SQL和SQL服务器（一）:2012年计算机一三四级考试考试:三级考试-百考试题网

　　IBM invented a computer language back in the 1970s designed specifically for database queries called SEQUEL；those letters stand for Structured English Query Language．Over time，the language has been added to so that it is not just a language for queries，but can also build databases and manage the database engine’s security．IBM released SEQUEL into the public domain，where it became known as SQL．Because of this heritage you can pronounce it“sequel”or spell it out“S-Q-L．”There are various versions of SQL used in today’s database engines．Microsoft SQL Server uses a version called Transact-SQL，or T-SQL，which stands for Transaction SQL．

　　1．What Is SQL Server?

　　SQL Server is a client／server relational database management system（RDBMS）that uses Transact-SQL to send requests between a client and SQL Server．

　　2．Client／Server Architecture

　　The terms client，server，and client / server can be used to refer to very general concepts or to specific items of hardware or software．At the most general level，a client is any component of a system that requests services or resources from other components of a system．A server is any component of a system that provides services or resources to other components of a system．
For example，when you print a document from your workstation on a network，the workstation is the client and the machine that does the print spooling is the server．[1]
Any client／server data-based system consists of the following components：
•. The server一A collection of data items and supporting objects organized and presented to facilitate services，such as searching，sorting，recombining，retrieving，updating，and analyzing data．The database consists of the physical storage of data and the database services．All data access occurs through the server；the physical data is never accessed directly by the client．
．The client — A software program that might be used interactively by a person or that could be an automated process．This includes all software that interacts with the server，either requesting data from or sending data to the database．Examples are management utilities（those that are part of the SQL Server product as well as those bought separately），ad hoc query and reporting software，custom applications，off-the-shelf applications，and Web server-based applications．[2]
•. The communication between the client and the server一The communication between the client and the server depends largely on how the client and server are implemented．Both physical and logical layers of communication can be identified．[3]
When you communicate with someone using the telephone，the telephone system is the physical layer and a spoken natural language is the logical layer of communication．For a data-based system，the physical layer can be a network if the server and the client are on different computers．It can be interprocess communication if the server and the client are on the same computer．The logical communication structure of the physical layer may be low-level operating system calls，a proprietary data access language，or the open structured query language（SQL）．

　　3．SQL Server Platforms

　　SQL Server runs on the operating systems shown in Fig. 7-4．The SQL Server version 7 server software runs only on the Windows 32-bit API-based operating systems，but you can use all of the operating system platforms to create and execute client applications．