SPECIAL IMPLEMENTATION CONSIDERATIONS - Database Design and Development: An Essential Guide for IT Professionals - page 413

CHAPTER SUMMARY
• Database implementation includes definition of data structures, enabling of
database usage, optimal processing of data requests, and other ancillary tasks
to prepare users.
• Languages are essential for implementation of a database system. These
languages serve two primary purposes—storage of data and usage of data.
• The data definition language (DDL) component defines the data structures and
supports the storage of data.
• The data manipulation language (DML) component enables data retrieval
and data maintenance. Data maintenance consists of addition, deletion, and
modification of data.
• Earlier relational languages include Query-by-Example (QBE), Quel, and
Datalog. These languages contain DDL and DML components.
• Structured Query Language (SQL), a command-driven, declarative, nonproce-
dural language, has evolved as the standard for relational database systems.
• Both ANSI and ISO have adopted and standardized SQL. The process of
standardization and enhancing SQL continues.
• As a DDL, SQL provides statements for the specification of logical and
physical components for the relational database. SQL supports a variety of data
types.
• Data retrieval in SQL is accomplished through an SQL query made up of three
simple clauses or commands—SELECT, FROM, and WHERE.
• SQL has provisions to grant and revoke data access privileges to users. Access
privileges may be granted to users to perform only specific functions such as
data retrieval, data addition, data update, and so on.
• Data access from an application program to a relational database is generally
accomplished in two ways: embedding SQL statements in host language
programs or using an application programming interface (API) consisting of
standard database functions.
• Query processing consists of several steps including the important step of
optimizing the query. Two common approaches for query optimization are
heuristic or rule-based optimization and cost-based optimization.
REVIEW QUESTIONS
1. What is the meaning of implementation of a data model? Which two primary
purposes are accomplished by implementation?
2. How do languages enable implementation of a data model? What is the role
of languages in implementation?
3. Distinguish the functions: data retrieval, data maintenance, and data control.
4. List any four of the overall features of SQL.
5. Name any five data definition statements in SQL. Describe the purpose of
each.