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Relational database components:
DDL / Data Definition Language -
Defines the structure and schema of the database.
- Structure: table size, key placement, views and data element relationships.
- Schema: the type of data that will be held and manipulated and their properties.
DML / Data Manipulation Language -
All the commands that enable a user to view, manipulate and use the database.
QL / Query Language -
Enables users to make requests of the database.
Report Generator -
Produces printouts of data in a userdefined manner.
Data dictionary:
Is a central repository of data elements and their relationships.
Is a collection of data elements, schema objects and reference keys.
Schema objects - Can contain tables, views, indexes, procedures, functions and triggers.
Keys:
Primary key -
Is a unique identifier in the table that unambiguously point to an individual tuple or row in the table.
Is a subset of candidate keys within a table.
Foreing key -
An attribute (column) in one relation that has values matching the primary key in another relation.
Integrity:
Concurrency problems -
Making sure that different subjects receive the most up-to-date information.
Semantic integrity -
Makes sure that structural and semantic rules are enforced. These rules pertain to data types, logical values, uniqueness constraints and operations that could adversely affect the structure of the database.
Referential integrity -
Mechanism would ensure that no record would contain a reference to a primary key of a nonexisting record or a NULL value.
Entity integrity -
If an attribute is NULL.
Rollback -
Is a statement that ends a current transaction and cancels all other changes to the database.
Commit -
Terminates a transaction and executes all changes that were just made by the user.
Checkpoint -
Are used to make sure that if a system failure occurs or if an error is detected, the user can always return to a point in time before the system crashed.
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