This whitepaper explains the key differences between Microsoft® SQL Server™ 2005 databases and Oracle databases. It compares SQL Server and Oracle database architecture and provides information on the newest features in SQL Server 2005. This paper is intended for Oracle professionals who want to leverage their Oracle knowledge to manage SQL Server or prepare to migrate an Oracle database to SQL Server 2005. Other topics discussed in this white paper include backups, database security, management options and high availability options.

Database Architecture
In Oracle, a database refers to the entire Oracle RDBMS environment and includes the following components:
• Oracle database processes and buffers (instance).
• SYSTEM tablespace containing one centralized system catalog, which is made up of one or more datafiles.
• Other optional tablespaces as defined by the database administrator (DBA), each made up of one or more datafiles.
• Two or more online Redo Logs.
• Archived Redo Logs (optional).
• Miscellaneous files (control file, Init.ora, Config.ora, and so on).

A database in Microsoft SQL Server 2005 refers to a physical grouping of set of schema objects of a database into one or more physical files. Databases are classified into system-defined database and user-defined database within SQL Server 2005. The system databases consist of the system data and also controls the temporary storage required for application data. The application data is available in a SQL Server user-defined database. An instance of SQL Server can support multiple databases. Applications built using SQL Server can use databases to logically divide business functionality. There can be multiple instances of SQL Server on a single computer. Each instance of SQL Server can contain multiple databases.

Each SQL Server database can support filegroups, which provide the ability to physically distribute the placement of the data. A SQL Server filegroup categorizes the operating-system files containing data from a single SQL Server database to simplify database administration tasks, such as backing up. A filegroup is a property of a SQL Server database and cannot contain the operating-system files of more than one database, although a single database can contain more than one filegroup. After database creation, filegroups can be added to the database.

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