Chapter3 the relational data model and the relation database constraints part2

§  Constraints
§  Restrictions on the actual values in a database
state
§  Derived from the rules in the mini-world that the
database represents
§  Inherent model-based constraints or implicit
constraints
§  Inherent in the data model
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Relational model constraints
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Chapter
3:
The
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rela7onal
constraints

§  Inherent model-based constraints or implicit
constraints
§  Schema-based constraints or explicit
constraints
§  Can be directly expressed in schemas of the
data model
§  Application-based or semantic constraints or
business rules
§  Cannot be directly expressed in schemas
§  Expressed and enforced by application program
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Relational model constraints
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Chapter
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§  Typically include:
§  Numeric data types for integers and real
numbers
§  Characters
§  Booleans
§  Fixed-length strings
§  Variable-length strings
§  Date, time, timestamp
§  Money
§  Other special data types
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Domain constraints
Fundamentals
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Chapter
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§  Candidate key
§  Relation schema may have more than one key
§  Primary key of the relation
§  Designated among candidate keys
§  Underline attribute
§  Other candidate keys are designated as unique
keys
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Key constraints
Fundamentals
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Chapter
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The
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Key constraints
Fundamentals
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Chapter
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The
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constraints

§  Relational database schema S
§  Set of relation schemas S = {R1, R2, ..., Rm}
§  Set of integrity constraints IC
§  Relational database state
§  Set of relation states DB = {r1, r2, ..., rm}
§  Each ri is a state of Ri and such that the ri relation states
satisfy integrity constraints specified in IC
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Relational Databases and Relational Database schemas
Fundamentals
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Chapter
3:
The
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rela7onal
constraints

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Fundamentals
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Database

Chapter
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The
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rela7onal
constraints

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Fundamentals
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Chapter
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§  Invalid state
§  Does not obey all the integrity constraints
§  Valid state
§  Satisfies all the constraints in the defined set of
integrity constraints IC
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Fundamentals
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Chapter
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§  Entity integrity constraint
§  No primary key value can be NULL
§  Referential integrity constraint
§  Specified between two relations
§  Maintains consistency among tuples in two
relations
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Integrity, Referential Integrity, and foreign keys
Fundamentals
of
Database

Chapter
3:
The
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constraints

§  Foreign key rules:
§  The attributes in FK have the same domain(s)
as the primary key attributes PK
§  Value of FK in a tuple t1 of the current state
r1(R1) either occurs as a value of PK for some
tuple t2 in the current state r2(R2) or is NULL
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Fundamentals
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Chapter
3:
The
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model
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rela7onal
constraints

The conditions for a foreign key, given below, specify a
referential integrity constraint between the two relation
schemas R1 and R2. A set of attributes FK in relation schema
R1 is a foreign key of R1 that references relation R2 if it
satisfies the following rules:
1.  The attributes in FK have the same domain(s) as the
primary key attributes PK of R2; the attributes FK are said
to reference or refer to the relation R2.
2.  A value of FK in a tuple t1 of the current state r1(R1) either
occurs as a value of PK for some tuple t2 in the current
state r2(R2) or is NULL. In the former case, we have t1[FK]
= t2[PK], and we say that the tuple t1 references or refers
to the tuple t2.
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Fundamentals
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Chapter
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§  Diagrammatically display referential integrity constraints
§  Directed arc from each foreign key to the relation it
references
§  All integrity constraints should be specified on relational
database schema
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Fundamentals
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Chapter
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Fundamentals
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Chapter
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§  Semantic integrity constraints
§  May have to be specified and enforced on a
relational database
§  Use triggers and assertions
§  More common to check for these types of
constraints within the application programs
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Other types of constraints
Fundamentals
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Database

Chapter
3:
The
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rela7onal
constraints

§  Functional dependency constraint
§  Establishes a functional relationship among two
sets of attributes X and Y
§  Value of X determines a unique value of Y
§  State constraints
§  Define the constraints that a valid state of the
database must satisfy
§  Transition constraints
§  Define to deal with state changes in the database
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Other types of constraints
Fundamentals
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Chapter
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§  Operations of the relational model can be
categorized into retrievals and updates
§  Basic operations that change the states of
relations in the database:
§  Insert
§  Delete
§  Update (or Modify)
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Update operations, Transactions, and dealing with
constraint violations
Fundamentals
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Chapter
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§  Provides a list of attribute values for a new tuple t
that is to be inserted into a relation R
§  Can violate any of the four types of constraints
§  If an insertion violates one or more constraints
§  Default option is to reject the insertion
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The insertion operation
Fundamentals
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Chapter
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§  Can violate only referential integrity
§  If tuple being deleted is referenced by foreign keys from
other tuples
§  Restrict
•  Reject the deletion
§  Cascade
•  Propagate the deletion by deleting tuples that
reference the tuple that is being deleted
§  Set null or set default
•  Modify the referencing attribute values that cause the
violation
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The delete operation
Fundamentals
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Chapter
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§  Necessary to specify a condition on attributes of
relation
§  Select the tuple (or tuples) to be modified
§  If attribute not part of a primary key nor of a foreign
key
§  Usually causes no problems
§  Updating a primary/foreign key
§  Similar issues as with Insert/Delete
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The update operation
Fundamentals
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Chapter
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§  Transaction
§  Executing program
§  Includes some database operations
§  Must leave the database in a valid or consistent
state
§  Online transaction processing (OLTP) systems
§  Execute transactions at rates that reach several
hundred per second
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The transaction concept
Fundamentals
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Chapter
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The
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Chapter3 the relational data model and the relation database constraints part2

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Chapter3 the relational data model and the relation database constraints part2