Advanced Database
CS-426
Week 2 – Logic Query Languages,
Object Model
Object Models
An object typically has two components: state (value) and behavior (operations). One goal of an ODMS
(Object Data Management System) is to maintain a direct correspondence between real-world and
database objects so that objects do not lose their integrity and identity and can easily be identified and
operated upon.
define type EMPLOYEE
tuple ( Fname: string;
Minit: char;
Lname: string;
Ssn: string;
Birth_date: DATE;
Address: string;
Sex: char;
Salary: float;
Supervisor: EMPLOYEE;
Dept: DEPARTMENT;);
Object Models
define type DATE
tuple ( Year: integer;
Month: integer;
Day: integer; );
Object Data Modeling Group
(ODMG)
• The ODMG object model is the data model upon which the
object definition language (ODL) and object query language
(OQL) are based. It is meant to provide a standard data model
for object databases, just as SQL describes a standard data
model for relational databases. It also provides a standard
terminology in a field where the same terms were sometimes
used to describe different concepts.
Object Definition Language (ODL)
• The ODL is designed to support the semantic constructs of the
ODMG object model and is independent of any particular
programming language. Its main use is to create object
specifications—that is, classes and interfaces. Hence, ODL is not
a full programming language. A user can specify a database
schema in ODL independently of any programming language,
and then use the specific language bindings to specify how ODL
constructs can be mapped to constructs in specific
programming languages, such as C++, Smalltalk, and Java.
Object Query Language (OQL)
• The object query language OQL is the query language
proposed for the ODMG object model. It is designed to work
closely with the programming languages for which an ODMG
binding is defined, such as C++, Smalltalk, and Java. Hence, an
OQL query embedded into one of these programming
languages can return objects that match the type system of that
language. Additionally, the implementations of class operations
in an ODMG schema can have their code written in these
programming languages. The OQL syntax for queries is similar to
the syntax of the relational standard query language SQL, with
additional features for ODMG concepts, such as object identity,
complex objects, operations, inheritance, polymorphism, and
relationships.
Advanced SQL
1. Accessing SQL From a Programming Language
There are two approaches to accessing SQL from a general-purpose
programming language:
• Dynamic SQL: A general-purpose program can connect to and
communicate with a database server using a collection of functions (for
procedural languages)or methods (for object-oriented languages).
Dynamic SQL allows the program to construct an SQL query as a
character string at runtime, submit the query, and then retrieve the result
into program variables a tuple at a time. The dynamic SQL component
of SQL allows programs to construct and submit SQL queries at runtime.
Advanced SQL
• Embedded SQL: Like dynamic SQL, embedded SQL provides a
means by which a program can interact with a database server.
However, under embedded SQL, the SQL statements are
identified at compile time using a preprocessor. The
preprocessor submits the SQL statements to the database system
for precompilation and optimization; then it replaces the SQL
statements in the application program with appropriate code
and function calls before invoking the programming-language
compiler.
2. Functions and Procedures
Procedures and functions allow “business logic” to be stored in the
database, and executed from SQL statements.
Example:
create function dept count(dept name varchar(20))
returns integer
begin
declare d count integer;
select count(*) into d count
from instructor
where instructor.dept name= dept name
return d count;
end
3. Triggers
A trigger is a statement that the system executes automatically as
a side effect of a modification to the database. To design a trigger
mechanism, we must meet two requirements:
1. Specify when a trigger is to be executed. This is broken up into
an event that causes the trigger to be checked and a condition
that must be satisfied for trigger execution to proceed.
2. Specify the actions to be taken when the trigger executes.