Datasheet

Database Engine
The Database Engine is the primary component of SQL Server 2005. It is the Online Transaction
Processing (OLTP) engine for SQL Server, and has been improved and enhanced tremendously in this
version. The Database Engine is a high-performance component responsible for the efficient storage,
retrieval, and manipulation of relational and Extensible Markup Language (XML) formatted data.
SQL Server 2005’s Database Engine is highly optimized for transaction processing, but offers exceptional
performance in complex data retrieval operations. The Database Engine is also responsible for the con-
trolled access and modification of data through its security subsystem. SQL Server 2005’s Database
Engine has many major improvements to support scalability, availability, and advanced (and secure)
programming objects:
❑ Physical partitioning of tables and indexes — Tables and indexes can now be physically partitioned
across multiple file groups consisting of multiple physical files. This dramatically improves the
performance of data retrieval operations and maintenance tasks that are executed against very
large tables. (See Chapter 5 for more information.)
❑ Data Definition Language (DDL) triggers — DDL triggers can be used to execute commands and
procedures when DDL type statements are executed. In the past, modifications to the database
could go undetected until they caused an application to fail. With DDL triggers, a history of all
actions can be easily recorded or even prevented. DDL triggers can be placed at the server or
database level.
❑ Enhanced variable-length data types — A new
MAX keyword has been added to varchar,
nvarchar, and varbinary data types that allow the allocation of up to 2GB of space for large
object variables. One of the chief advantages of this addition is the ability to use large value
types in the declaration and use of variables.
❑ XML data type—The new XML data type enables the storage of well-formed and schema-
validated XML data. It also brings rich support in the form of XML data type methods,
along with enhancements to
OPENXML and FOR XML T-SQL commands.
❑ Multiple Active Result Sets (MARS) — MARS allows for clients to maintain more than one data
request per connection. For example, in the past, if a connection was opened in an application,
only one data reader could be opened to retrieve data from the database. To open another data
reader, the first one had to be closed. With MARS, this limitation is removed.
❑ Structured error handling — T-SQL now includes the ability to perform structured error handling
in the form of
TRY and CATCH commands that remove the necessity of repeated checks for errors
in scripts, and the ability to elegantly handle any errors that do occur.
❑ Common Table Expressions (CTE) — Microsoft has extended the American National Standards
Institute (ANSI) compliance of T-SQL by including the ability to use the CTE object. CTEs are
extraordinarily useful in the creation of efficient queries that return hierarchical information
without the need for using lengthy and complicated recursive sub-queries.
❑ Security enhancements — SQL Server’s security architecture has been enhanced considerably with
the ability to enforce account policies on SQL Server logins. Other additions to SQL Server’s
security architecture include the control of execution context and the ability to create encryption
keys and certificates to control access and guarantee the integrity of database objects through
the use of digital signatures. See Chapter 6 for more information.
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