DBMSSpring 2014

Database Integrity

Sources:Security in Computing, Pfleeger and Pfleeger, Prentice Hall, 2003

Lecture Slides, CSE6243, MSU, Rayford B. Vaughn, 2005http://www.postgresql.org/docs/9.0/static/ddl-constraints.html

First, a followup from Tues

R(A, B, C, D, E) with FDs AB -> C C -> D A -> E

What violations of 3nf are found? How would you decompose this?

Followup from Tues

R(A, B, C, D) with FDs AB -> C C -> D D -> A

What are the possible keys to this relation? What violations of 3nf are found? How would you decompose this?

Book, page 92, 3.3.5.1

Traditional Security Concerns

Confidentiality Integrity Availability Accountability

Traditional Security Concerns

Confidentiality

Integrity Availability Accountability

Integrity

DB integrity types Physical Database Integrity

– Data in Database is safe– Data can be reconstructed

Logical Database Integrity– Structure of Database is preserved– No inconsistency

Element Integrity – Correctness/accuracy of data is maintained

Integrity Goals

Database integrity protection must achieve: Internal consistency: database entries must obey prescribed

rules; External consistency: database entries are correct - combine

checking data entered with auditing to check consistent state.

Integrity Rules

Most rules are application specific, but two rules inherent to relational database model: Entity integrity rule:

– no component of primary key can accept nulls. Referential integrity rule:

– database must not contain unmatched foreign key values.

Application Specific Integrity Checks

field checks: check that entries are valid elements of domain consistency checks: check that entries in different relations do not

conflict scope checks: checks that query results are not computed for too

small a sample (for specialized DB) change logs: check that all changes are recorded with original and

modified entry values

Integrity in postresql

Primary keys Must be unique Must be non-null

Foreign keys - http://www.postgresql.org/docs/8.1/static/tutorial-fk.html Field can be null or not-null If null, we can have a row without the foreign key

attribute present, but if the attribute is filled in, it must match a row in the referenced table.

Thinking about foreign keys

If a Foreign Key references another table and the other table row is deleted, what should happen to the referencing row.

For example, dlangs references languages. What if we decide that a language really isn’t a language and so we remove it. ie. PigLatin. What should happen? No Action / Restrict On Delete Cascade On Update Cascade (what happens if we change)

Other constraints

“Table constraints” Field contraints

Can be built into the CREATE TABLE OR Can be added using the ALTER TABLE

Other constraints

Null is assumed for a non-key attribute added to a table.

NOT NULL requires a value to be filled in. SSN int NOT NULL,

UNIQUE requires that no other row can have the same value. SSN int UNIQUE NOT NULL,

Field vs Table levelfrom Postgresql reference

CREATE TABLE products ( product_no integer UNIQUE, name text, price numeric );

CREATE TABLE products ( product_no integer, name text, price numeric, UNIQUE (product_no) );

CREATE TABLE example ( a integer, b integer, c integer, UNIQUE (a, c) );

Check Constraints

Allow us to more finely define field values beyond the overall domain (data type)

For example, can a driver have a vehicle with -5 seats? Can a driver have a vehicle with 192 seats? What is the restriction to insure that we have a reasonable number.

CREATE TABLE products ( product_no integer, name text, price numeric CHECK (price > 0) );

Named constraintsCREATE TABLE products ( product_no integer, name text, price numeric CONSTRAINT positive_price CHECK (price > 0) );

Table levelCREATE TABLE products ( product_no integer, name text, price numeric CHECK (price > 0), discounted_price numeric CHECK (discounted_price > 0),

CHECK (price > discounted_price) );

Adding constraints

ALTER TABLE

Can add table level constraints.

Default values

CREATE TABLE distributors ( name varchar(40) DEFAULT 'Luso Films', did integer DEFAULT nextval('distributors_serial'), modtime timestamp DEFAULT current_timestamp );