CS145 Lecture Notes -- Object-Relational SQL
- Most major DBMS vendors now call their products "object-relational."
- There is great variation in OO functionality among current products.
- We'll cover a portion of the SQL-99 standard, as in the textbook.
- Oracle 9i has object support that does not adhere exactly to the
standard. (See our Oracle help document if interested.)
SQL-99 Object Support - Major Components
- Type definitions separate from table definitions
- Nested structures
- Methods
- References (pointers)
- Observer, generator, and mutator functions
- Ordering relationships
Type Definitions (UDT's)
- Separate from table definitions
- Can use for multiple tables
- Constraints on per-table basis
- Can use for attribute types (nested structures)
Original student table, recast:
CREATE TYPE StudentType
(ID integer, name char(30), address char(100), GPA float, SAT integer)
CREATE TABLE Student OF TYPE StudentType (PRIMARY KEY (ID))
Main difference (so far):
- Attribute references in queries must use ()
- Really invoking "observer methods"
Example: Find name, address of all students with GPA > 3.8 or SAT > 1450
Can use same type for multiple relations:
CREATE TABLE OldStudent OF TYPE StudentType PRIMARY KEY (name,address))
Note: Constraints are part of table declaration, not type declaration
Nested Structures
An attribute of a table can have a User-Defined Type (UDT)
Example: Use StudentType in student phone list:
CRATE TABLE Phone (student StudentType, number char(15))
But might better be done with references (see below)
Example: More structure in Student definition:
CREATE TYPE AddressType AS (street char(50), city char(50), zip integer)
CREATE TYPE ScoresType AS (GPA float, SAT integer)
CREATE TYPE StudentType AS
(ID integer, name char(30), address AddressType, scores ScoresType)
CREATE TABLE Student OF TYPE StudentType (PRIMARY KEY (ID))
(picture)
Note: no actual relations with types AddressType or ScoresType
Queries with Nesting
Just more dots
Example: Find name, street of all students from Palo Alto with GPA < 3.5
Methods
- Signature declared as part of type
- Method body implemented using, e.g., PL/SQL, PSM, or Java
Examples:
CREATE TYPE ScoresType AS (GPA float, SAT integer)
METHOD composite() RETURNS float
CREATE TYPE AddressType AS (street char(50), city char(50), zip integer)
METHOD sendto(name char(20), msg char(50)) RETURNS char(1)
Queries with Methods
Example: Return ID and composite score for all students
Example: Send "sorry" mailing to all students with composite score < 50.
Return ID and confirmation character as result of query.
References
- To be referenced, tuples must have an explicitly declared "reference
column"
- Reference column can be derived from primary key or purely
system-generated
Example: To make students referenceable:
CREATE TABLE Student OF TYPE StudentType
(PRIMARY KEY (ID),
REF IS SRef DERIVED) // alternative is SYSTEM GENERATED
Example: Student phone list:
CREATE TABLE Phone (student REF(StudentType), number char(15))
Phone tuples can reference any tuples of StudentType, e.g.,
in Student table and/or in OldStudent table (if it
contains "REF IS" clause).
Example: Student phone list without old students:
CREATE TABLE Phone
(student REF(StudentType) SCOPE Student, number char(15))
Queries with References
- Dereferencing operator DEREF
- Dereferencing and attribute selection operator "->"
Example: Phone numbers of students living in Mountain View
Example: Students with phone numbers containing "(408)"
Main effect of references is to eliminate joins.
Generator and Mutator Functions
For creating and updating values of UDT's
See book
Ordering Relationships
SQL uses equality and ordering of values in lots of places:
=, <, >, <=, >=, <>
ORDER BY
DISTINCT, GROUP BY
Would be nice to have these capabilities for UDT's also
Example: Students with phone numbers containing "(408)", ordered by
score
Statement:
CREATE ORDERING FOR <type> <ordering>
Details and defaults seem to be in flux. Basic idea:
If <ordering> specifies equals only:
- Two tuples are equal if and only if all components are equal
- If component is itself UDT, need ORDERING for that UDT
(and so on, recursively)
- Permits operations =, <>, DISTINCT, GROUP BY
If <ordering> specifies method-defined, all comparisons:
- Defined method takes two tuples and returns =, <, or >
- Permits operations =, <, > <=, >=, <>, ORDER BY, DISTINCT, GROUP BY
If <ordering> specifies method-defined, equals only:
- Defined method takes two tuples and returns = or <>
- Permits operations =, <>, DISTINCT, GROUP BY