OBJECT-ORIENTED DATABASE (OODB)

What is Object database

An object database (also object-oriented database management system) is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which are table-oriented. Object-relational databases are a hybrid of both approaches.

WHY OBJECT-ORIENTED DATABASE?

• Industry Trends: Integration and Sharing
• Seamless integration of operating systems, databases, languages, spreadsheets, word processors, AI expert system shells.
• Sharing of data, information, software components, products, computing environments.
• Referential sharing: Multiple applications, products, or objects share common sub-objects. (Hypermedia links are then used to navigate from one object to another)
• Object-oriented databases allows referential sharing through the support of object identity and inheritance.

Fundamentals of Object-Oriented Approach

The object-oriented paradigm is illustrated below:

Objects and Identity

The following figure shows object with state and behavior. The state is represented by the values of the object's attributes, and the behavior is defined by the methods acting on the state of the object. There is a unique object identifier OID to identify the object.

Complex Objects

Complex objects are built by applying constructors to simpler objects including: sets, lists and tuples. An example is illustrated below:

Encapsulation

Encapsulation is derived from the notion of Abstract Data Type (ADT). It is motivated by the need to make a clear distinction between the specification and the implementation of an operation. It reinforces modularity and provides a form of logical data independence.

Class

A class object is an object which acts as a template. It specifies:

• A structure that is the set of attributes of the instances
• A set of operations
• A set of methods which implement the operations

Instantiation means generating objects, Ex. 'new' operation in C++

• Persistence of objects: Two approaches
• An implicit characteristic of all objects
• An orthogonal characteristic - insert the object into a persistent collection of objects

Inheritance

A mechanism of reusability, the most powerful concept of OO programming

Association

• Association is a link between entities in an application
• In OODB, associations are represented by means of references between objects
• a representation of a binary association
• a representation of a ternary association
• reverse reference

ADVANTAGES OF OODB

• An integrated repository of information that is shared by multiple users, multiple products, multiple applications on multiple platforms.

It also solves the following problems:

• The semantic gap: The real world and the Conceptual model is very similar.
• Impedance mismatch: Programming languages and database systems must be interfaced to solve application problems. But the language style, data structures, of a programming language (such as C) and the DBMS (such as Oracle) are different. The OODB supports general purpose programming in the OODB framework.
• New application requirements: Especially in OA, CAD, CAM, CASE, object-orientation is the most natural and most convenient.

COMPLEX OBJECT DATA MODELS

Complex object data model is non-1NF data model. It allows the following extensions:
1. Sets of atomic values
2. Tuple-valued attributes
3. Sets of tuples (nested relations)
4. General set and tuple constructors
5. Object identity
Formal definition:
1. Every atomic value in A is an object.
2. If a1, ..., an are attribute names in N, and O1, ..., On are objects, then T = [a1:O1, ..., an:On] is also an object, and T.ai retrieves the value Oi.
3. If O1, ..., On are objects, then S = {O1, ..., On} is an abject.

Semantic Data Models

The following figure shows different types of nodes in GSM.

The different types of links (relationships) in GSM are shown below.

A semantic model for the sales office automation example is shown below.

An entity-relationship model for the sales office automation example is shown below.

OBJECT-ORIENTED DATABASES

OODB = Object Orientation + Database Capabilities
FEATURES TO BE CONSIDERED:
persistence
support of transactions
simple querying of bulk data
concurrency control
resilience and recovery
security
versioning
integrity
performance issues

DATA MODELS TO BE CONSIDERED:

Complex object model
Semantic data model such as Extended ER (EER) model, OPM model
NOT ALL OODB SUPPORTS SAME OBJECT-ORIENTATION, SAME DATA MODEL AND SAME SET OF FEATURES

RESEARCH PROTOTYPES

• ORION: Lisp-based system, built at MCC 1987. Handles schema evolution and complex object locking.
• IRIS: Built at HP 1987. Functional data model, version control, object-SQL.
• Galileo: Built at Univ Pisa 1985. Strong typed language, complex objects.
• PROBE: CCA 1986.
• POSTGRES: Univ. California, Berkeley 1990. Extended relational database supporting objects.

