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RELATIONAL DATABASES - Coggle Diagram
RELATIONAL DATABASES
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DATABASE SYSTEMS
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Schemas
A schema
idescription of the data elements in a database, the relationships among them, and the logical model used to organize and describe the data.
The conceptual-level schema
the organization-wide view of the entire database, lists all data elements and the relationships among them.
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The internal-level schema
a low-level view of the database, describes how the data are stored and accessed, including record layouts, definitions, addresses, and indexes.
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DBMS Languages
The data definition language (DDL)
builds the data dictionary, creates the database, describes logical views for each user, and specifies record or field security constraints.
The data manipulation language (DML)
changes database content, including data element creations, updates, insertions, and deletions.
The data query language (DQL)
a high-level, English-like language that contains powerful, easy-to-use commands that enable users to retrieve, sort, order, and display data.
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RELATIONAL DATABASES
Types Of Attributes
A primary key
the database attribute, or combination of attributes, that uniquely identifies a specific row in a table.
A foreign key
An attribute in a table that is also a primary key in another table and is used to link the two tables.
Designing A Relational Database For S&S, INC
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