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Discovering SQL: A Hands-On Guide for Beginners by Alex Kriegel

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2

Breaking and Entering: Structured Information

Let's take a closer look at the whirlwind of concepts introduced in the first chapter: database, database object, table, schema, and instance. Despite being around for a long time, there is still a fair amount of confusion regarding what a relational database management system (RDBMS) is because each one has somewhat different ideas on the subject. Yet you have to have a clear understanding of the concepts behind the terminology. Your data will live inside these objects, tucked into tables, and bound by the rules.

In the broadest terms, a database is a logical abstraction that describes a collection of interrelated objects managed as a unit. This would accommodate Microsoft Access, which for all intents and purposes is a file; and OpenOffice BASE, which is a pass-through to another relational database with an embedded Hyper Structured Query Language Database (HSQLDB) engine as a default. In Microsoft SQL Server, PostgreSQL, and MySQL contexts, a database is a collection of objects under common ownership managed by the software instance; whereas for Oracle, DB2, and DB2 UDB a database is a bunch of files managed by the software. What Microsoft calls database, Oracle refers to as schema; both are almost identical to a user in Oracle's context.

This is the bad news, but there is good news, too. On a fundamental level, we are dealing with physical files and the processes that manage them, and the particulars of them are primarily of ...

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