COMMERCIAL OODB

• O2: O2 Technology. Language O2C to define classes, methods and types. Supports multiple inheritance. C++ compatible. Supports an extended SQL language O2SQL which can refer to complex objects.
• G-Base: Graphael 1987. Lisp-based system, supports ADT, multiple inheritance of classes.
• CORBA: Standards for distributed objects.
• GemStone: Servio Logic 1987, Beaverton, Oregon. Earliest OODB supporting object identity, inheritance, encapsulation. Language OPAL is based upon Smalltalk.
• Ontos: Ontologic, 1988, Berlington, Mass. C++ based system, offers C++ clients library. Ontos has a predecessor called Vbase.
• Ontos model supports encapsulation, inheritance, ability to construct complex objects.
• Object Store: Object Design Inc. C++ based sustem. A good feature is that it supports the creation of indexes.
• Statics: Symbolics 1988. Supports entity types, set valued attributes, and inheritance of entity types and methods.

COMMERCIAL OODB (continued)

• SIM: Semantic Information Manager, UNISYS 1987. Supports semantic data model. Core system of the InfoExec Environment of UNISYS. Uses the Semantic Data Model of Hammer and McLeod 1981. User can define entity types that can inherit from one another.Attributes of entities are like functions from one entity to another.
• Relational DB Extensions: Many relational systems support OODB extensions.

1. User-defined functions (dBase).
2. User-defined ADTs (POSTGRES)
3. Very-long multimedia fields (BLOB or Binary Large Object). (DB2 from IBM, SQL from SYBASE, Informix, Interbase)

ALTERNATIVE OODB STRATEGIES

1. Develop novel database data model or data language (SIM)
2. Extend an existing database language with object-oriented capabilities. (IRIS, O2 and VBASE/ONTOS extended SQL)
3. Extend existing object-oriented programming language with database capabilities (GemStone OPAL extended SmallTalk)
4. Extendable object-oriented DBMS library (ONTOS)

OODB QUERY LANGUAGE

ONTOS (from Ontologic), O2 (from O2 Technology) and IRIS (from HP) all offer object-oriented extension of SQL.
IRIS has Object SQL. Each entity type specifies one or more properties. Properties are functions that apply to the instances of the type. Entity types have extensions and can inherit from one another.
Example: The type PERSON can be created by:
Create Type Person (
Name char(20),
Age integer
Address address)
where address is another type. In IRIS, Name, Age and Address are called properties (functions) and apply to instances of type Person.

OODB QUERY LANGUAGE

ONTOS (from Ontologic), O2 (from O2 Technology) and IRIS (from HP) all offer object-oriented extension of SQL.
IRIS has Object SQL. Each entity type specifies one or more properties. Properties are functions that apply to the instances of the type. Entity types have extensions and can inherit from one another.
Example: The type PERSON can be created by:
Create Type Person (
Name char(20),
Age integer
Address address)
where address is another type. In IRIS, Name, Age and Address are called properties (functions) and apply to instances of type Person.

OODB QUERY LANGUAGE (continued)

Object SQL Query: retrieve the name and state of all people who are older than 21:
Select Name(p), State(Address(p)
for each Person p
where Age(p) > 21
(Here we assume address has another property called "state")
The user can compose the function application:
P5(P4(...P1(P))...)
in the select statement.
EXAMPLE:
Employee is a subtype of Person
SalesPerson is a subtype of Employee
Addresses have street names
Salespeople have sales managers
sales managers have secretaries
secretaries are employees
Retrieve the street name of the address of the secretary of the manager of each salesperson whose salary is more than 50,000:
Select
StreetName(Address(Secretary(Manager(0))))
for each SalesPerson p
where Salary(p) > $50,000

WHY EXTENDING SQL?

• SQL is the most popular relational query language
• SQL is also the only relational language that has a standard.
• SQL is being promoted by many companies as the interface language for database engines and database servers. New applications developed in SQL extensions can easily call these servers for remote access.d