These different data access technologies have their characteristics and causes. Microsoft has also learned many experience from achieving these different data access technologies, and developing a new generation according to these experiences, ADO is a very good example. Now let's take a look at each technique from a variety of technical perspectives, it is to access what kind of data source. 1.ODBC 1992 Microsoft and Sybase, Digital jointly developed an ODBC standard interface to access a variety of different databases in a single ODBC API. Subsequent ODBC has gradually become a standard data access technology for many database vendors and Third-Party support. ODBC supports a wide database with the range of the industry's standard specification X / Open Call-Level Interface (CLI) and ISO / IEC9075-3 Call-Level Interface (SQL / CLI). Although ODBC is not effective in the initial version, it is also derogatory to people. However, as Microsoft constantly improving ODBC, the ODBC driver's function is also getting more and complete. By current, ODBC is already a stable and perform efficiency data access engine. However, ODBC only supports relational databases, as well as the traditional database data type, and only in the form of a C / C language API, so it cannot meet the increasingly complex data access applications, and the scripting language cannot be used. Therefore, in addition to ODBC, Microsoft has introduced other data access technologies to meet the needs of the programmer. 2. DAO 1993 Microsoft In order to allow programmers to access the Access database, use Ole Automation technology to encapsulate Jet Engine. These OLE AutomationObject that uses Jet Engine access Access database is called Data Access Object (DAO). DAO can access XBase's database and Excel files, and capable of combining ODBC access relationship databases. However, DAO is the main design purpose to access the Access database, so DAO is very efficient when accessing the Access database, but is not good when accessing other data sources. At present, DAO has slowly approached maintenance, so it is recommended that you do not use DAO in new projects. 3. RDO is not good when DAO is incorporated in conjunction with an ODBC access database, so in 1995, Microsoft also encapsulates ODBC APIs in Ole Automation technology, allowing programmers to access relational databases. This data access technology is called Remote Data Object (RDO). Microsoft launches RDO because ODBCAPI is a very complex API. Many programmers cannot use the ODBC API to develop applications, so Microsoft allows programmers to make programmers more simple access data in a simplified RDO object. In addition, various relational databases can also be accessed by RDO, VB, and scripting languages. However, the RDO has also been gradually abandoned, so it is recommended not to use RDO in the new item Chapter 1, ADO / MTS / COM and distributed multi-layer architecture 3 download, after all, RDO can only be considered a transitional data. Access solution. 4. OLE-DB As the data source is increasing, the current application is likely to obtain data from different data sources, processes, and then output the processed data to another data source. What is more troublesome is that these data sources may not be a traditional relational database, which may be an eXcel file, email, or electronic signature information on the Internet / Intranet.
