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Introducing Sybase Workplace SQL Server

Chapter 1: Overview of Workplace SQL Server

Relational Database Management Systems

Relational Database Management Systems

A relational database management system (RDBMS) is a system for storing and retrieving data in which the data is represented in two-dimensional tables. In early relational systems, tables were called relations. A relational database consists of a collection of tables that store interrelated data.

Tables

Figure 1-1 shows portions of tables that you might create in a relational database storing related data about books¾ called titles, authors, publishers, and titleauthor.

Figure 1-1: Tables in a database

Each table in the database holds information about different things¾books, publishers, and authors. But some information in each table overlaps with information in another table¾by design. Columns that appear in more than one table and that link the tables together are called keys. Keys, which are discussed in more detail in "Key", allow you to retrieve information that is distributed over multiple tables.

For example, you might want information about books published by Marjorie Greene, which spans the authors and the titles tables. Figure 1-2 shows the key columns for our sample databases and how they allow you to retrieve the correct data from the tables.

Figure 1-2: Retrieving data across tables using key columns

One advantage of relational databases is that they allow you to set up multiple tables, a structure that eliminates redundancy and possible inconsistencies caused by that redundancy. For example, both the sales and accounts payable departments might enter and look up information about publishers. In a relational database, the information about publishers only needs to be entered once, in a table that both departments can access.

Defining how tables represent a body of information, determining how the data should be distributed among the tables, and deciding what keys are needed to define the relationships are the subjects of logical design. Sound database design is the key factor in realizing SQL Server's performance potential and makes your database easy to maintain and update. Many excellent books are available on this subject. The Practical SQL Handbook (Bowman, Emerson, and Damovsky, Addison-Wesley, 1993) offers a clear introduction to logical database design, and it specifically relates the issues to a SQL Server context. (See "Designing Databases".)

SQL

SQL (Structured Query Language) is the foundation for entering data in and retrieving data from the server. SQL is the database language designed for the RDBMS model, which makes it easy to set up, use, and maintain a relational database. This is in contrast to database systems in previous computing models, which required large IS departments to be involved in data requests. An excellent reference for learning SQL is the LAN Times Guide to SQL (Groff and Weinberg, Osborne McGraw-Hill, 1994).

End users need not learn SQL in order to access data, however¾in most systems, purchased or developed GUI client software does the job of translating user requests into SQL. Software called application programming interfaces (APIs) or libraries installed on the clients allow applications to communicate with the RDBMS.

Sybase's enhanced version of SQL is called Transact-SQL (see "Transact-SQL").

Auxiliary Facilities of SQL Server's RDBMS

In addition to storing and retrieving data, SQL Server provides a number of auxiliary facilities for managing the relational databases. These include programs for starting and stopping the server, for backing up and restoring data, for copying data between a database and a file system, for authenticating users of the server and the databases, for managing the physical devices on which the data is stored, for displaying system messages in different languages, for storing and preprocessing a reusable procedure or set of procedures, and so forth. Together with the basic storage and retrieval capabilities, these facilities make up SQL Server's relational database management system.