The Database Environment Chapter 15

1
© Prentice Hall, 2002
Chapter 15:Chapter 15:
Object-Oriented DatabaseObject-Oriented Database
DevelopmentDevelopment
Modern Database Management
6th
Edition
Jeffrey A. Hoffer, Mary B. Prescott, Fred R.
McFadden

2Chapter 15 © Prentice Hall,
Object Definition LanguageObject Definition Language
(ODL)(ODL)
Corresponds to SQL’s DDL (Data
Definition Language)
Specify the logical schema for an object-
oriented database
Based on the specifications of Object
Database Management Group (ODMG)

Defining a ClassDefining a Class
classclass – keyword for defining classes
attributeattribute – keyword for attributes
operationsoperations – return type, name, parameters
in parentheses
relationshiprelationship – keyword for establishing
relationship

Defining an AttributeDefining an Attribute
 Value can be either:
– Object identifier OR Literal
 Types of literals
– Atomic – a constant that cannot be decomposed into components
– Collection – multiple literals or object types
– Structure – a fixed number of named elements, each of which could be a
literal or object type
 Attribute ranges
– Allowable values for an attribute
– enum – for enumerating the allowable values

Kinds of CollectionsKinds of Collections
 Set – unordered collection without duplicates
 Bag – unordered collection that may contain
duplicates
 List – ordered collection, all the same type
 Array – dynamically sized ordered collection,
locatable by position
 Dictionary – unordered sequence of key-value
pairs without duplicates

Defining StructuresDefining Structures
Structure = user-defined type with components
structstruct keyword
Example:
struct Address {struct Address {
String street_addressString street_address
String city;String city;
String state;String state;
String zip;String zip;
};};

Defining OperationsDefining Operations
Return type
Name
Parentheses following the name
Arguments within the
parentheses

Defining RelationshipsDefining Relationships
 Only unary and binary relationships allowed
 Relationships are bi-directional
– implemented through use of inverse keyword
 ODL relationships are specified:
– relationship indicates that class is on many-side
– relationship set indicates that class is on one-side and
other class (many) instances unordered
– relationship list indicates that class is on one-side and
other class (many) instances ordered

Figure 15-1 –UML class diagram for a university database
The following slides illustrate the
ODL implementation of this
UML diagram

Figure 15-2 –ODL Schema for university database

class keyword begins
the class
definition.Class
components enclosed
between { and }

Figure 15-2 – ODL Schema for university database
attribute has a data type and a name
specify allowable values
using enum

extent = the set of all instances of the class

Operation definition:
return type, name, and
argument list.
Arguments include
data types and names

relationship sets indicate 1:N relationship to an
unordered collection of instances of the other class
inverse establishes the bidirectionality of the relationship

relationship list indicates 1:N relationship to an
ordered collection of instances of the other class

relationship indicates N:1 relationship to an
instance of the other class

Figure 15-3 – UML class diagram for an employee project database
(a) Many-to-many relationship with an association class
Note:
In order to
capture special
features of
assignment, this
should be
converted into
two 1:N
relationships

Figure 15-3 – UML class diagram for an employee project database
(b) Many-to many relationship broken into two one-to-many relationships
class Employee {
(extent employees
key emp_id)
………….
attribute set (string) skills_required;
};
Note:
key indicates indentifier
(candidate key)
Note: attribute set indicates a
multivalued attribute

Figure 15-4
UML class diagram showing employee generalization
class Employee
extends Employee{
( ………….
………….
} Note:
extends
denotes
subclassing

Figure 15-5 –UML class diagram showing student generalization
abstract class Student
extends Employee{
( ………….
abstract float calc_tuition();
}
Note: abstract operation denotes no
method (no implementation) of
calc_tuition at the Student level
Note: abstract class denotes non-
instantiable (complete constraint)

Creating Object InstancesCreating Object Instances
 Specify a tag that will be the object identifier
– MBA699 course ();
 Initializing attributes:
– Cheryl student (name: “Cheryl Davis”, dateOfBirth:4/5/77);
 Initializing multivalued attributes:
– Dan employee (emp_id: 3678, name: “Dan Bellon”,
skills {“Database design”, “OO
Modeling”});
 Establishing links for relationship
– Cheryl student (takes: {OOAD99F, Telecom99F, Java99F});

Querying Objects in the OODBQuerying Objects in the OODB
 Object Query Language (OQL)
 ODMG standard language
 Similar to SQL-92
 Some differences:
– Joins use class’s relationship name:
 Select x.enrollment from courseofferings x, x.belongs_to y
where y.crse_course = “MBA 664” and x.section = 1;
– Using a set in a query
 Select emp_id, name from employees where “Database
Design” in skills;

Current ODBMS ProductsCurrent ODBMS Products
 Rising popularity due to:
– CAD/CAM applications
– Geographic information systems
– Multimedia
– Web-based applications
– Increasingly complex data types
 Applications of ODBMS
– Bill-of-material
– Telecommunications navigation
– Health care
– Engineering design
– Finance and trading

Table15-1 – ODBMS Products

The Database Environment Chapter 15

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The Database Environment Chapter 15