數(shù)據(jù)庫管理系統(tǒng)外文翻譯-管理系統(tǒng)-在線瀏覽
2025-03-24 11:57本頁面
【正文】 proach that’s 大連交通大學 2021 屆本科生畢業(yè)設(shè)計 (論文 )外文文獻翻譯 3 expected to be widely implemented in the future. 5. Physical structure. People visualize or structure data in logical ways for there Own purposes. Thus, records R1 and R2 may always be logically linked and processed in sequence in one particular application. However, in a puter system it’s quite possible that these records that are logically contiguous in one application are not physically stored together. Rather, the physical structure of the I/O and storage devices techniques used, but also on the different logical relationships that users may assign to the data found on R1 and R2. For example, R1 and R2 may be records of credit customers who have shipments send to the same block in the same city every two weeks. From the shipping department manager’s perspective, then, R1 and R2 are sequential entries on a geographically anized shipping report. But may be identified, and their accounts may be processed, according to their account numbers which are widely separated. In short, then the physical location of the stored records in many puterbased information systems is invisible to users. During the past five years, Microsoft has promoted Data Access Objects (DAO), and then Remote Data Objects (RDO), and now ActiveX Data Objects (ADO) as the primary data access technology for Visual Basic developers. It seems that Microsoft has been pushing a different data access technology with each successive version of Microsoft Visual Studio. Today, new versions of ADO are available on Microsoft39。s Web site and ship with other products and technologies, such as Microsoft Windows 2021, Microsoft Windows NT 4 Service Packs, Microsoft Inter Explorer versions 3 and later, Microsoft SQL Server Service Pack 5 and SQL Server 7, Microsoft Office 2021, and even Microsoft Expedia Streets amp。s take a quick glance at ADO39。s performance with these large database systems. Others plain that DAO doesn39。s performance and access limitations, developers who wanted to work with SQL Server and Oracle databases generally sought other options. Remote Data Objects Microsoft provided another option in RDO, which originally released with Visual Basic 4 Enterprise Edition. RDO39。t the problem for most programmers learning RDO: the nuances inherited from the ODBC API posed the greatest obstacles. Suddenly, programmers had to bone up on cursors and bookmarks. They had to learn many of the ins and outs of specific database systems. Does the error message The connection is busy with results from another hstmt ring any bells out there? If you try to do the impossible on an ODBC connection to your database, RDO won39。ll get that error. DAO hid the problem from you by automatically creating another connection to your database to perform the action you requested. Another challenge that RDO posed for programmers accustomed to writing DAO code was that RDO lacked many of DAO39。m at a loss to name a single significant feature available in RDO that was not available in ADO in one form or another. (I39。 a great way to find such features is to make a statement like that in a book like this.) With the release of version , ADO and its supporting libraries began offering nearly all features available in DAO. DDL libraries were added to ADO in version to provide functionality similar to functions available with DAO, such as Create Table, Create Field, and Create Index. Microsoft J
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